Internet DRAFT - draft-gont-numeric-ids-sec-considerations
draft-gont-numeric-ids-sec-considerations
Network Working Group F. Gont
Internet-Draft SI6 Networks
Updates: 3552 (if approved) I. Arce
Intended status: Best Current Practice Quarkslab
Expires: 31 July 2023 27 January 2023
Security Considerations for Transient Numeric Identifiers Employed in
Network Protocols
draft-gont-numeric-ids-sec-considerations-11
Abstract
Poor selection of transient numerical identifiers in protocols such
as the TCP/IP suite has historically led to a number of attacks on
implementations, ranging from Denial of Service (DoS) to data
injection and information leakage that can be exploited by pervasive
monitoring. Due diligence in the specification of transient numeric
identifiers is required even when cryptographic techniques are
employed, since these techniques might not mitigate all the
associated issues. This document formally updates RFC 3552,
incorporating requirements for transient numeric identifiers, to
prevent flaws in future protocols and implementations.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 31 July 2023.
Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
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license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Issues with the Specification of Transient Numeric
Identifiers . . . . . . . . . . . . . . . . . . . . . . . 5
4. Common Flaws in the Generation of Transient Numeric
Identifiers . . . . . . . . . . . . . . . . . . . . . . . 6
5. Requirements for Transient Numeric Identifiers . . . . . . . 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
9.1. Normative References . . . . . . . . . . . . . . . . . . 8
9.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
Network protocols employ a variety of transient numeric identifiers
for different protocol entities, ranging from DNS Transaction IDs
(TxIDs) to transport protocol numbers (e.g. TCP ports) or IPv6
Interface Identifiers (IIDs). These identifiers usually have
specific properties that must be satisfied such that they do not
result in negative interoperability implications (e.g., uniqueness
during a specified period of time), and an associated failure
severity when such properties are not met.
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The TCP/IP protocol suite alone has been subject to variety of
attacks on its transient numeric identifiers over the past 30 years
or more, with effects ranging from Denial of Service (DoS) or data
injection, to information leakage that could be exploited for
pervasive monitoring [RFC7258]. The root of these issues has been,
in many cases, the poor selection of identifiers in such protocols,
usually as a result of insufficient or misleading specifications.
While it is generally trivial to identify an algorithm that can
satisfy the interoperability requirements for a given identifier,
there exists practical evidence [I-D.irtf-pearg-numeric-ids-history]
that doing so without negatively affecting the security and/or
privacy properties of the aforementioned protocols is prone to error.
For example, implementations have been subject to security and/or
privacy issues resulting from:
* Predictable TCP sequence numbers (see e.g. [Morris1985],
[Bellovin1989], and [RFC6528])
* Predictable transport protocol numbers (see e.g. [Silbersack2005]
and [RFC6056])
* Predictable IPv4 or IPv6 Fragment Identifiers (see e.g.
[Sanfilippo1998a], [RFC6274], and [RFC7739])
* Predictable IPv6 IIDs (see e.g. [RFC7217], [RFC7707], and
[RFC7721])
* Predictable DNS TxIDs (see e.g. [Schuba1993] and [Klein2007])
Recent history indicates that when new protocols are standardized or
new protocol implementations are produced, the security and privacy
properties of the associated identifiers tend to be overlooked and
inappropriate algorithms to generate such identifiers are either
suggested in the specification or selected by implementers. As a
result, advice in this area is warranted.
We note that the use of cryptographic techniques for confidentiality
and authentication might not eliminate all the issues associated with
predictable transient numeric identifiers. Therefore, due diligence
in the specification of transient numeric identifiers is required
even when cryptographic techniques are employed.
Note:
For example, cryptographic authentication can readily mitigate
data injection attacks even in the presence of predictable
transient numeric identifiers (such as "sequence numbers").
However, use of flawed algorithms (such as global counters) for
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generating transient numeric identifiers could still result in
information leakages even when cryptographic techniques are
employed. These information leakages could in turn be leveraged
to perform other devastating attacks (please see
[I-D.irtf-pearg-numeric-ids-generation] for further details).
Section 3 provides an overview of common flaws in the specification
of transient numeric identifiers. Section 4 provides an overview of
the implications of predictable transient numeric identifiers.
Finally, Section 5 provides key guidelines for protocol designers.
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.
