Internet DRAFT - draft-irtf-pearg-numeric-ids-history
draft-irtf-pearg-numeric-ids-history
Internet Research Task Force (IRTF) F. Gont
Internet-Draft SI6 Networks
Intended status: Informational I. Arce
Expires: 14 June 2023 Quarkslab
11 December 2022
Unfortunate History of Transient Numeric Identifiers
draft-irtf-pearg-numeric-ids-history-11
Abstract
This document analyzes the timeline of the specification and
implementation of different types of "transient numeric identifiers"
used in IETF protocols, and how the security and privacy properties
of such protocols have been affected as a result of it. It provides
empirical evidence that advice in this area is warranted. This
document is a product of the Privacy Enhancement and Assessment
Research Group (PEARG) in the IRTF.
Status of This Memo
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This Internet-Draft will expire on 14 June 2023.
Copyright Notice
Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Threat Model . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Issues with the Specification of Transient Numeric
Identifiers . . . . . . . . . . . . . . . . . . . . . . . 5
4.1. IPv4/IPv6 Identification . . . . . . . . . . . . . . . . 6
4.2. TCP Initial Sequence Numbers (ISNs) . . . . . . . . . . . 10
4.3. IPv6 Interface Identifiers (IIDs) . . . . . . . . . . . . 12
4.4. NTP Reference IDs (REFIDs) . . . . . . . . . . . . . . . 15
4.5. Transport Protocol Ephemeral Port Numbers . . . . . . . . 16
4.6. DNS Query ID . . . . . . . . . . . . . . . . . . . . . . 17
5. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 19
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
7. Security Considerations . . . . . . . . . . . . . . . . . . . 19
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 20
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 20
9.1. Normative References . . . . . . . . . . . . . . . . . . 20
9.2. Informative References . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 34
1. Introduction
Networking protocols employ a variety of transient numeric
identifiers for different protocol objects, such as IPv4 and IPv6
Fragment Identifiers [RFC0791] [RFC8200], IPv6 Interface Identifiers
(IIDs) [RFC4291], transport protocol ephemeral port numbers
[RFC6056], TCP Initial Sequence Numbers (ISNs) [RFC0793], NTP
Reference IDs (REFIDs) [RFC5905], and DNS Query IDs [RFC1035]. These
identifiers typically have specific interoperability requirements
(e.g. uniqueness during a specified period of time), and associated
failure severities when such requirements are not met
[I-D.irtf-pearg-numeric-ids-generation].
For more than 30 years, a large number of implementations of the IETF
protocols have been subject to a variety of attacks, with effects
ranging from Denial of Service (DoS) or data injection, to
information leakages that could be exploited for pervasive monitoring
[RFC7258]. The root cause of these issues has been, in many cases,
poor selection of transient numeric identifiers, usually as a result
of insufficient or misleading specifications.
For example, implementations have been subject to security or privacy
issues resulting from:
* Predictable IPv4 or IPv6 Fragment Identifiers (see e.g.
[Sanfilippo1998a], [RFC6274], and [RFC7739])
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* Predictable IPv6 IIDs (see e.g. [RFC7721], [RFC7707], and
[RFC7217])
* Predictable transport protocol ephemeral port numbers (see e.g.
[RFC6056] and [Silbersack2005])
* Predictable TCP Initial Sequence Numbers (ISNs) (see e.g.
[Morris1985], [Bellovin1989], and [RFC6528])
* Predictable DNS Query IDs (see e.g. [Arce1997] and [Klein2007])
These examples indicate that when new protocols are standardized or
implemented, the security and privacy properties of the associated
transient numeric identifiers tend to be overlooked, and
inappropriate algorithms to generate such identifiers (i.e. that
negatively affect the security or privacy properties of the protocol)
are either suggested in the specification or selected by
implementers.
This document contains a non-exhaustive timeline of the specification
and vulnerability disclosures related to some sample transient
numeric identifiers, including other work that has led to advances in
this area. This analysis indicates that:
* Vulnerabilities associated with the inappropriate generation of
transient numeric identifiers have affected protocol
implementations for an extremely long period of time.
* Such vulnerabilities, even when addressed for a given protocol
version, were later reintroduced in new versions or new
implementations of the same protocol.
* Standardization efforts that discuss and provide advice in this
area can have a positive effect on IETF specifications and their
corresponding implementations.
While it is generally possible to identify an algorithm that can
satisfy the interoperability requirements for a given transient
numeric identifier, this document provides empirical evidence that
doing so without negatively affecting the security or privacy
properties of the aforementioned protocols is non-trivial. Other
related documents ([I-D.irtf-pearg-numeric-ids-generation] and
[I-D.gont-numeric-ids-sec-considerations]) provide guidance in this
area, as motivated by the present document.
This document represents the consensus of the Privacy Enhancement and
Assessment Research Group (PEARG).
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2. Terminology
Transient Numeric Identifier:
A data object in a protocol specification that can be used to
definitely distinguish a protocol object (a datagram, network
interface, transport protocol endpoint, session, etc) from all
other objects of the same type, in a given context. Transient
numeric identifiers are usually defined as a series of bits, and
represented using integer values. These identifiers are typically
dynamically selected, as opposed to statically-assigned numeric
identifiers (see e.g. [IANA-PROT]). We note that different
identifiers may have additional requirements or properties
depending on their specific use in a protocol. We use the term
"transient numeric identifier" (or simply "numeric identifier" or
"identifier" as short forms) as a generic term to refer to any
data object in a protocol specification that satisfies the
identification property stated above.
The terms "constant IID", "stable IID", and "temporary IID" are to be
interpreted as defined in [RFC7721].
3. Threat Model
Throughout this document, we do not consider on-path attacks. That
is, we assume the attacker does not have physical or logical access
to the system(s) being attacked, and that the attacker can only
observe traffic explicitly directed to the attacker. Similarly, an
attacker cannot observe traffic transferred between a sender and the
receiver(s) of a target protocol, but may be able to interact with
any of these entities, including by e.g. sending any traffic to them
to sample transient numeric identifiers employed by the target
systems when communicating with the attacker.
For example, when analyzing vulnerabilities associated with TCP
Initial Sequence Numbers (ISNs), we consider the attacker is unable
to capture network traffic corresponding to a TCP connection between
two other hosts. However, we consider the attacker is able to
communicate with any of these hosts (e.g., establish a TCP connection
with any of them), to e.g. sample the TCP ISNs employed by these
systems when communicating with the attacker.
Similarly, when considering host-tracking attacks based on IPv6
interface identifiers, we consider an attacker may learn the IPv6
address employed by a victim node if e.g. the address becomes exposed
as a result of the victim node communicating with an attacker-
operated server. Subsequently, an attacker may perform host-tracking
by probing a set of target addresses composed by a set of target
prefixes and the IPv6 interface identifier originally learned by the
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attacker. Alternatively, an attacker may perform host tracking if
e.g. the victim node communicates with an attacker-operated server as
it moves from one location to another, those exposing its configured
addresses. We note that none of these scenarios requires the
attacker observe traffic not explicitly directed to the attacker.
4. Issues with the Specification of Transient Numeric Identifiers
While assessing IETF protocol specifications regarding the use of
transient numeric identifiers, we have found that most of the issues
discussed in this document arise as a result of one of the following
conditions:
* Protocol specifications that under-specify the requirements for
their transient numeric identifiers
* Protocol specifications that over-specify their transient numeric
identifiers
* Protocol implementations that simply fail to comply with the
specified requirements
A number of IETF protocol specifications have simply overlooked the
security and privacy implications of transient numeric identifiers.
Examples of them are the specification of TCP ephemeral ports in
[RFC0793], the specification of TCP sequence numbers in [RFC0793], or
the specification of the DNS TxID in [RFC1035].
On the other hand, there are a number of IETF protocol specifications
that over-specify some of their associated transient numeric
identifiers. For example, [RFC4291] essentially overloads the
semantics of IPv6 Interface Identifiers (IIDs) by embedding link-
layer addresses in the IPv6 IIDs, when the interoperability
requirement of uniqueness could be achieved in other ways that do not
result in negative security and privacy implications [RFC7721].
