| SFC Working Group | D. Migault, Ed. |
| Internet-Draft | Ericsson |
| Intended status: Informational | C. Pignataro |
| Expires: April 21, 2016 | T. Reddy |
| Cisco | |
| C. Inacio | |
| CERT/SEI/CMU | |
| October 19, 2015 |
SFC environment Security requirements
draft-mglt-sfc-security-environment-req-00.txt
This document provides environment security requirements for the SFC architecture. Environment security requirements are independent of the protocols used for SFC – such as NSH for example. As a result, the requirements provided in this document are intended to provide good security practices so SFC can be securely deployed and operated. These security requirements are designated as environment security requirements as opposed to the protocol security requirements.
This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 21, 2016.
Copyright (c) 2015 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 (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].
This document provides environment security requirements for the SFC architecture [I-D.ietf-sfc-architecture]. Environment security requirements are independent of the protocols used for SFC – such as NSH [I-D.ietf-sfc-nsh]. As a result, the requirements provided in this document are intended to provide good security practice so SFC can be securely deployed and operated. These security requirements are designated as environment security requirements as opposed to the protocol security requirements. This document is built as follows. Section [SFC Environment Overview] provides an overall description of the SFC environment with the introduction of the different planes (SFC Control Plane, the SFC Management Plane, the Tenant’s user Plane and the SFC Data Plane). Section [Threat Analysis] describes potential threats to the SFC architecture. Section [Plane Isolation] provides recommendations to limit the attack surface for outsider’s attacks. More specifically, it describes how to contain the SFC Data Plane and control access to the SFC Control(?) Plane outside of the SFC Data Plane. Section [SFC Data Plane Requirements] provides recommendations and requirements on how to limit the attack surface for an attacker inside the SFC Data Plane.
This document assumes the reader is familiar with the SFC architecture defined in [I-D.ietf-sfc-architecture].
This section provides an overview of SFC. It is not in the scope to this document to provide an explicit description of SFC. Instead, the reader is expected to read [I-D.ietf-sfc-architecture], [I-D.ietf-sfc-control-plane] and other SFC related documents.
Service Function Chaining (SFC) architecture is defined in [I-D.ietf-sfc-architecture]. This section briefly illustrates the main concepts of the SFC architecture and positions the architecture within an environment.
SFC Control Plane
^ ^ ^
-------------------------|---------------|-------------|----|--------
| C1 | C3 | C2 | | C4
| | +-----+ | |
| | | SF | | |
| | +-----+ | |
| v | | |
| +------------+ +-----+ +-----+ |
| +->| SFC |---->| SFF |----->| SFF |------+
SFC | | | Classifier |<----| |<-----| | | |
Management | | +------------+ +-----+ +-----+ | |
Plane | | ^ | | |
| | | +-----------+ |
| | | | SFC Proxy | |
| | | +-----------+ |
| | | | |
| | | +------+ |
| | v | SF | |
| | +---------+ +------+ |
| | | SFC 2 | <------------ SFC 1 -------> |
| | +---------+ |
| | SFC Data Plane |
-----------------|-----------------------------------------------|--
SFC incoming | SFC outgoing |
Data traffic | Data traffic v
SFC Tenant’s Users Data Plane
SFC Environment Overview
SFC defined a Service Function Path (SFP) which is an ordered set of Service Functions (SF) applied to packets. SFP is defined at the SF level. A SF may be performed by different instances of SF located at different positions. As a result, a specific packet may pass through different instances of SFC. The ordered set of SF instances a packet goes through is called the Rendered SF Path (RSFP).
Upon the receipt of an incoming packet from the tenant’s user, the SFC Classifier determines, according to Classifiers, which SFP is associated to that packet. The packet is forwarded from Service Function Forwarders (SFF) to SFF. SFF are then in charge of forwarding the packet to the next SFF or to a SF. Forwarding decisions may be performed using SFP information provided by the SFC Encapsulation. As described in [I-D.ietf-sfc-nsh] the SFC Encapsulation contains SFP information such as the SFP ID and Service Index and eventually (especially for the MD-2 in NSH) some additional metadata. SF may be SFC aware or not. In the case the SFC functions are not SFC aware, a SFC Proxy performs the SFC Decapsulation (resp. SFC Encapsulation) before forwarding the packet to the SF (resp. after receiving the packet from the SF).