Failure Severity:
The interoperability consequences of a failure to comply with the
interoperability requirements of a given identifier. Severity
considers the worst potential consequence of a failure, determined
by the system damage and/or time lost to repair the failure. In
this document we define two types of failure severity: "soft" and
"hard".
Hard Failure:
A hard failure is a non-recoverable condition in which a protocol
does not operate in the prescribed manner or it operates with
excessive degradation of service. For example, an established TCP
connection that is aborted due to an error condition constitutes,
from the point of view of the transport protocol, a hard failure,
since it enters a state from which normal operation cannot be
recovered.
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Soft Failure:
A soft failure is a recoverable condition in which a protocol does
not operate in the prescribed manner but normal operation can be
resumed automatically in a short period of time. For example, a
simple packet-loss event that is subsequently recovered with a
retransmission can be considered a soft failure.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Issues with the Specification of Transient Numeric Identifiers
A recent survey of transient numeric identifier usage in protocol
specifications and implementations
[I-D.irtf-pearg-numeric-ids-history] revealed 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 identifiers
* Protocol specifications that over-specify their identifiers
* Protocol implementations that simply fail to comply with the
specified requirements
Both under-specifying and over-specifying identifiers is hazardous.
TCP port numbers and sequence numbers [RFC0793] and DNS TxID
[RFC1035] were originally under-specified, leading to implementations
that used predictable values and thus were vulnerable to numerous
off-path attacks. Over-specification, as for IPv6 Interface
Identifiers (IIDs) [RFC4291] and Fragment Identification values
[RFC2460], left implementations unable to respond to security and
privacy issues stemming from the mandated algorithms -- IPv6 IIDs
need not expose privacy-sensitive link-layer addresses, and
predictable Fragment Identifiers invite the same off-path attacks
that plague TCP.
Finally, there are protocol implementations that simply fail to
comply with existing protocol specifications. That is, appropriate
guidance is provided by the protocol specification (whether the core
specification or an update to it), but an implementation simply fails
to follow such guidance. For example, some popular operating systems
still fail to implement transport-protocol port randomization, as
specified in [RFC6056].
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Clear specification of the interoperability requirements for the
transient numeric identifiers will help identify possible algorithms
that could be employed to generate them, and also make evident if
such identifiers are being over-specified. A protocol specification
will usually also benefit from a vulnerability assessment of the
transient numeric identifiers they specify, to prevent the
corresponding considerations from being overlooked.
4. Common Flaws in the Generation of Transient Numeric Identifiers
This section briefly notes common flaws associated with the
generation of transient numeric identifiers. Such common flaws
include, but are not limited to:
* Employing trivial algorithms (e.g. global counters) that result in
predictable identifiers
* Employing the same identifier across contexts in which constancy
is not required
* Re-using identifiers across different protocols or layers of the
protocol stack
* Initializing counters or timers to constant values, when such
initialization is not required
* Employing the same increment space across different contexts
* Use of flawed pseudo-random number generators (PRNGs).
Employing trivial algorithms for generating the identifiers means
that any node that is able to sample such identifiers can easily
predict future identifiers employed by the victim node.
When one identifier is employed across contexts where such constancy
is not needed, activity correlation is made possible. For example,
employing an identifier that is constant across networks allows for
node tracking across networks.
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Re-using identifiers across different layers or protocols ties the
security and privacy properties of the protocol re-using the
identifier to the security and privacy properties of the original
identifier (over which the protocol re-using the identifier may have
no control regarding its generation). Besides, when re-using an
identifier across protocols from different layers, the goal of
isolating the properties of a layer from that of another layer is
broken, and the vulnerability assessment may be harder to perform,
since the combined system, rather than each protocol in isolation
will have to be assessed.
At times, a protocol needs to convey order information (whether
sequence, timing, etc.). In many cases, there is no reason for the
corresponding counter or timer to be initialized to any specific
value e.g. at system bootstrap. Similarly, there may not be a need
for the difference between successive counted values to be a
predictable.
A node that implements a per-context linear function may share the
increment space among different contexts (please see the "Simple
Hash-Based Algorithm" in [I-D.irtf-pearg-numeric-ids-generation]).
Sharing the same increment space allows an attacker that can sample
identifiers in other context to e.g. learn how many identifiers have
been generated between two sampled values.
Finally, some implementations have been found to employ flawed PRNGs
(see e.g. [Klein2007]).