Similarly, [RFC2460] suggested the use of a global counter for the
generation of Fragment Identification values, when the
interoperability properties of uniqueness per {Src IP, Dst IP} could
be achieved with other algorithms that do not result in negative
security and privacy implications [RFC7739].
Finally, there are implementations that simply fail to comply with
the corresponding IETF protocol specifications or recommendations.
For example, some popular operating systems (notably Microsoft
Windows) still fail to implement transport protocol ephemeral port
randomization, as recommended in [RFC6056].
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The following subsections document the timelines for a number of
sample transient numeric identifiers, that illustrate how the problem
discussed in this document has affected protocols from different
layers over time. These sample transient numeric identifiers have
different interoperability requirements and failure severities (see
Section 6 of [I-D.irtf-pearg-numeric-ids-generation]), and thus are
considered to be representative of the problem being analyzed in this
document.
4.1. IPv4/IPv6 Identification
This section presents the timeline of the Identification field
employed by IPv4 (in the base header) and IPv6 (in Fragment Headers).
The reason for presenting both cases in the same section is to make
it evident that while the Identification value serves the same
purpose in both IPv4 and IPv6, the work and research done for the
IPv4 case did not affect IPv6 specifications or implementations.
The IPv4 Identification is specified in [RFC0791], which specifies
the interoperability requirements for the Identification field: the
sender must choose the Identification field to be unique for a given
source address, destination address, and protocol, for the time the
datagram (or any fragment of it) could be alive in the internet. It
suggests that a node may keep "a table of Identifiers, one entry for
each destination it has communicated with in the last maximum packet
lifetime for the internet", and suggests that "since the Identifier
field allows 65,536 different values, hosts may be able to simply use
unique identifiers independent of destination". The above has been
interpreted numerous times as a suggestion to employ per-destination
or global counters for the generation of Identification values.
While [RFC0791] does not suggest any flawed algorithm for the
generation of Identification values, the specification omits a
discussion of the security and privacy implications of predictable
Identification values. This has resulted in many IPv4
implementations generating predictable fragment Identification values
by means of a global counter, at least at some point in time.
The IPv6 Identification was originally specified in [RFC1883]. It
serves the same purpose as its IPv4 counterpart, with the only
difference residing in the length of the corresponding field, and
that while the IPv4 Identification field is part of the base IPv4
header, in the IPv6 case it is part of the Fragment header (which may
or may not be present in an IPv6 packet). [RFC1883] states, in
Section 4.5, that the Identification must be different than that of
any other fragmented packet sent recently (within the maximum likely
lifetime of a packet) with the same Source Address and Destination
Address. Subsequently, it notes that this requirement can be met by
means of a wrap-around 32-bit counter that is incremented each time a
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packet must be fragmented, and that it is an implementation choice
whether to use a global or a per-destination counter. Thus, the
implementation of the IPv6 Identification is similar to that of the
IPv4 case, with the only difference that in the IPv6 case the
suggestions to use simple counters is more explicit. [RFC2460] was
the first revision of the core IPv6 specification, and maintained the
same text for the specification of the IPv6 Identification field.
[RFC8200], the second revision of the core IPv6 specification,
removes the suggestion from [RFC2460] to use a counter for the
generation of IPv6 Identification values, and points to [RFC7739] for
sample algorithms for their generation.
September 1981:
[RFC0791] specifies the interoperability requirements for IPv4
Identification value, but does not perform a vulnerability
assessment of this transient numeric identifier.
December 1995:
[RFC1883], the first specification of the IPv6 protocol, is
published. It suggests that a counter be used to generate the
IPv6 Identification value, and notes that it is an implementation
choice whether to maintain a single counter for the node or
multiple counters, e.g., one for each of the node's possible
source addresses, or one for each active (source address,
destination address) combination.
December 1998:
[Sanfilippo1998a] finds that predictable IPv4 Identification
values (generated by most popular implementations) can be
leveraged to count the number of packets sent by a target node.
[Sanfilippo1998b] explains how to leverage the same vulnerability
to implement a port-scanning technique known as "dumb/idle scan".
A tool that implements this attack is publicly released.
December 1998:
[RFC2460], a revision of the IPv6 specification, is published,
obsoleting [RFC1883]. It maintains the same specification of the
IPv6 Identification field as its predecessor ([RFC1883]).
December 1998:
OpenBSD implements randomization of the IPv4 Identification field
[OpenBSD-IPv4-ID].
November 1999:
[Sanfilippo1999] discusses how to leverage predictable IPv4
Identification to uncover the rules of a number of firewalls.
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September 2002:
[Fyodor2002] documents the implementation of the "idle/dumb scan"
technique in the popular nmap tool.
November 2002:
[Bellovin2002] explains how the IPv4 Identification field can be
exploited to count the number of systems behind a NAT.
October 2003:
OpenBSD implements randomization of the IPv6 Identification field
[OpenBSD-IPv6-ID].
December 2003:
[Zalewski2003] explains a technique to perform TCP data injection
attacks based on predictable IPv4 identification values, which
requires less effort than TCP injection attacks performed with
bare TCP packets.
November 2005:
[Silbersack2005] discusses shortcomings in a number of techniques
to mitigate predictable IPv4 Identification values.
October 2007:
[Klein2007] describes a weakness in the pseudo random number
generator (PRNG) in use for the generation of the IP
Identification by a number of operating systems.
June 2011:
[Gont2011] describes how to perform dumb/idle scan attacks in
IPv6.
November 2011:
Linux mitigates predictable IPv6 Identification values
[RedHat2011] [SUSE2011] [Ubuntu2011].
December 2011:
[draft-gont-6man-predictable-fragment-id-00] describes the
security implications of predictable IPv6 Identification values,
and possible mitigations. This document has the Intended Status
of "Standards Track", with the intention to formally update
[RFC2460], to introduce security and privacy requirements on the
generation of IPv6 Identification values.
May 2012:
[Gont2012] notes that some major IPv6 implementations still employ
predictable IPv6 Identification values.
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March 2013:
The 6man WG adopts [I-D.gont-6man-predictable-fragment-id], but
changes the track to "BCP" (while still formally updating
[RFC2460]), publishing the resulting document as
[draft-ietf-6man-predictable-fragment-id-00].
June 2013:
A patch to incorporate support for IPv6-based idle/dumb scans in
nmap is submitted [Morbitzer2013].
December 2014:
The 6man WG changes the Intended Status of
[draft-ietf-6man-predictable-fragment-id-01] to "Informational"
and publishes it as [draft-ietf-6man-predictable-fragment-id-02].
As a result, it no longer formally updates [RFC2460], and security
and privacy requirements on the generation of IPv6 Identification
values are eliminated.
June 2015:
[draft-ietf-6man-predictable-fragment-id-08] notes that some
popular host and router implementations still employ predictable
IPv6 Identification values.
February 2016:
[RFC7739] (based on [I-D.ietf-6man-predictable-fragment-id])
analyzes the security and privacy implications of predictable IPv6
Identification values, and provides guidance for selecting an
algorithm to generate such values. However, being published with
the Intended Status of "Informational", it does not formally
update [RFC2460], and does not introduce security and privacy
requirements on the generation of IPv6 Identification values.
June 2016:
[I-D.ietf-6man-rfc2460bis], revision of [RFC2460], removes the
suggestion from RFC2460 to use a counter for the generation of
IPv6 Identification values, but does not perform a vulnerability
assessment of the generation of IPv6 Identification values, and
does not introduce security and privacy requirements on the
generation of IPv6 Identification values.
July 2017:
[I-D.ietf-6man-rfc2460bis] is finally published as [RFC8200],
obsoleting [RFC2460], and pointing to [RFC7739] for sample
algorithms for the generation of IPv6 Fragment Identification
values. However, it does not introduce security and privacy
requirements on the generation of IPv6 Identification values.
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June 2019:
[IPID-DEV] notes that the IPv6 ID generators of two popular
operating systems are flawed.
