Unfortunate History of Transient Numeric Identifiers
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|Authors||Fernando Gont , Ivan Arce|
|Replaced by||draft-irtf-pearg-numeric-ids-history, RFC 9414|
|Stream||Stream state||(No stream defined)|
|RFC Editor Note||(None)|
|IESG||IESG state||I-D Exists|
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Network Working Group F. Gont Internet-Draft SI6 Networks / UTN-FRH Intended status: Informational I. Arce Expires: January 9, 2017 Fundacion Sadosky July 8, 2016 Unfortunate History of Transient Numeric Identifiers draft-gont-numeric-ids-history-00 Abstract This document performs an analysis of the security and privacy implications of different types of "numeric identifiers" used in IETF protocols, and tries to categorize them based on their interoperability requirements and the associated failure severity when such requirements are not met. It describes a number of algorithms that have been employed in real implementations to meet such requirements and analyzes their security and privacy properties. Additionally, it provides advice on possible algorithms that could be employed to satisfy the interoperability requirements of each identifier type, while minimizing the security and privacy implications, thus providing guidance to protocol designers and protocol implementers. Finally, it provides recommendations for future protocol specifications regarding the specification of the aforementioned numeric identifiers. Status of This Memo 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 January 9, 2017. Gont & Arce Expires January 9, 2017 [Page 1] Internet-Draft Predictable Numeric IDs July 2016 Copyright Notice Copyright (c) 2016 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. This document may not be modified, and derivative works of it may not be created, and it may not be published except as an Internet-Draft. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Threat Model . . . . . . . . . . . . . . . . . . . . . . . . 5 4. IPv4/IPv6 Identification . . . . . . . . . . . . . . . . . . 5 5. TCP Initial Sequence Numbers (ISNs) . . . . . . . . . . . . . 6 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 7. Security Considerations . . . . . . . . . . . . . . . . . . . 7 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 9.1. Normative References . . . . . . . . . . . . . . . . . . 7 9.2. Informative References . . . . . . . . . . . . . . . . . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12 1. Introduction Network protocols employ a variety of 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 associated failure severities when such properties are not met, ranging from soft to hard failures. For more than 30 years, a large number of implementations of the TCP/ IP protocol suite have been subject to a variety of attacks, with effects ranging from Denial of Service (DoS) or data injection, to information leakage that could be exploited for pervasive monitoring Gont & Arce Expires January 9, 2017 [Page 2] Internet-Draft Predictable Numeric IDs July 2016 [RFC7528]. The root of these issues has been, in many cases, the poor selection of identifiers in such protocols, usually as a result of an insufficient or misleading specification. While it is generally trivial to identify an algorithm that can satisfy the interoperability requirements for a given identifier, there exists practical evidence 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: o Predictable TCP Initial Sequence Numbers (ISNs) (see e.g. [Morris1985]) o Predictable ephemeral transport protocol numbers (see e.g. [RFC6056] and [Silbersack2005]) o Predictable IPv4 or IPv6 Fragment Identifiers (see e.g. [RFC5722], [RFC6274], and [RFC7739]) o Predictable IPv6 IIDs (see e.g. [RFC7721] and [RFC7707]) o Predictable DNS TxIDs Recent history indicate 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 identifier values are either suggested in the specification or selected by implementers. This document contains a non-exhaustive timeline of vulnerability disclosures related to some sample transient numeric identifiers and other work that has led to advances in this area, with the goal of illustrating that: o Vulnerabilities related to how the values for some identifiers are generated and assigned have affected implementations for an extremely long period of time. o Such vulnerabilities, even when addressed for a given protocol version, were later reintroduced in new versions or new implementations of the same protocol. o Standardization efforts that discuss and provide advice in this area can have a positive effect on protocol specifications and protocol implementations. Gont & Arce Expires January 9, 2017 [Page 3] Internet-Draft Predictable Numeric IDs July 2016 Other related documents (such as [I-D.gont-numeric-ids-sec-considerations]) provide guidance in this area. 2. Terminology 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. Identifiers are usually defined as a series of bits and represented using integer values. We note that different identifiers may have additional requirements or properties depending on their specific use in a protocol. We use the term "identifier" as a generic term to refer to any data object in a protocol specification that satisfies the identification property stated above. Failure Severity: The 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. 