The environment associated to SFC may be separated into three main planes:
This section describes potential threats the SFC Data Plane may be exposed. The list of threats is not expected to be complete.
Attacks may be performed from inside the SFC Data Plane or from outside the SFC Data plane, in which case, the attacker is in at least one of the following planes: SFC Control Plane, SFC Management Plane or SFC Tenants’ Users Plane. Some most sophisticated attacks may involve a coordination of attackers in multiple planes.
Attacks related to the control plane have been detailed in section 5 of [I-D.ietf-sfc-control-plane].
Attacks performed on the SFC Management Plane are similar to those performed from the SFC Control Plane. The main difference is that the SFC Management Plan provides usually a greater control of the SFC component that the SFC Control Plane.
In addition, the actions performed by the SFC Management Plane have fewer restrictions, which means it may be harder to enforce strong control access policies.
The SFC Tenant’s User Plane is not expected to have fine access control policies on the packets sent or received by users. Unless they are filtered, all packets are good candidate to the SFC Classifier. This provides the user some opportunities to test the behavior of the SFC.
In addition, the Tenant’s Users Plane is not controlled by the SFC Tenant, and users may initiate communications where both ends – the client and the server- are under the control of the same user. Such communications may be seen as user controlled communications (UCC).
UCC may enable any user to monitor and measure the health of the SFC. This may be an useful information to infer information on the tenant’s activity or to define when a DoS attack may cause more damage. One way to measure the health or load of the tenant’s SFC is to regularly send a packet and measure the time it takes to be received, in order to estimate the processing time within the SFC.
UCC may enable any user to test the consistency of the SFC. One example of inconsistency could be that SFC decapsulation is not performed – or inconsistently performed - before leaving the SFC, which could leak some metadata with private information. For example, a user may send spoofed packet. Suppose for example, that a request HTTP GET video.example.com/movie is received with some extra header information such as CLIENT_ID: 1234567890, or CLIENT_EMAIL: client@example.foo. If these pieces of information are derived from the source IP address, the attacker may collect them by changing the IP address for example. In this case, the spoofed packets as used to collect private and confidential information of the tenant’s users. Note that such threat is not specific to SFC, and results from the combination of spoofed IP and non-authenticated IP address are used to identify a user. What is specific to SFC is that metadata are likely to carry multiple pieces of information - potentially non-authenticated - associated to the user. In the case above, meta-data is carried over the HTTP header. Inserting the metadata in the HTTP header may be performed by a SF that takes its input from the SFC encapsulation. In addition, SFC encapsulation may also leak this information directly to a malicious node if that node belongs to the SFC plane. In this later case, the user builds on the top of and intrusion to the SFC Data Plane that is detailed later.
In some case, spoofed packet may impersonate other’s tenants. Suppose for example that the same infrastructure is used by multi tenants, and which are identified by the IP address of their users. In this case, spoofing an IP address associated to another tenant may be sufficient to collect the information confidential and private information.
Similarly, UCC may enable any user to infer packet has been dropped or is in a loop. Suppose a user send a spoofed packet and receives no response. The attacker may infer that the packet has been dropped or is in a loop. A loop is expect to load the system and sending a “well known packet” over the UCC and measuring the response time may determine whether the packet has been dropped or is in a loop.
Correlation of time measurement and spoofed packet over a UCC may provide various type information that could be used by an attacker.
Time measurement and spoofed packet in combination with variable query rate over a UCC may provide information on the orchestration of the SFC itself. For example, the user may be able to detect when elasticity mechanisms are triggered.
An attacker may be able to leverage the knowledge that SFC is in use by specific carriers to effect the processing of data using the SFC system as a processor in the attack. This leads to a number of potential weaknesses in the Internet ecosystem.
An attacker may be able to characterize the type of client platforms using a web site by carefully crafting data streams that will be modified by the SFC system versus client systems that would view web data unmodified. For example, leveraging SFC and carefully crafted data, a malicious web site operator may be able to create a particularly formatted common file that when modified by a cellular operator for bandwidth savings creates a file that may crash, (creating a DoS attack) on a select set of clients. Clients not accessing that web site using the same RSFP would not experience any issues. Additionally, external examination of the malicious site would not demonstrate any malicious content, relying on the SF to modify the content.