4.2. TCP Initial Sequence Numbers (ISNs)
[RFC0793] suggests that the choice of the ISN of a connection is not
arbitrary, but aims to reduce the chances of a stale segment from
being accepted by a new incarnation of a previous connection.
[RFC0793] suggests the use of a global 32-bit ISN generator that is
incremented by 1 roughly every 4 microseconds. However, as a matter
of fact, protection against stale segments from a previous
incarnation of the connection is enforced by preventing the creation
of a new incarnation of a previous connection before 2*MSL have
passed since a segment corresponding to the old incarnation was last
seen (where "MSL" is the "Maximum Segment Lifetime" [RFC0793]). This
is accomplished by the TIME-WAIT state and TCP's "quiet time" concept
(see Appendix B of [RFC1323]). Based on the assumption that ISNs are
monotonically increasing across connections, many stacks (e.g.,
4.2BSD-derived) use the ISN of an incoming SYN segment to perform
"heuristics" that enable the creation of a new incarnation of a
connection while the previous incarnation is still in the TIME-WAIT
state (see p. 945 of [Wright1994]). This avoids an interoperability
problem that may arise when a node establishes connections to a
specific TCP end-point at a high rate [Silbersack2005].
The interoperability requirements for TCP ISNs are probably not as
clearly spelled out as one would expect. Furthermore, the suggestion
of employing a global counter in [RFC0793] negatively affects the
security and privacy properties of the protocol.
September 1981:
[RFC0793], suggests the use of a global 32-bit ISN generator,
whose lower bit is incremented roughly every 4 microseconds.
However, such an ISN generator makes it trivial to predict the ISN
that a TCP instance will use for new connections, thus allowing a
variety of attacks against TCP.
February 1985:
[Morris1985] was the first to describe how to exploit predictable
TCP ISNs for forging TCP connections that could then be leveraged
for trust relationship exploitation.
April 1989:
[Bellovin1989] discussed the security considerations for
predictable ISNs (along with a range of other protocol-based
vulnerabilities).
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February 1995:
[Shimomura1995] reported a real-world exploitation of the attack
described in [Morris1985] ten years before (in 1985).
May 1996:
[RFC1948] was the first IETF effort, authored by Steven Bellovin,
to address predictable TCP ISNs. However, [RFC1948] does not
formally update [RFC0793]. The same concept specified in this
document for TCP ISNs was later proposed for TCP ephemeral ports
[RFC6056], TCP Timestamps, and eventually even IPv6 Interface
Identifiers [RFC7217].
July 1996:
OpenBSD implements TCP ISN randomization based on random
increments (please see Appendix A.2 of
[I-D.irtf-pearg-numeric-ids-generation]) [OpenBSD-TCP-ISN-I].
December 2000:
OpenBSD implements TCP ISN randomization using simple
randomization (please see Section 7.1 of
[I-D.irtf-pearg-numeric-ids-generation]) [OpenBSD-TCP-ISN-R].
March 2001:
[Zalewski2001] provides a detailed analysis of statistical
weaknesses in some ISN generators, and includes a survey of the
algorithms in use by popular TCP implementations.
May 2001:
Vulnerability advisories [CERT2001] [USCERT2001] were released
regarding statistical weaknesses in some ISN generators, affecting
popular TCP implementations.
March 2002:
[Zalewski2002] updates and complements [Zalewski2001]. It
concludes that "while some vendors [...] reacted promptly and
tested their solutions properly, many still either ignored the
issue and never evaluated their implementations, or implemented a
flawed solution that apparently was not tested using a known
approach" [Zalewski2002].
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June 2007:
OpenBSD implements TCP ISN randomization based on the algorithm
specified in [RFC1948] (currently obsoleted and replaced by
[RFC6528]) for the TCP endpoint that performs the active open,
while keeping the simple randomization scheme for the endpoint
performing the passive open [OpenBSD-TCP-ISN-H]. This provides
monotonically-increasing ISNs for the client side (allowing the
BSD heuristics to work as expected), while avoiding any patterns
in the ISN generation for the server side.
February 2012:
[RFC6528], published 27 years after Morris' original work
[Morris1985], formally updates [RFC0793] to mitigate predictable
TCP ISNs.
August 2014:
[I-D.eddy-rfc793bis-04], the upcoming revision of the core TCP
protocol specification, incorporates the algorithm specified in
[RFC6528] as the recommended ("SHOULD") algorithm for TCP ISN
generation.
4.3. IPv6 Interface Identifiers (IIDs)
IPv6 Interface Identifiers can be generated as a result of different
mechanisms, including SLAAC [RFC4862], DHCPv6 [RFC8415], and manual
configuration. This section focuses on Interface Identifiers
resulting from SLAAC.
The Interface Identifier of stable (traditional) IPv6 addresses
resulting from SLAAC have traditionally resulted in the underlying
link-layer address being embedded in the IID.At the time, employing
the underlying link-layer address for the IID was seen as a
convenient way to obtain a unique address. However, recent awareness
about the security and privacy properties of this approach [RFC7707]
[RFC7721] has led to the replacement of this flawed scheme with an
alternative one [RFC7217] [RFC8064] that does not negatively affect
the security and privacy properties of the protocol.
January 1997:
[RFC2073] specifies the syntax of IPv6 global addresses (referred
to as "An IPv6 Provider-Based Unicast Address Format" at the
time), consistent with the IPv6 addressing architecture specified
in [RFC1884]. Hosts are recommended to "generate addresses using
link-specific addresses as Interface ID such as 48 bit IEEE-802
MAC addresses".
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July 1998:
[RFC2374] specifies "An IPv6 Aggregatable Global Unicast Address
Format" (obsoleting [RFC2373]) changing the size of the IID to 64
bits, and specifies that IIDs must be constructed in IEEE EUI-64
format. How such identifiers are constructed becomes specified in
the corresponding "IPv6 over <link>" specifications, such as "IPv6
over Ethernet".
January 2001:
[RFC3041] recognizes the problem of network activity correlation,
and specifies temporary addresses. Temporary addresses are to be
used along with stable addresses.
August 2003:
[RFC3587] obsoletes [RFC2374], making the TLA/NLA structure
historic. The syntax and recommendations for the traditional
stable IIDs remain unchanged, though.
February 2006:
[RFC4291] is published as the latest "IP Version 6 Addressing
Architecture", requiring the IIDs of the traditional (stable) IPv6
addresses resulting from SLAAC to employ the Modified EUI-64
format. The details of constructing such interface identifiers
are defined in the corresponding "IPv6 over <link>"
specifications.
March 2008:
[RFC5157] provides hints regarding how patterns in IPv6 addresses
could be leveraged for the purpose of address scanning.
December 2011:
[draft-gont-6man-stable-privacy-addresses-00] notes that the
traditional scheme for generating stable addresses allows for
address scanning, and also does not prevent active node tracking.
It also specifies an alternative algorithm meant to replace IIDs
based on Modified EUI-64 format identifiers.
November 2012:
The 6man WG adopts [I-D.gont-6man-stable-privacy-addresses] as a
working group item (as
[draft-ietf-6man-stable-privacy-addresses-00]). However, the
document no longer formally updates [RFC4291], and therefore the
specified algorithm no longer formally replaces the Modified
EUI-64 format identifiers.
February 2013:
An address-scanning tool (scan6 of [IPv6-Toolkit]) that leverages
IPv6 address patterns is released [Gont2013].
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July 2013:
[I-D.cooper-6man-ipv6-address-generation-privacy] elaborates on
the security and privacy properties of all known algorithms for
generating IPv6 IIDs.
January 2014:
The 6man WG publishes [draft-ietf-6man-default-iids-00]
("Recommendation on Stable IPv6 Interface Identifiers"),
recommending [I-D.ietf-6man-stable-privacy-addresses] for the
generation of stable addresses.
April 2014:
[RFC7217] (formerly [I-D.ietf-6man-stable-privacy-addresses]) is
published, specifying "A Method for Generating Semantically Opaque
Interface Identifiers with IPv6 Stateless Address
Autoconfiguration (SLAAC)" as an alternative to (but *not*
replacement of) Modified EUI-64 format IIDs.