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", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. Gont & Arce Expires January 9, 2017 [Page 4] Internet-Draft Predictable Numeric IDs July 2016 3. Threat Model Throughout this document, we assume an attacker does not have physical or logical device to the device(s) being attacked. We assume the attacker can simply send any traffic to the target devices, to e.g. sample identifiers employed by such devices. 4. IPv4/IPv6 Identification December 1998: [Sanfilippo1998a] finds that predictable IPv4 Identification values 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. November 1999: [Sanfilippo1999] discusses how to leverage predictable IPv4 Identification to uncover the rules of a number of firewalls. November 1999: [Bellovin2002] explains how the IPv4 Identification field can be exploited to count the number of systems behind a NAT. December 2003: [Zalewski2003] explains a technique to perform TCP data injection attack based on predictable IPv4 identification values which requires less effort than TCP injection attacks performed with bare TCP packets. November 2005: [Silbersack2005] discusses shortcoming 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 idle scan attacks in IPv6. November 2011: Linux mitigates predictable IPv6 Identification values [RedHat2011] [SUSE2011] [Ubuntu2011]. December 2011: Gont & Arce Expires January 9, 2017 [Page 5] Internet-Draft Predictable Numeric IDs July 2016 [I-D.ietf-6man-predictable-fragment-id-08] describes the security implications of predictable IPv6 Identification values, and possible mitigations. May 2012: [Gont2012] notes that some major IPv6 implementations still employ predictable IPv6 Identification values. June 2015: [I-D.ietf-6man-predictable-fragment-id-08] notes that some popular host and router implementations still employ predictable IPv6 Identification values. 5. TCP Initial Sequence Numbers (ISNs) 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 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 implications of predictable ISNs (along with a range of other protocol-based vulnerabilities). February 1995: [Shimomura1995] reported a real-world exploitation of the attack described in 1985 (ten years before) in [Morris1985]. May 1996: [RFC1948] was the first IETF effort, authored by Steven Bellovin, to address predictable TCP ISNs. 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]. 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: Gont & Arce Expires January 9, 2017 [Page 6] Internet-Draft Predictable Numeric IDs July 2016 Vulnerability advisories [CERT2001] [USCERT2001] are released regarding statistical weaknesses in some ISN generators, affecting popular TCP/IP 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]. February 2012: [RFC6528], after 27 years of 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 algorithm for TCP ISN generation. 6. IANA Considerations There are no IANA registries within this document. The RFC-Editor can remove this section before publication of this document as an RFC. 7. Security Considerations The entire document is about the security and privacy implications of identifiers. 8. Acknowledgements 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. 9. References 9.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <http://www.rfc-editor.org/info/rfc2119>. Gont & Arce Expires January 9, 2017 [Page 7] Internet-Draft Predictable Numeric IDs July 2016 [RFC0793] Postel, J., "Transmission Control Protocol", STD 7, RFC 793, DOI 10.17487/RFC0793, September 1981, <http://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, <http://www.rfc-editor.org/info/rfc6528>. [RFC4086] Eastlake 3rd, D., Schiller, J., and S. Crocker, "Randomness Requirements for Security", BCP 106, RFC 4086, DOI 10.17487/RFC4086, June 2005, <http://www.rfc-editor.org/info/rfc4086>. [RFC5722] Krishnan, S., "Handling of Overlapping IPv6 Fragments", RFC 5722, DOI 10.17487/RFC5722, December 2009, <http://www.rfc-editor.org/info/rfc5722>. [RFC6151] Turner, S. and L. Chen, "Updated Security Considerations for the MD5 Message-Digest and the HMAC-MD5 Algorithms", RFC 6151, DOI 10.17487/RFC6151, March 2011, <http://www.rfc-editor.org/info/rfc6151>. [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, <http://www.rfc-editor.org/info/rfc7217>. 