draft-ietf-uta-tls-attacks-04.txt		draft-ietf-uta-tls-attacks-05.txt
	uta Y. Sheffer		uta Y. Sheffer
	Internet-Draft Porticor		Internet-Draft Porticor
	Intended status: Informational R. Holz		Intended status: Informational R. Holz
	Expires: April 1, 2015 TUM		Expires: April 26, 2015 TUM
	P. Saint-Andre		P. Saint-Andre
	&yet		&yet
	September 28, 2014		October 23, 2014
	Summarizing Current Attacks on TLS and DTLS		Summarizing Known Attacks on TLS and DTLS
	draft-ietf-uta-tls-attacks-04		draft-ietf-uta-tls-attacks-05
	Abstract		Abstract
	Over the last few years there have been several serious attacks on		Over the last few years there have been several serious attacks on
	TLS, including attacks on its most commonly used ciphers and modes of		Transport Layer Security (TLS), including attacks on its most
	operation. This document summarizes these attacks, with the goal of		commonly used ciphers and modes of operation. This document
	motivating generic and protocol-specific recommendations on the usage		summarizes these attacks, with the goal of motivating generic and
	of TLS and DTLS.		protocol-specific recommendations on the usage of TLS and Datagram
			TLS (DTLS).
	Status of This Memo		Status of This Memo
	This Internet-Draft is submitted in full conformance with the		This Internet-Draft is submitted in full conformance with the
	provisions of BCP 78 and BCP 79.		provisions of BCP 78 and BCP 79.
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF). Note that other groups may also distribute		Task Force (IETF). Note that other groups may also distribute
	working documents as Internet-Drafts. The list of current Internet-		working documents as Internet-Drafts. The list of current Internet-
	Drafts is at http://datatracker.ietf.org/drafts/current/.		Drafts is at http://datatracker.ietf.org/drafts/current/.
	Internet-Drafts are draft documents valid for a maximum of six months		Internet-Drafts are draft documents valid for a maximum of six months
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
	time. It is inappropriate to use Internet-Drafts as reference		time. It is inappropriate to use Internet-Drafts as reference
	material or to cite them other than as "work in progress."		material or to cite them other than as "work in progress."
	This Internet-Draft will expire on April 1, 2015.		This Internet-Draft will expire on April 26, 2015.
	Copyright Notice		Copyright Notice
	Copyright (c) 2014 IETF Trust and the persons identified as the		Copyright (c) 2014 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
	This document is subject to BCP 78 and the IETF Trust's Legal		This document is subject to BCP 78 and the IETF Trust's Legal
	Provisions Relating to IETF Documents		Provisions Relating to IETF Documents
	(http://trustee.ietf.org/license-info) in effect on the date of		(http://trustee.ietf.org/license-info) in effect on the date of
	publication of this document. Please review these documents		publication of this document. Please review these documents
	skipping to change at page 2, line 15		skipping to change at page 2, line 16
	the Trust Legal Provisions and are provided without warranty as		the Trust Legal Provisions and are provided without warranty as
	described in the Simplified BSD License.		described in the Simplified BSD License.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
	2. Attacks on TLS . . . . . . . . . . . . . . . . . . . . . . . 3		2. Attacks on TLS . . . . . . . . . . . . . . . . . . . . . . . 3
	2.1. SSL Stripping . . . . . . . . . . . . . . . . . . . . . . . 3		2.1. SSL Stripping . . . . . . . . . . . . . . . . . . . . . . . 3
	2.2. STARTTLS Command Injection Attack (CVE-2011-0411) . . . . . 3		2.2. STARTTLS Command Injection Attack (CVE-2011-0411) . . . . . 3
	2.3. BEAST (CVE-2011-3389) . . . . . . . . . . . . . . . . . . . 4		2.3. BEAST (CVE-2011-3389) . . . . . . . . . . . . . . . . . . . 4