A well crafted site could potentially leverage the variances of functionality from different RSFPs in order to GEO locate a user. An example would be creating an image file which when recompressed creates image artifacts rendering the image unusable, but allowing the user to respond to such an event, thereby letting the web site operator know the user has potentially moved from a higher to lower bandwidth network location within the area of a specific network operator.
This section considers an attacker has been able to take control of an SFC component. As a result, the attacker may become able to modify the traffic and perform, on-path attacks, it may also be able to generate traffic, or redirect traffic to perform some kind of Man-in-the-middle attacks. This is clearly a fault, and security policies should be set to avoid this situation. This section analyses in case this intrusion occurs, the potential consequences on the SFC.
The traffic within the SFC Data Plane is composed of multiple layers. The traffic is composed of communications between SFC components. The transport between the SFC component is the transport protocol and is not considered in the SFC. It can typically be a L2 transport layer, or an L3 transport layer using various encapsulation techniques (vLAN, VxLAN, GRE, IPsec tunnels for example). The transport layer carries SFC Encapsulated that are composed of an SFC Encapsulation envelope that carries metadata and a SFC payload that is the actual packet exchanged between the two end points.
As a result, attacker may use the traffic to perform attacks at various layers. More specifically, attacks may be performed at the transport layer, the SFC Encapsulation layer or the SFC payload layer.
When an attacker is within the SFC Data Plane, it may have a full or partial control of one SF component in which case, the attacker is likely to compromise the associated SFCs. It could for example, modify the expected operation of the SFC. Note that in this case, the SFC may be appropriately provisioned and set, however, the SFC does not operate as expected this may only be detected by monitoring and auditing the SFC Data Plane.
Although traffic authentication may be performed at various layers L2 L3 or at the SFC Encapsulation layer, this section considers the SFC traffic. As a result, the SFC traffic is authenticated if the SF is able to authenticate the incoming SFC packet.
When SFC traffic is not authenticated, an attacker may inject spoofed packet in any SFC component. The attacker may use spoofed packet to discover the logic of the SFC. On the other hand, the attacker may also inject packet in order to perform DoS attack via reflection. In fact, some SF may carry large metadata, which may provide a vector for amplification within the SFC Data Plane and thus either load the network or the next SF. Note that amplification may be generated by metadata, the SFC payload, and the attacker may replay packets or completely craft new packets. In addition, the attacker may choose a spoofed packet to increase the CPU load on the SFC components. For example, it could insert additional metadata to generate fragmentation. Similarly, it may also insert unnecessary metadata that may need to be decapsulated and analyzed even though they may not be considered for further actions. Spoofed packet may not only be generated to attack the SFC component at the SFC layer. In fact spoofed packet may also target applications of the SF. For example an attacker may also forge packet for HTTP based application – like a L7 firewall – in order to perform a slowloris [SLOWLORIS] like attack. Note that in this case, such attacks are addressed in the Tenant’s Users Data Plane section. The specificity here is that the attacker has a more advanced understanding of the processing of the SFC, and can thus be more efficient.
When SFC traffic is not authenticated, an attacker may also modify on-path the packet. By changing some metadata contained in the SFC Encapsulation, the attacker may test and discover the logic of the SFF. Similarly, when the attacker is aware of the logic of a SFC component, the attacker may modify some metadata in order to modify the expected operation of the SFC. Such example includes for example redirection to a SF which could result in overloading the SF and overall affect the complete SFC. Similarly, the attacker may also create loops within the SFC. Note that redirection may not occur only in a given SFC. In fact, the attacker may use SFC branching to affect other SFC. Another example would also include a redirection to a node owned by the attacker and which is completely outside the SFC. Motivation for such redirection would be that the attacker has full administrator privileges on that node, whereas it only has limited capabilities on the corrupted node. Such attack is a man-in-the-middle attack. The important thing to note is that in this case the traffic is brought outside the legitimate SFC domain. In fact, performing a man-in-the-middle attack as described above means that the SFC domain has been extended. This can be easily performed in case all node of the data center or the tenant’s virtual network is likely to host a SFC component. A similar scenario may also consider that the traffic could be redirected outside the data center or the tenant’s virtual network if the routing of firewall rule enables such policies.