March 2016:
[RFC7707] (formerly [I-D.gont-opsec-ipv6-host-scanning], and later
[I-D.ietf-opsec-ipv6-host-scanning]), about "Network
Reconnaissance in IPv6 Networks", is published.
March 2016:
[RFC7721] (formerly
[I-D.cooper-6man-ipv6-address-generation-privacy] and later
[I-D.ietf-6man-ipv6-address-generation-privacy]), about "Security
and Privacy Considerations for IPv6 Address Generation
Mechanisms", is published.
May 2016:
[draft-gont-6man-non-stable-iids-00] is published, with the goal
of specifying requirements for non-stable addresses, and updating
[RFC4941] such that use of only temporary addresses is allowed.
May 2016:
[draft-gont-6man-address-usage-recommendations-00] is published,
providing an analysis of how different aspects on an address (from
stability to usage mode) affect their corresponding security and
privacy properties, and meaning to eventually provide advice in
this area.
February 2017:
The 6man WG publishes [RFC8064] ("Recommendation on Stable IPv6
Interface Identifiers") (formerly [I-D.ietf-6man-default-iids]),
with requirements for stable addresses and a recommendation to
employ [RFC7217] for the generation of stable addresses. It
formally updates a large number of RFCs.
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March 2018:
[draft-fgont-6man-rfc4941bis-00] is published (as suggested by the
6man WG), to address flaws in [RFC4941] by revising it (as an
alternative to the [draft-gont-6man-non-stable-iids-00] effort,
published in March 2016).
July 2018:
[draft-fgont-6man-rfc4941bis-00] is adopted (as
[draft-ietf-6man-rfc4941bis-00]) as a WG item of the 6man WG.
December 2020:
[I-D.ietf-6man-rfc4941bis] is approved by the IESG for publication
as an RFC.
February 2021:
[I-D.ietf-6man-rfc4941bis] is finally published as [RFC8981].
4.4. NTP Reference IDs (REFIDs)
The NTP [RFC5905] Reference ID is a 32-bit code identifying the
particular server or reference clock. Above stratum 1 (secondary
servers and clients), this value can be employed to avoid degree-one
timing loops; that is, scenarios where two NTP peers are (mutually)
the time source of each other. If using the IPv4 address family, the
identifier is the four-octet IPv4 address. If using the IPv6 address
family, it is the first four octets of the MD5 hash of the IPv6
address.
June 2010:
[RFC5905], "Network Time Protocol Version 4: Protocol and
Algorithms Specification" is published. It specifies that for NTP
peers with stratum higher than 1 the REFID embeds the IPv4 Address
of the time source or an MD5 hash of the IPv6 address of the time
source.
July 2016:
[draft-stenn-ntp-not-you-refid-00] is published, describing the
information leakage produced via the NTP REFID. It proposes that
NTP returns a special REFID when a packet employs an IP Source
Address that is not believed to be a current NTP peer, but
otherwise generates and returns the traditional REFID. It is
subsequently adopted by the NTP WG as
[I-D.ietf-ntp-refid-updates].
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April 2019:
[Gont-NTP] notes that the proposed fix specified in
[draft-ietf-ntp-refid-updates-00] is, at the very least, sub-
optimal. As a result of lack of WG support, the effort is
eventually abandoned.
4.5. Transport Protocol Ephemeral Port Numbers
Most (if not all) transport protocols employ "port numbers" to
demultiplex packets to the corresponding transport protocol
instances.
August 1980:
[RFC0768] notes that the UDP source port is optional and
identifies the port of the sending process. It does not specify
interoperability requirements for source port selection, nor does
it suggest possible ways to select port numbers. Most popular
implementations end up selecting source ports from a system-wide
global counter.
September 1981:
[RFC0793] (the TCP specification) essentially describes the use of
port numbers, and specifies that port numbers should result in a
unique socket pair (local address, local port, remote address,
remote port). How ephemeral ports (i.e. port numbers for "active
opens") are selected, and the port range from which they are
selected, are left unspecified.
July 1996:
OpenBSD implements ephemeral port randomization [OpenBSD-PR].
July 2008:
The CERT Coordination Centre published details of what became
known as the "Kaminsky Attack" [VU-800113] [Kaminsky2008] on the
DNS. The attack exploited the lack of source port randomization
in many major DNS implementations to perform cache poisoning in an
effective and practical manner.
January 2009:
[RFC5452] mandates the use of port randomization for DNS
resolvers, and mandates that implementations must randomize ports
from the range (53 or 1024, and above) or the largest possible
port range. It does not recommend possible algorithms for port
randomization, although the document specifically targets DNS
resolvers, for which a simple port randomization suffices (e.g.
Algorithm 1 of [RFC6056]). This document led to the
implementation of port randomization in the DNS resolver
themselves, rather than in the underlying transport-protocols.
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January 2011:
[RFC6056] notes that many TCP and UDP implementations result in
predictable port numbers, and also notes that many implementations
select port numbers from a small portion of the whole port number
space. It recommends the implementation and use of ephemeral port
randomization, proposes a number of possible algorithms for port
randomization, and also recommends to randomize port numbers over
the range 1024-65535.
March 2016:
[NIST-NTP] reports a non-normal distribution of the ephemeral port
numbers employed by the NTP clients of an Internet Time Service.
April 2019:
[I-D.gont-ntp-port-randomization] notes that some NTP
implementations employ the NTP service port (123) as the local
port for non-symmetric modes, and aims to update the NTP
specification to recommend port randomization in such cases, in
line with [RFC6056]. The proposal experiences some push-back in
the relevant working group (NTP WG) [NTP-PORTR], but is finally
adopted as a working group item as
[I-D.ietf-ntp-port-randomization].
August 2021:
[I-D.ietf-ntp-port-randomization] is finally published as
[RFC9109].
4.6. DNS Query ID
The DNS Query ID [RFC1035] can be employed to match DNS replies to
outstanding DNS queries.
November 1987:
[RFC1035] specifies that the ID is a 16 bit identifier assigned by
the program that generates any kind of query, and that this
identifier is copied in the corresponding reply and can be used by
the requester to match up replies to outstanding queries. It does
not specify the interoperability requirements for these numeric
identifiers, nor does it suggest an algorithm for generating them.
1993:
[Schuba1993] describes DNS cache poisoning attacks that require
the attacker to guess the Query ID.
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June 1995:
[Vixie1995] suggests that both the UDP source port and the ID of
query packets should be randomized, although that might not
provide enough entropy to prevent an attacker from guessing these
values.
April 1997:
[Arce1997] finds that implementations employ predictable UDP
source ports and predictable Query IDs, and argues that both
should be randomized.
November 2002:
[Sacramento2002] finds that by spoofing multiple requests for the
same domain name from different IP addresses, an attacker may
guess the Query ID employed for a victim with a high probability
of success, thus performing DNS cache poisoning attacks.
July 2007:
[Klein2007b] finds that a popular DNS server software (BIND 9)
that randomizes the Query ID is still subject to DNS cache
poisoning attacks by forging a large number of queries and
leveraging the birthday paradox.
March 2007:
[Klein2007c] finds that Microsoft Windows DNS Server generates
predictable Query ID values.
October 2007:
[Klein2007] finds that OpenBSD's DNS software (based on ISC's BIND
DNS Server) generates predictable Query ID values.
January 2009:
[RFC5452] is published, requiring resolvers to randomize the Query
ID of DNS queries, and to verify that the Query ID of a DNS reply
matches that of the DNS query as part of the DNS reply validation
process.
May 2010:
[Economou2010] finds that Windows SMTP Service implements its own
DNS resolver that results in predictable Query ID values.
Additionally, it fails to validate that the Query ID of DNS reply
matches the one from the DNS query that supposedly elicited the
reply.
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5. Conclusions
For more than 30 years, a large number of implementations of the IETF
protocols have been subject to a variety of attacks, with effects
ranging from Denial of Service (DoS) or data injection, to
information leakages that could be exploited for pervasive monitoring
[RFC7258]. The root cause of these issues has been, in many cases,
poor selection of transient numeric identifiers, usually as a result
of insufficient or misleading specifications.