	2.4. Lucky Thirteen (CVE-2013-0169) . . . . . . . . . . . . . . 4		2.4. Padding Oracle Attacks . . . . . . . . . . . . . . . . . . 4
	2.5. Attacks on RC4 . . . . . . . . . . . . . . . . . . . . . . 4		2.5. Attacks on RC4 . . . . . . . . . . . . . . . . . . . . . . 4
	2.6. Compression Attacks: CRIME, TIME and BREACH . . . . . . . . 4		2.6. Compression Attacks: CRIME, TIME and BREACH . . . . . . . . 5
	2.7. Certificate Attacks . . . . . . . . . . . . . . . . . . . . 5		2.7. Certificate and RSA-Related Attacks . . . . . . . . . . . . 5
	2.8. Diffie-Hellman Parameters . . . . . . . . . . . . . . . . . 5		2.8. Theft of RSA Private Keys . . . . . . . . . . . . . . . . . 6
	2.9. Renegotiation (CVE-2009-3555) . . . . . . . . . . . . . . . 5		2.9. Diffie-Hellman Parameters . . . . . . . . . . . . . . . . . 6
	2.10. Triple Handshake (CVE-2014-1295) . . . . . . . . . . . . . 5		2.10. Renegotiation (CVE-2009-3555) . . . . . . . . . . . . . . . 6
	2.11. Virtual Host Confusion . . . . . . . . . . . . . . . . . . 6		2.11. Triple Handshake (CVE-2014-1295) . . . . . . . . . . . . . 6
	2.12. Denial of Service . . . . . . . . . . . . . . . . . . . . . 6		2.12. Virtual Host Confusion . . . . . . . . . . . . . . . . . . 7
	2.13. Implementation Issues . . . . . . . . . . . . . . . . . . . 6		2.13. Denial of Service . . . . . . . . . . . . . . . . . . . . . 7
	3. Applicability to DTLS . . . . . . . . . . . . . . . . . . . . 7		2.14. Implementation Issues . . . . . . . . . . . . . . . . . . . 7
	4. Security Considerations . . . . . . . . . . . . . . . . . . . 7		2.15. Usability . . . . . . . . . . . . . . . . . . . . . . . . . 8
	5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7		3. Applicability to DTLS . . . . . . . . . . . . . . . . . . . . 8
	6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7		4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
	7. Informative References . . . . . . . . . . . . . . . . . . . 7		5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
	Appendix A. Appendix: Change Log . . . . . . . . . . . . . . . . 10		6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8
	A.1. draft-ietf-uta-tls-attacks-04 . . . . . . . . . . . . . . . 10		7. Informative References . . . . . . . . . . . . . . . . . . . 9
	A.2. draft-ietf-uta-tls-attacks-03 . . . . . . . . . . . . . . . 10		Appendix A. Appendix: Change Log . . . . . . . . . . . . . . . . 12
	A.3. draft-ietf-uta-tls-attacks-02 . . . . . . . . . . . . . . . 11		A.1. draft-ietf-uta-tls-attacks-05 . . . . . . . . . . . . . . . 13
	A.4. draft-ietf-uta-tls-attacks-01 . . . . . . . . . . . . . . . 11		A.2. draft-ietf-uta-tls-attacks-04 . . . . . . . . . . . . . . . 13
	A.5. draft-ietf-uta-tls-attacks-00 . . . . . . . . . . . . . . . 11		A.3. draft-ietf-uta-tls-attacks-03 . . . . . . . . . . . . . . . 13
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11		A.4. draft-ietf-uta-tls-attacks-02 . . . . . . . . . . . . . . . 13
			A.5. draft-ietf-uta-tls-attacks-01 . . . . . . . . . . . . . . . 13
			A.6. draft-ietf-uta-tls-attacks-00 . . . . . . . . . . . . . . . 13
			Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
	1. Introduction		1. Introduction
	Over the last few years there have been several major attacks on TLS		Over the last few years there have been several major attacks on
	[RFC5246], including attacks on its most commonly used ciphers and		Transport Layer Security (TLS) [RFC5246], including attacks on its
	modes of operation. Details are given in Section 2, but suffice it		most commonly used ciphers and modes of operation. Details are given
	to say that both AES-CBC and RC4, which together make up for most		in Section 2, but a quick summary is that both AES-CBC and RC4, which
	current usage, have been seriously attacked in the context of TLS.		together make up for most current usage, have been seriously attacked
			in the context of TLS.