9.2. Informative References [RFC6274] Gont, F., "Security Assessment of the Internet Protocol Version 4", RFC 6274, DOI 10.17487/RFC6274, July 2011, <http://www.rfc-editor.org/info/rfc6274>. [RFC7528] Higgs, P. and J. Piesing, "A Uniform Resource Name (URN) Namespace for the Hybrid Broadcast Broadband TV (HbbTV) Association", RFC 7528, DOI 10.17487/RFC7528, April 2015, <http://www.rfc-editor.org/info/rfc7528>. [RFC1948] Bellovin, S., "Defending Against Sequence Number Attacks", RFC 1948, DOI 10.17487/RFC1948, May 1996, <http://www.rfc-editor.org/info/rfc1948>. Gont & Arce Expires January 9, 2017 [Page 8] Internet-Draft Predictable Numeric IDs July 2016 [CPNI-TCP] Gont, F., "Security Assessment of the Transmission Control Protocol (TCP)", United Kingdom's Centre for the Protection of National Infrastructure (CPNI) Technical Report, 2009, <http://www.gont.com.ar/papers/ tn-03-09-security-assessment-TCP.pdf>. [Zalewski2001] Zalewski, M., "Strange Attractors and TCP/IP Sequence Number Analysis", 2001, <http://lcamtuf.coredump.cx/oldtcp/tcpseq.html>. [Zalewski2002] Zalewski, M., "Strange Attractors and TCP/IP Sequence Number Analysis - One Year Later", 2001, <http://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>. [Joncheray1995] Joncheray, L., "A Simple Active Attack Against TCP", Proc. Fifth Usenix UNIX Security Symposium, 1995. [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, <http://www.kb.cert.org/vuls/id/498440>. [CERT2001] CERT, , "CERT Advisory CA-2001-09: Statistical Weaknesses in TCP/IP Initial Sequence Numbers", 2001, <http://www.cert.org/advisories/CA-2001-09.html>. Gont & Arce Expires January 9, 2017 [Page 9] Internet-Draft Predictable Numeric IDs July 2016 [Shimomura1995] Shimomura, T., "Technical details of the attack described by Markoff in NYT", Message posted in USENET's comp.security.misc newsgroup Message-ID: <firstname.lastname@example.org>, 1995, <http://www.gont.com.ar/docs/post-shimomura-usenet.txt>. [I-D.eddy-rfc793bis-04] Eddy, W., "Transmission Control Protocol Specification", draft-eddy-rfc793bis-04 (work in progress), August 2014. [RFC6056] Larsen, M. and F. Gont, "Recommendations for Transport- Protocol Port Randomization", BCP 156, RFC 6056, DOI 10.17487/RFC6056, January 2011, <http://www.rfc-editor.org/info/rfc6056>. [RFC1035] Mockapetris, P., "Domain names - implementation and specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, November 1987, <http://www.rfc-editor.org/info/rfc1035>. [RFC7739] Gont, F., "Security Implications of Predictable Fragment Identification Values", RFC 7739, DOI 10.17487/RFC7739, February 2016, <http://www.rfc-editor.org/info/rfc7739>. [RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly Errors at High Data Rates", RFC 4963, DOI 10.17487/RFC4963, July 2007, <http://www.rfc-editor.org/info/rfc4963>. [Bellovin2002] Bellovin, S., "A Technique for Counting NATted Hosts", IMW'02 Nov. 6-8, 2002, Marseille, France, 2002. [Fyodor2004] Fyodor, , "Idle scanning and related IP ID games", 2004, <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, <http://www.kyuzz.org/antirez/papers/dumbscan.html>. Gont & Arce Expires January 9, 2017 [Page 10] Internet-Draft Predictable Numeric IDs July 2016 [Sanfilippo1999] Sanfilippo, S., "more ip id", Post to Bugtraq mailing- list, 1999, <http://www.kyuzz.org/antirez/papers/moreipid.html>. [Silbersack2005] Silbersack, M., "Improving TCP/IP security through randomization without sacrificing interoperability", EuroBSDCon 2005 Conference, 2005, <http://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, <http://lcamtuf.coredump.cx/ipfrag.txt>. [Klein2007] Klein, A., "OpenBSD DNS Cache Poisoning and Multiple O/S Predictable IP ID Vulnerability", 2007, <http://www.trusteer.com/files/OpenBSD_DNS_Cache_Poisoning _and_Multiple_OS_Predictable_IP_ID_Vulnerability.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, <http://www.ubuntu.com/usn/usn-1253-1/>. [SUSE2011] SUSE, , "SUSE Security Announcement: Linux kernel security update (SUSE-SA:2011:046)", 2011, <http://lists.opensuse.org/ opensuse-security-announce/2011-12/msg00011.html>. [Gont2012] Gont, F., "Recent Advances in IPv6 Security", BSDCan 2012 Conference Ottawa, Canada. May 11-12, 2012, May 2012. Gont & Arce Expires January 9, 2017 [Page 11] Internet-Draft Predictable Numeric IDs July 2016 [I-D.ietf-6man-predictable-fragment-id-08] Gont, F., "Security Implications of Predictable Fragment Identification Values", draft-ietf-6man-predictable- fragment-id-08 (work in progress), June 2015. [I-D.ietf-6man-default-iids] Gont, F., Cooper, A., Thaler, D., and S. (Will), "Recommendation on Stable IPv6 Interface Identifiers", draft-ietf-6man-default-iids-11 (work in progress), April 2016. [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, <http://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, <http://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", draft-gont-predictable-numeric-ids-00 (work in progress), February 2016. [I-D.gont-numeric-ids-sec-considerations] Gont, F. and I. Arce, "Security Considerations for Transient Numeric Identifiers Employed in Network Protocols", draft-gont-numeric-ids-sec-considerations-00 (work in progress), June 2016. Authors' Addresses Fernando Gont SI6 Networks / UTN-FRH Evaristo Carriego 2644 Haedo, Provincia de Buenos Aires 1706 Argentina Phone: +54 11 4650 8472 Email: email@example.com URI: http://www.si6networks.com Gont & Arce Expires January 9, 2017 [Page 12] Internet-Draft Predictable Numeric IDs July 2016 Ivan Arce Fundacion Dr. Manuel Sadosky Av. Cordoba 744 Piso 5 Oficina I Ciudad Autonoma de Buenos Aires, Buenos Aires C1054AAT Argentina Phone: +54 11 4328 5164 Email: firstname.lastname@example.org URI: http://www.fundacionsadosky.org.ar Gont & Arce Expires January 9, 2017 [Page 13]