While it is generally possible to identify an algorithm that can
satisfy the interoperability requirements for a given transient
numeric identifier, this document provides empirical evidence that
doing so without negatively affecting the security or privacy
properties of the aforementioned protocols is non-trivial. It is
thus evident that advice in this area is warranted.
[I-D.gont-numeric-ids-sec-considerations] aims at requiring future
IETF protocol specifications to contain analysis of the security and
privacy properties of any transient numeric identifiers specified by
the protocol, and to recommend an algorithm for the generation of
such transient numeric identifiers.
[I-D.irtf-pearg-numeric-ids-generation] specifies a number of sample
algorithms for generating transient numeric identifiers with specific
interorability requirements and failure severities.
6. IANA Considerations
There are no IANA registries within this document.
7. Security Considerations
This document analyzes the timeline of the specification and
implementation of the transient numeric identifiers of some sample
IETF protocols, and how the security and privacy properties of such
protocols have been affected as a result of it. It provides concrete
evidence that advice in this area is warranted.
[I-D.gont-numeric-ids-sec-considerations] formally requires IETF
protocol specifications to specify the interoperability requirements
for their transient numeric identifiers, to do a warranted
vulnerability assessment of such transient numeric identifiers, and
to recommend possible algorithms for their generation, such that the
interoperability requirements are complied with, while any negative
security and privacy properties of these transient numeric
identifiers are mitigated.
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[I-D.irtf-pearg-numeric-ids-generation] analyzes and categorizes
transient numeric identifiers based on their interoperability
requirements and their associated failure severities, and recommends
possible algorithms that can comply with those requirements without
negatively affecting the security and privacy properties of the
corresponding protocols.
8. Acknowledgements
The authors would like to thank (in alphabetical order) Bernard
Aboba, Dave Crocker, Spencer Dawkins, Theo de Raadt, Sara Dickinson,
Guillermo Gont, Christian Huitema, Colin Perkins, Vincent Roca, Kris
Shrishak, Joe Touch, Brian Trammell, and Christopher Wood, for
providing valuable comments on earlier versions of this document.
The authors would like to thank (in alphabetical order) Steven
Bellovin, Joseph Lorenzo Hall, Gre Norcie, and Martin Thomson, for
providing valuable comments on [I-D.gont-predictable-numeric-ids], on
which this document is based.
Section 4.2 of this document borrows text from [RFC6528], authored by
Fernando Gont and Steven Bellovin.
The authors would like to thank Sara Dickinson and Christopher Wood,
for their guidance during the publication process of this document.
The authors would like to thank Diego Armando Maradona for his magic
and inspiration.
9. References
9.1. Normative References
[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
DOI 10.17487/RFC0768, August 1980,
<https://www.rfc-editor.org/info/rfc768>.
[RFC0793] Postel, J., "Transmission Control Protocol", RFC 793,
DOI 10.17487/RFC0793, September 1981,
<https://www.rfc-editor.org/info/rfc793>.
[RFC6528] Gont, F. and S. Bellovin, "Defending against Sequence
Number Attacks", RFC 6528, DOI 10.17487/RFC6528, February
2012, <https://www.rfc-editor.org/info/rfc6528>.
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
DOI 10.17487/RFC0791, September 1981,
<https://www.rfc-editor.org/info/rfc791>.
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[RFC1883] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 1883, DOI 10.17487/RFC1883,
December 1995, <https://www.rfc-editor.org/info/rfc1883>.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
December 1998, <https://www.rfc-editor.org/info/rfc2460>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
[RFC7217] Gont, F., "A Method for Generating Semantically Opaque
Interface Identifiers with IPv6 Stateless Address
Autoconfiguration (SLAAC)", RFC 7217,
DOI 10.17487/RFC7217, April 2014,
<https://www.rfc-editor.org/info/rfc7217>.
[RFC3041] Narten, T. and R. Draves, "Privacy Extensions for
Stateless Address Autoconfiguration in IPv6", RFC 3041,
DOI 10.17487/RFC3041, January 2001,
<https://www.rfc-editor.org/info/rfc3041>.
[RFC2073] Rekhter, Y., Lothberg, P., Hinden, R., Deering, S., and J.
Postel, "An IPv6 Provider-Based Unicast Address Format",
RFC 2073, DOI 10.17487/RFC2073, January 1997,
<https://www.rfc-editor.org/info/rfc2073>.
[RFC2374] Hinden, R., O'Dell, M., and S. Deering, "An IPv6
Aggregatable Global Unicast Address Format", RFC 2374,
DOI 10.17487/RFC2374, July 1998,
<https://www.rfc-editor.org/info/rfc2374>.
[RFC3587] Hinden, R., Deering, S., and E. Nordmark, "IPv6 Global
Unicast Address Format", RFC 3587, DOI 10.17487/RFC3587,
August 2003, <https://www.rfc-editor.org/info/rfc3587>.
[RFC1884] Hinden, R., Ed. and S. Deering, Ed., "IP Version 6
Addressing Architecture", RFC 1884, DOI 10.17487/RFC1884,
December 1995, <https://www.rfc-editor.org/info/rfc1884>.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <https://www.rfc-editor.org/info/rfc4291>.
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[RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy
Extensions for Stateless Address Autoconfiguration in
IPv6", RFC 4941, DOI 10.17487/RFC4941, September 2007,
<https://www.rfc-editor.org/info/rfc4941>.
[RFC2373] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 2373, DOI 10.17487/RFC2373, July 1998,
<https://www.rfc-editor.org/info/rfc2373>.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862,
DOI 10.17487/RFC4862, September 2007,
<https://www.rfc-editor.org/info/rfc4862>.
[RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A.,
Richardson, M., Jiang, S., Lemon, T., and T. Winters,
"Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
RFC 8415, DOI 10.17487/RFC8415, November 2018,
<https://www.rfc-editor.org/info/rfc8415>.
[RFC1323] Jacobson, V., Braden, R., and D. Borman, "TCP Extensions
for High Performance", RFC 1323, DOI 10.17487/RFC1323, May
1992, <https://www.rfc-editor.org/info/rfc1323>.
[RFC6056] Larsen, M. and F. Gont, "Recommendations for Transport-
Protocol Port Randomization", BCP 156, RFC 6056,
DOI 10.17487/RFC6056, January 2011,
<https://www.rfc-editor.org/info/rfc6056>.
[RFC5452] Hubert, A. and R. van Mook, "Measures for Making DNS More
Resilient against Forged Answers", RFC 5452,
DOI 10.17487/RFC5452, January 2009,
<https://www.rfc-editor.org/info/rfc5452>.
9.2. Informative References
[OpenBSD-PR]
OpenBSD, "Implementation of port randomization", 29 July
1996, <https://cvsweb.openbsd.org/src/sys/netinet/
in_pcb.c?rev=1.6>.
[VU-800113]
CERT/CC, "Multiple DNS implementations vulnerable to cache
poisoning (Vulnerability Note VU#800113)", 8 July 2008,
<https://www.kb.cert.org/vuls/id/800113>.
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[IANA-PROT]
IANA, "Protocol Registries",
<https://www.iana.org/protocols>.
[RFC5157] Chown, T., "IPv6 Implications for Network Scanning",
RFC 5157, DOI 10.17487/RFC5157, March 2008,
<https://www.rfc-editor.org/info/rfc5157>.
[RFC8981] Gont, F., Krishnan, S., Narten, T., and R. Draves,
"Temporary Address Extensions for Stateless Address
Autoconfiguration in IPv6", RFC 8981,
DOI 10.17487/RFC8981, February 2021,
<https://www.rfc-editor.org/info/rfc8981>.
[I-D.ietf-6man-rfc4941bis]
Gont, F., Krishnan, S., Narten, T., and R. P. Draves,
"Temporary Address Extensions for Stateless Address
Autoconfiguration in IPv6", Work in Progress, Internet-
Draft, draft-ietf-6man-rfc4941bis-12, 2 November 2020,
<https://www.ietf.org/archive/id/draft-ietf-6man-
rfc4941bis-12.txt>.