A direct consequence is that a corrupted SFC component may affect the whole SFC. This also means that the trust of a given SFC decreases with the number of SF involved as each SF presents a surface of attack.
An attacker may also perform passive attacks by listening to traffic exchanged throughout the SFC Data Plane. Such attacks are described in [RFC7258]. Metadata are associated to each packet. These metadata are additional pieces of information not carried in the packet and necessary for each SF to operate. As a result, metadata may contain private information such as identifiers or credentials. In addition, observing the traffic may provide information on the tenant’s activity. Note that encryption only may not prevent such attacks, as activity may be inferred by the traffic load.
Plane Isolation consists in limiting the surface of attack of the SFC Data Plane by controlling the interfaces between the SFC Data Plane and the other planes.
Complete isolation of the planes is not possible, as there are still some communications that must be enabled in order to benefit from the benefits of SFC. As a result, isolation should be understood as enabling communications between planes in a controlled way.
This section lists the recommendations so communication between planes can be controlled. This involves controlling communications between planes as well as controlling communication within a plane.
The requirements listed below applies to all planes, whereas the following subsection are more specific to each plane, providing recommendations on the interface with the SFC Data Plane.
In order to limit the risks of an attack from the SFC Control Plane, effort should be made in order to restrict the capabilities and the information provided by the SFC Data Plane to the SFC Control Plane to the authorized tenants only. In this case the authorized tenants are the users or organizations responsible for the SFC domain.
When possible, the use of API is recommended in order to limit the scope of possible interactions between the SFC Control Plane and the SFC Data Plane. This is one way to limit the possibilities of the tenants. In addition, each of these actions should be associated an authorized tenant, as well as authorized parameters.
The requirements for the SFC Control Plane and SFC Management Plane are similar. The main difference of the interfaces between the SFC Management Plane and the SFC Control Plane is that it is less likely that APIs could be used to configure the different SFC components. As a result, users of the SFC Management Plane are likely to have a broader and wider control over the SFC component.
The Tenant’s Users Data Plane is supposed to have less restricted access control than the other SFC Management Plane and SFC Control Planes. A typical use case could be that each tenant are controlling and managing the SFC in order to provide services to their associated users. The number of users interacting with the SFC Data Plane is expected to be larger than the number of tenants interacting with the SFC Control and SFC Management Planes. In addition, the scope of communications initiated or terminating at the user end points is likely to be unlimited compared to the scope of communications between the tenants and the SFC Control Plane or SFC Management Plane. In such cases, the tenant may be provided two roles. One to grant access to the SFC, and another one to control and manage the SFC. These two roles should be able to interact and communicate.
This section provides requirements and recommendation for the SFC Data Plane.
In addition, the following operational requirements have been identified:
The authors would like to thank Joel Halpern for his valuable comments.
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997. |
| [RFC6959] | McPherson, D., Baker, F. and J. Halpern, "Source Address Validation Improvement (SAVI) Threat Scope", RFC 6959, DOI 10.17487/RFC6959, May 2013. |
| [RFC7258] | Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May 2014. |
| [I-D.ietf-sfc-nsh] | Quinn, P. and U. Elzur, "Network Service Header", Internet-Draft draft-ietf-sfc-nsh-01, July 2015. |
| [I-D.ietf-sfc-architecture] | Halpern, J. and C. Pignataro, "Service Function Chaining (SFC) Architecture", Internet-Draft draft-ietf-sfc-architecture-11, July 2015. |
| [I-D.ietf-sfc-control-plane] | Li, H., Wu, Q., Huang, O., Boucadair, M., Jacquenet, C., Haeffner, W., Lee, S., Parker, R., Dunbar, L., Malis, A., Halpern, J., Reddy, T. and P. Patil, "Service Function Chaining (SFC) Control Plane Components & Requirements", Internet-Draft draft-ietf-sfc-control-plane-00, August 2015. |
| [SLOWLORIS] | Wikipedia, "Slowloris" |