5. Requirements for Transient Numeric Identifiers
Protocol specifications that employ transient numeric identifiers
MUST explicitly specify the interoperability requirements for the
aforementioned transient numeric identifiers (e.g., required
properties such as uniqueness, along with the failure severity if
such properties are not met).
A vulnerability assessment of the aforementioned transient numeric
identifiers MUST be performed as part of the specification process.
Such vulnerability assessment should cover, at least, spoofing,
tampering, repudiation, information disclosure, denial of service,
and elevation of privilege.
Note: Section 8 and Section 9 of
[I-D.irtf-pearg-numeric-ids-generation] provide a general
vulnerability assessment of transient numeric identifiers, along
with a vulnerability assessment of common algorithms for
generating transient numeric identifiers. Please see
[Shostack2014] for further guidance on threat modelling.
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Protocol specifications SHOULD NOT employ predictable transient
numeric identifiers, except when such predictability is the result of
their interoperability requirements.
Protocol specifications that employ transient numeric identifiers
SHOULD recommend an algorithm for generating the aforementioned
transient numeric identifiers that mitigates the vulnerabilities
identified in the previous step, such as those discussed in
[I-D.irtf-pearg-numeric-ids-generation].
As discussed in Section 1, use of cryptographic techniques for
confidentiality and authentication might not eliminate all the issues
associated with predictable transient numeric identifiers.
Therefore, the advice from this section MUST still be applied for
cases where cryptographic techniques are employed for confidentiality
or authentication of the associated transient numeric identifiers.
6. IANA Considerations
There are no IANA registries within this document.
7. Security Considerations
This entire document is about the security and privacy implications
of transient numeric identifiers, and formally updates [RFC3552] such
that the security and privacy implications of transient numeric
identifiers are addressed when writing the "Security Considerations"
section of future RFCs.
8. Acknowledgements
The authors would like to thank Bernard Aboba, Brian Carpenter, Roman
Danyliw, Theo de Raadt, Lars Eggert, Russ Housley, Benjamin Kaduk,
Charlie Kaufman, Erik Kline, Alvaro Retana, Joe Touch, Michael
Tuexen, Robert Wilton, and Paul Wouters, 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, for providing valuable
comments on [I-D.gont-predictable-numeric-ids] , on which the present
document is based.
The authors would like to thank Diego Armando Maradona for his magic
and inspiration.
9. References
9.1. Normative References
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC
Text on Security Considerations", BCP 72, RFC 3552,
DOI 10.17487/RFC3552, July 2003,
<https://www.rfc-editor.org/info/rfc3552>.
9.2. Informative References
[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>.
[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>.
[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>.
[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>.
[Sanfilippo1998a]
Sanfilippo, S., "about the ip header id", Post to Bugtraq
mailing-list, Mon Dec 14 1998,
<https://seclists.org/bugtraq/1998/Dec/48>.
[RFC0793] Postel, J., "Transmission Control Protocol", RFC 793,
DOI 10.17487/RFC0793, September 1981,
<https://www.rfc-editor.org/info/rfc793>.
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[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>.
[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>.
[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>.
[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>.
[Silbersack2005]
Silbersack, M.J., "Improving TCP/IP security through
randomization without sacrificing interoperability",
EuroBSDCon 2005 Conference, 2005,
<http://www.silby.com/eurobsdcon05/
eurobsdcon_silbersack.pdff>.
[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>.
[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>.
[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>.
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[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>.
[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>.
[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>.
[Shostack2014]
Shostack, A., "Threat Modeling: Designing for Security",
Wiley, 1st edition, 2014.
[I-D.irtf-pearg-numeric-ids-history]
Gont, F. and I. Arce, "Unfortunate History of Transient
Numeric Identifiers", Work in Progress, Internet-Draft,
draft-irtf-pearg-numeric-ids-history-11, 11 December 2022,
<https://www.ietf.org/archive/id/draft-irtf-pearg-numeric-
ids-history-11.txt>.
[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-12, 11 December
2022, <https://www.ietf.org/archive/id/draft-irtf-pearg-
numeric-ids-generation-12.txt>.
[IANA-PROT]
IANA, "Protocol Registries",
<https://www.iana.org/protocols>.
Authors' Addresses
Fernando Gont
SI6 Networks
Segurola y Habana 4310 7mo piso
Ciudad Autonoma de Buenos Aires
Buenos Aires
Argentina
Email: fgont@si6networks.com
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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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