[I-D.gont-opsec-ipv6-host-scanning]
Gont, F. and T. Chown, "Network Reconnaissance in IPv6
Networks", Work in Progress, Internet-Draft, draft-gont-
opsec-ipv6-host-scanning-02, 22 October 2012,
<https://www.ietf.org/archive/id/draft-gont-opsec-ipv6-
host-scanning-02.txt>.
[I-D.ietf-opsec-ipv6-host-scanning]
Gont, F. and T. Chown, "Network Reconnaissance in IPv6
Networks", Work in Progress, Internet-Draft, draft-ietf-
opsec-ipv6-host-scanning-08, 28 August 2015,
<https://www.ietf.org/archive/id/draft-ietf-opsec-ipv6-
host-scanning-08.txt>.
[I-D.gont-6man-stable-privacy-addresses]
Gont, F., "A method for Generating Stable Privacy-Enhanced
Addresses with IPv6 Stateless Address Autoconfiguration
(SLAAC)", Work in Progress, Internet-Draft, draft-gont-
6man-stable-privacy-addresses-01, 31 March 2012,
<https://www.ietf.org/archive/id/draft-gont-6man-stable-
privacy-addresses-01.txt>.
[I-D.ietf-6man-stable-privacy-addresses]
Gont, F., "A Method for Generating Semantically Opaque
Interface Identifiers with IPv6 Stateless Address
Autoconfiguration (SLAAC)", Work in Progress, Internet-
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Draft, draft-ietf-6man-stable-privacy-addresses-17, 27
January 2014, <https://www.ietf.org/archive/id/draft-ietf-
6man-stable-privacy-addresses-17.txt>.
[I-D.cooper-6man-ipv6-address-generation-privacy]
Cooper, A., Gont, F., and D. Thaler, "Privacy
Considerations for IPv6 Address Generation Mechanisms",
Work in Progress, Internet-Draft, draft-cooper-6man-ipv6-
address-generation-privacy-00, 15 July 2013,
<https://www.ietf.org/archive/id/draft-cooper-6man-ipv6-
address-generation-privacy-00.txt>.
[I-D.ietf-6man-ipv6-address-generation-privacy]
Cooper, A., Gont, F., and D. Thaler, "Security and Privacy
Considerations for IPv6 Address Generation Mechanisms",
Work in Progress, Internet-Draft, draft-ietf-6man-ipv6-
address-generation-privacy-08, 23 September 2015,
<https://www.ietf.org/archive/id/draft-ietf-6man-ipv6-
address-generation-privacy-08.txt>.
[Gont2013] Gont, F., "Beta release of the SI6 Network's IPv6 Toolkit
(help wanted!)", Message posted to the IPv6 Hackers
mailing-list Message-ID:
<51184548.3030105@si6networks.com>, 2013,
<https://lists.si6networks.com/pipermail/
ipv6hackers/2013-February/000947.html>.
[IPv6-Toolkit]
SI6 Networks, "SI6 Networks' IPv6 Toolkit",
<https://www.si6networks.com/tools/ipv6toolkit>.
[draft-gont-6man-stable-privacy-addresses-00]
Gont, F., "A method for Generating Stable Privacy-Enhanced
Addresses with IPv6 Stateless Address Autoconfiguration
(SLAAC)", Work in Progress, Internet-Draft, draft-gont-
6man-stable-privacy-addresses-00, 15 December 2011,
<https://tools.ietf.org/id/draft-gont-6man-stable-privacy-
addresses-00.txt>.
[draft-ietf-6man-stable-privacy-addresses-00]
Gont, F., "A method for Generating Stable Privacy-Enhanced
Addresses with IPv6 Stateless Address Autoconfiguration
(SLAAC)", Work in Progress, Internet-Draft, draft-ietf-
6man-stable-privacy-addresses-00, 18 May 2012,
<https://tools.ietf.org/id/draft-ietf-6man-stable-privacy-
addresses-00.txt>.
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[draft-gont-6man-address-usage-recommendations-00]
Gont, F. and W. Liu, "IPv6 Address Usage Recommendations",
Work in Progress, Internet-Draft, draft-gont-6man-address-
usage-recommendations-00, 27 May 2016,
<https://tools.ietf.org/id/draft-gont-6man-address-usage-
recommendations-00.txt>.
[draft-gont-6man-non-stable-iids-00]
Gont, F. and W. Liu, "Recommendation on Non-Stable IPv6
Interface Identifiers", Work in Progress, Internet-Draft,
draft-gont-6man-non-stable-iids-00, 23 May 2016,
<https://tools.ietf.org/id/draft-gont-6man-non-stable-
iids-00.txt>.
[draft-ietf-6man-default-iids-00]
Gont, F., Cooper, A., Thaler, D., and W. Liu,
"Recommendation on Stable IPv6 Interface Identifiers",
Work in Progress, Internet-Draft, draft-ietf-6man-default-
iids-00, 28 July 2014, <https://tools.ietf.org/id/draft-
ietf-6man-default-iids-00.txt>.
[RFC8064] Gont, F., Cooper, A., Thaler, D., and W. Liu,
"Recommendation on Stable IPv6 Interface Identifiers",
RFC 8064, DOI 10.17487/RFC8064, February 2017,
<https://www.rfc-editor.org/info/rfc8064>.
[draft-ietf-6man-rfc4941bis-00]
Gont, F., Krishnan, S.K., Narten, T.N., and R.D. Draves,
"Privacy Extensions for Stateless Address
Autoconfiguration in IPv6", Work in Progress, Internet-
Draft, draft-ietf-6man-rfc4941bis-00, 2 July 2018,
<https://tools.ietf.org/id/draft-ietf-6man-rfc4941bis-
00.txt>.
[draft-fgont-6man-rfc4941bis-00]
Gont, F., Krishnan, S.K., Narten, T.N., and R.D. Draves,
"Privacy Extensions for Stateless Address
Autoconfiguration in IPv6", Work in Progress, Internet-
Draft, draft-fgont-6man-rfc4941bis-00, 25 March 2018,
<https://tools.ietf.org/id/draft-fgont-6man-rfc4941bis-
00.txt>.
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[I-D.ietf-6man-default-iids]
Gont, F., Cooper, A., Thaler, D., and W. S. LIU,
"Recommendation on Stable IPv6 Interface Identifiers",
Work in Progress, Internet-Draft, draft-ietf-6man-default-
iids-16, 28 September 2016,
<https://www.ietf.org/archive/id/draft-ietf-6man-default-
iids-16.txt>.
[RFC7721] Cooper, A., Gont, F., and D. Thaler, "Security and Privacy
Considerations for IPv6 Address Generation Mechanisms",
RFC 7721, DOI 10.17487/RFC7721, March 2016,
<https://www.rfc-editor.org/info/rfc7721>.
[RFC7707] Gont, F. and T. Chown, "Network Reconnaissance in IPv6
Networks", RFC 7707, DOI 10.17487/RFC7707, March 2016,
<https://www.rfc-editor.org/info/rfc7707>.
[I-D.gont-predictable-numeric-ids]
Gont, F. and I. Arce, "Security and Privacy Implications
of Numeric Identifiers Employed in Network Protocols",
Work in Progress, Internet-Draft, draft-gont-predictable-
numeric-ids-03, 11 March 2019,
<https://www.ietf.org/archive/id/draft-gont-predictable-
numeric-ids-03.txt>.
[I-D.gont-numeric-ids-sec-considerations]
Gont, F. and I. Arce, "Security Considerations for
Transient Numeric Identifiers Employed in Network
Protocols", Work in Progress, Internet-Draft, draft-gont-
numeric-ids-sec-considerations-08, 10 December 2022,
<https://datatracker.ietf.org/api/v1/doc/document/draft-
gont-numeric-ids-sec-considerations/>.
[I-D.irtf-pearg-numeric-ids-generation]
Gont, F. and I. Arce, "On the Generation of Transient
Numeric Identifiers", Work in Progress, Internet-Draft,
draft-irtf-pearg-numeric-ids-generation-11, 11 July 2022,
<https://www.ietf.org/archive/id/draft-irtf-pearg-numeric-
ids-generation-11.txt>.
[I-D.ietf-6man-rfc2460bis]
Deering, S. E. and R. M. Hinden, "Internet Protocol,
Version 6 (IPv6) Specification", Work in Progress,
Internet-Draft, draft-ietf-6man-rfc2460bis-13, 19 May
2017, <https://www.ietf.org/archive/id/draft-ietf-6man-
rfc2460bis-13.txt>.
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[draft-stenn-ntp-not-you-refid-00]
Goldberg, S. and H. Stenn, "Network Time Protocol Not You
REFID", Work in Progress, Internet-Draft, draft-stenn-ntp-
not-you-refid-00, 8 July 2016, <https://tools.ietf.org/id/
draft-stenn-ntp-not-you-refid-00.txt>.
[draft-ietf-ntp-refid-updates-00]
Goldberg, S. and H. Stenn, "Network Time Protocol Not You
REFID", Work in Progress, Internet-Draft, draft-ietf-ntp-
refid-updates-00, 13 November 2016,
<https://tools.ietf.org/id/draft-ietf-ntp-refid-updates-
00.txt>.
[Gont-NTP] Gont, F., "[Ntp] Comments on draft-ietf-ntp-refid-updates-
05", Post to the NTP WG mailing list Message-ID:
<d871d66d-4043-d8d0-f924-2191ebb2e2ce@si6networks.com>, 16
April 2019, <https://mailarchive.ietf.org/arch/msg/ntp/
NkfTHxUUOdp14Agh3h1IPqfcRRg>.
[I-D.ietf-ntp-refid-updates]
Stenn, H. and S. Goldberg, "Network Time Protocol REFID
Updates", Work in Progress, Internet-Draft, draft-ietf-
ntp-refid-updates-05, 25 March 2019,
<https://www.ietf.org/archive/id/draft-ietf-ntp-refid-
updates-05.txt>.
[RFC5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
"Network Time Protocol Version 4: Protocol and Algorithms
Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010,
<https://www.rfc-editor.org/info/rfc5905>.
[RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an
Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May
2014, <https://www.rfc-editor.org/info/rfc7258>.
[RFC1948] Bellovin, S., "Defending Against Sequence Number Attacks",
RFC 1948, DOI 10.17487/RFC1948, May 1996,
<https://www.rfc-editor.org/info/rfc1948>.
[Wright1994]
Wright, G.R. and W.R. Stevens, "TCP/IP Illustrated, Volume
2: The Implementation", Addison-Wesley, 1994.
[Zalewski2001]
Zalewski, M., "Strange Attractors and TCP/IP Sequence
Number Analysis", 2001,
<https://lcamtuf.coredump.cx/oldtcp/tcpseq.html>.
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[Zalewski2002]
Zalewski, M., "Strange Attractors and TCP/IP Sequence
Number Analysis - One Year Later", 2001,
<https://lcamtuf.coredump.cx/newtcp/>.
[Bellovin1989]
Bellovin, S., "Security Problems in the TCP/IP Protocol
Suite", Computer Communications Review, vol. 19, no. 2,
pp. 32-48, 1989,
<https://www.cs.columbia.edu/~smb/papers/ipext.pdf>.
[Morris1985]
Morris, R., "A Weakness in the 4.2BSD UNIX TCP/IP
Software", CSTR 117, AT&T Bell Laboratories, Murray Hill,
NJ, 1985,
<https://pdos.csail.mit.edu/~rtm/papers/117.pdf>.
[USCERT2001]
US-CERT, "US-CERT Vulnerability Note VU#498440: Multiple
TCP/IP implementations may use statistically predictable
initial sequence numbers", 2001,
<https://www.kb.cert.org/vuls/id/498440>.
[CERT2001] CERT, "CERT Advisory CA-2001-09: Statistical Weaknesses in
TCP/IP Initial Sequence Numbers", 2001,
<https://resources.sei.cmu.edu/asset_files/
WhitePaper/2001_019_001_496192.pdf>.
[Shimomura1995]
Shimomura, T., "Technical details of the attack described
by Markoff in NYT", Message posted in USENET's
comp.security.misc newsgroup Message-ID:
<3g5gkl$5j1@ariel.sdsc.edu>, 1995,
<https://www.gont.com.ar/docs/post-shimomura-usenet.txt>.
[I-D.eddy-rfc793bis-04]
Eddy, W., "Transmission Control Protocol Specification",
Work in Progress, Internet-Draft, draft-eddy-rfc793bis-04,
25 August 2014,
<https://tools.ietf.org/id/draft-eddy-rfc793bis-04.txt>.
[OpenBSD-TCP-ISN-I]
OpenBSD, "Implementation of TCP ISN randomization based on
random increments", 29 July 1996,
<https://cvsweb.openbsd.org/src/sys/netinet/
tcp_subr.c?rev=1.6>.
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[OpenBSD-TCP-ISN-R]
OpenBSD, "Implementation of TCP ISN randomization based on
simple randomization", 13 December 2000,
<https://cvsweb.openbsd.org/src/sys/netinet/
tcp_subr.c?rev=1.37>.
[OpenBSD-TCP-ISN-H]
OpenBSD, "Implementation of RFC1948 for TCP ISN
randomization", 13 December 2000,
<https://cvsweb.openbsd.org/src/sys/netinet/
tcp_subr.c?rev=1.97>.
[I-D.gont-ntp-port-randomization]
Gont, F. and G. Gont, "Port Randomization in the Network
Time Protocol Version 4", Work in Progress, Internet-
Draft, draft-gont-ntp-port-randomization-04, 6 August
2019, <https://www.ietf.org/archive/id/draft-gont-ntp-
port-randomization-04.txt>.
[I-D.ietf-ntp-port-randomization]
Gont, F., Gont, G., and M. Lichvar, "Network Time Protocol
Version 4: Port Randomization", Work in Progress,
Internet-Draft, draft-ietf-ntp-port-randomization-08, 10
June 2021, <https://www.ietf.org/archive/id/draft-ietf-
ntp-port-randomization-08.txt>.
[RFC9109] Gont, F., Gont, G., and M. Lichvar, "Network Time Protocol
Version 4: Port Randomization", RFC 9109,
DOI 10.17487/RFC9109, August 2021,
<https://www.rfc-editor.org/info/rfc9109>.
[NTP-PORTR]
Gont, F., "[Ntp] New rev of the NTP port randomization I-D
(Fwd: New Version Notification for draft-gont-ntp-port-
randomization-01.txt)", 2019,
<https://mailarchive.ietf.org/arch/browse/
ntp/?gbt=1&index=n09Sb61WkH03lSRtamkELXwEQN4>.
[NIST-NTP] Sherman, J.A. and J. Levine, "Usage Analysis of the NIST
Internet Time Service", Journal of Research of the
National Institute of Standards and Technology Volume 121,
8 March 2016, <https://tf.nist.gov/general/pdf/2818.pdf>.
[IPID-DEV] Klein, A. and B. Pinkas, "From IP ID to Device ID and
KASLR Bypass (Extended Version)", June 2019,
<https://arxiv.org/pdf/1906.10478.pdf>.
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[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/info/rfc1035>.
[RFC6274] Gont, F., "Security Assessment of the Internet Protocol
Version 4", RFC 6274, DOI 10.17487/RFC6274, July 2011,
<https://www.rfc-editor.org/info/rfc6274>.
[RFC7739] Gont, F., "Security Implications of Predictable Fragment
Identification Values", RFC 7739, DOI 10.17487/RFC7739,
February 2016, <https://www.rfc-editor.org/info/rfc7739>.
[Bellovin2002]
Bellovin, S. M., "A Technique for Counting NATted Hosts",
IMW'02 Nov. 6-8, 2002, Marseille, France, 2002,
<https://www.cs.columbia.edu/~smb/papers/fnat.pdf>.
[Fyodor2002]
Fyodor, "Idle scanning and related IP ID games", 2002,
<http://www.insecure.org/nmap/idlescan.html>.
[Sanfilippo1998a]
Sanfilippo, S., "about the ip header id", Post to Bugtraq
mailing-list, Mon Dec 14 1998,
<http://seclists.org/bugtraq/1998/Dec/48>.
[Sanfilippo1998b]
Sanfilippo, S., "Idle scan", Post to Bugtraq mailing-list,
1998, <https://github.com/antirez/hping/raw/master/docs/
SPOOFED_SCAN.txt>.
[Sanfilippo1999]
Sanfilippo, S., "more ip id", Post to Bugtraq mailing-
list, 1999,
<https://github.com/antirez/hping/raw/master/docs/MORE-
FUN-WITH-IPID>.
[Morbitzer2013]
Morbitzer, M., "[PATCH] TCP Idle Scan in IPv6", Message
posted to the nmap-dev mailing-list, 2013,
<https://seclists.org/nmap-dev/2013/q2/394>.
[OpenBSD-IPv4-ID]
OpenBSD, "Randomization of the IPv4 Identification field",
26 December 1998,
<https://cvsweb.openbsd.org/src/sys/netinet/
ip_id.c?rev=1.1>.
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[OpenBSD-IPv6-ID]
OpenBSD, "Randomization of the IPv6 Identification field",
1 October 2003,
<https://cvsweb.openbsd.org/src/sys/netinet6/
ip6_id.c?rev=1.1>.
[Silbersack2005]
Silbersack, M.J., "Improving TCP/IP security through
randomization without sacrificing interoperability",
EuroBSDCon 2005 Conference, 2005,
<https://citeseerx.ist.psu.edu/viewdoc/
download?doi=10.1.1.91.4542&rep=rep1&type=pdf>.
[Zalewski2003]
Zalewski, M., "A new TCP/IP blind data injection
technique?", 2003,
<https://lcamtuf.coredump.cx/ipfrag.txt>.
[Arce1997] Arce, I. and E. Kargieman, "BIND Vulnerabilities and
Solutions", 1997,
<http://www.openbsd.org/advisories/sni_12_resolverid.txt>.
[Klein2007]
Klein, A., "OpenBSD DNS Cache Poisoning and Multiple O/S
Predictable IP ID Vulnerability", 2007,
<https://dl.packetstormsecurity.net/papers/attack/OpenBSD_
DNS_Cache_Poisoning_and_Multiple_OS_Predictable_IP_ID_Vuln
erability.pdf>.
[Gont2011] Gont, F., "Hacking IPv6 Networks (training course)", Hack
In Paris 2011 Conference Paris, France, June 2011.
[RedHat2011]
RedHat, "RedHat Security Advisory RHSA-2011:1465-1:
Important: kernel security and bug fix update", 2011,
<https://rhn.redhat.com/errata/RHSA-2011-1465.html>.
[Ubuntu2011]
Ubuntu, "Ubuntu: USN-1253-1: Linux kernel
vulnerabilities", 2011,
<https://ubuntu.com/security/notices/USN-1253-1>.
[SUSE2011] SUSE, "SUSE Security Announcement: Linux kernel security
update (SUSE-SA:2011:046)", 2011,
<https://lists.opensuse.org/opensuse-security-
announce/2011-12/msg00011.html>.
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[Gont2012] Gont, F., "Recent Advances in IPv6 Security", BSDCan 2012
Conference Ottawa, Canada. May 11-12, 2012, May 2012,
<https://www.si6networks.com/files/presentations/
bsdcan2012/fgont-bsdcan2012-recent-advances-in-
ipv6-security.pdf>.
[I-D.gont-6man-predictable-fragment-id]
Gont, F., "Security Implications of Predictable Fragment
Identification Values", Work in Progress, Internet-Draft,
draft-gont-6man-predictable-fragment-id-03, 9 January
2013, <https://www.ietf.org/archive/id/draft-gont-6man-
predictable-fragment-id-03.txt>.
[I-D.ietf-6man-predictable-fragment-id]
Gont, F., "Security Implications of Predictable Fragment
Identification Values", Work in Progress, Internet-Draft,
draft-ietf-6man-predictable-fragment-id-10, 9 October
2015, <https://www.ietf.org/archive/id/draft-ietf-6man-
predictable-fragment-id-10.txt>.
[draft-ietf-6man-predictable-fragment-id-01]
Gont, F., "Security Implications of Predictable Fragment
Identification Values", Work in Progress, Internet-Draft,
draft-ietf-6man-predictable-fragment-id-01, 30 April 2014,
<https://tools.ietf.org/id/draft-ietf-6man-predictable-
fragment-id-01.txt>.
[draft-ietf-6man-predictable-fragment-id-02]
Gont, F., "Security Implications of Predictable Fragment
Identification Values", Work in Progress, Internet-Draft,
draft-ietf-6man-predictable-fragment-id-02, 19 December
2014, <https://tools.ietf.org/id/draft-ietf-6man-
predictable-fragment-id-02.txt>.
[draft-gont-6man-predictable-fragment-id-00]
Gont, F., "Security Implications of Predictable Fragment
Identification Values", Work in Progress, Internet-Draft,
draft-gont-6man-predictable-fragment-id-00, 15 December
2011, <https://tools.ietf.org/id/draft-gont-6man-
predictable-fragment-id-00.txt>.
[draft-ietf-6man-predictable-fragment-id-00]
Gont, F., "Security Implications of Predictable Fragment
Identification Values", Work in Progress, Internet-Draft,
draft-ietf-6man-predictable-fragment-id-00, 22 March 2013,
<https://tools.ietf.org/id/draft-ietf-6man-predictable-
fragment-id-00.txt>.
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[draft-ietf-6man-predictable-fragment-id-08]
Gont, F., "Security Implications of Predictable Fragment
Identification Values", Work in Progress, Internet-Draft,
draft-ietf-6man-predictable-fragment-id-08, 9 June 2015,
<https://tools.ietf.org/id/draft-ietf-6man-predictable-
fragment-id-08.txt>.
[Schuba1993]
Schuba, C., "ADDRESSING WEAKNESSES IN THE DOMAIN NAME
SYSTEM PROTOCOL", 1993,
<http://ftp.cerias.purdue.edu/pub/papers/christoph-schuba/
schuba-DNS-msthesis.pdf>.
[Vixie1995]
Vixie, P., "DNS and BIND Security Issues", 5th Usenix
Security Symposium May 2, 1995, 2 May 1995, <https://www.u
senix.org/legacy/publications/library/proceedings/
security95/full_papers/vixie.pdf>.
[Klein2007b]
Klein, A., "BIND 9 DNS Cache Poisoning", March 2007,
<https://citeseerx.ist.psu.edu/viewdoc/
summary?doi=10.1.1.86.4474>.
[Klein2007c]
Klein, A., "Windows DNS Server Cache Poisoning", March
2007, <https://dl.packetstormsecurity.net/papers/attack/
Windows_DNS_Cache_Poisoning.pdf>.
[Sacramento2002]
Sacramento, V., "CAIS-ALERT: Vulnerability in the sending
requests control of BIND", 19 November 2002,
<https://seclists.org/bugtraq/2002/Nov/331>.
[Kaminsky2008]
Kaminsky, D., "Black Ops 2008: It's The End Of The Cache
As We Know It", August 2008,
<https://www.blackhat.com/presentations/bh-jp-08/bh-jp-08-
Kaminsky/BlackHat-Japan-08-Kaminsky-DNS08-BlackOps.pdf>.
[Economou2010]
Economou, N., "Windows SMTP Service DNS query Id
vulnerabilities", Advisory ID Internal CORE-2010-0427 May
4, 2010, 4 May 2010, <https://www.coresecurity.com/core-
labs/advisories/core-2010-0424-windows-smtp-dns-query-id-
bugs>.
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Authors' Addresses
Fernando Gont
SI6 Networks
Segurola y Habana 4310 7mo piso
Ciudad Autonoma de Buenos Aires
Buenos Aires
Argentina
Email: fgont@si6networks.com
URI: https://www.si6networks.com
Ivan Arce
Quarkslab
Segurola y Habana 4310 7mo piso
Ciudad Autonoma de Buenos Aires
Buenos Aires
Argentina
Email: iarce@quarkslab.com
URI: https://www.quarkslab.com
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