	This situation was one of the motivations for the creation of the UTA		This situation was one of the motivations for the creation of the UTA
	working group, which is tasked with the creation of generic and		working group, which was tasked with the creation of generic and
	protocol-specific recommendations for the use of TLS and DTLS.		protocol-specific recommendations for the use of TLS along with
			Datagram TLS (DTLS) [RFC6347] (unless otherwise noted under
			Section 3, all of the information provided in this document applies
			to DTLS).
	"Attacks always get better; they never get worse" (ironically, this		"Attacks always get better; they never get worse" (ironically, this
	saying is attributed to the NSA). This list of attacks describes our		saying is attributed to the U.S. National Security Agency, the NSA).
	knowledge as of this writing. It seems likely that new attacks will		This attacks summarized in this document reflect our knowledge as of
	be invented in the future.		this writing. It seems likely that new attacks will be discovered in
			the future.
	For a more detailed discussion of the attacks listed here, the		For a more detailed discussion of the attacks listed here, the
	interested reader is referred to [Attacks-iSec].		interested reader is referred to [Attacks-iSec].
	2. Attacks on TLS		2. Attacks on TLS
	This section lists the attacks that motivated the current		This section lists the attacks that motivated the current
	recommendations. This is not intended to be an extensive survey of		recommendations in [I-D.ietf-uta-tls-bcp]. This list is not intended
	TLS's security.		to be an extensive survey of the security of TLS.
	While there are widely deployed mitigations for some of the attacks		While there are widely deployed mitigations for some of the attacks
	listed below, we believe that their root causes necessitate a more		listed below, we believe that their root causes necessitate a more
	systemic solution.		systematic solution, which we have attempted to develop in
			[I-D.ietf-uta-tls-bcp].
	When such an identifier exists for an attack, we have included its		When an identifier exists for an attack, we have included its CVE
	CVE (Common Vulnerabilities and Exposures) ID. CVE [CVE] is an		(Common Vulnerabilities and Exposures) ID. CVE [CVE] is an
	extensive, industry-wide database of software vulnerabilities.		extensive, industry-wide database of software vulnerabilities.
	2.1. SSL Stripping		2.1. SSL Stripping
	Various attacks attempt to remove the use of SSL/TLS altogether, by		Various attacks attempt to remove the use of SSL/TLS altogether, by
	modifying unencrypted protocols that request the use of TLS,		modifying unencrypted protocols that request the use of TLS,
	specifically modifying HTTP traffic and HTML pages as they pass on		specifically modifying HTTP traffic and HTML pages as they pass on
	the wire. These attacks are known collectively as SSL Stripping and		the wire. These attacks are known collectively as SSL Stripping (a
	were first introduced by Moxie Marlinspike [SSL-Stripping]. In the		form of the more generic "downgrade attack") and were first
	context of Web traffic, these attacks are only effective if the		introduced by Moxie Marlinspike [SSL-Stripping]. In the context of
	client initially accesses a Web server using HTTP. A commonly used		Web traffic, these attacks are only effective if the client initially
	mitigation is HTTP Strict Transport Security (HSTS) [RFC6797].		accesses a Web server using HTTP. A commonly used mitigation is HTTP
			Strict Transport Security (HSTS) [RFC6797].
	2.2. STARTTLS Command Injection Attack (CVE-2011-0411)		2.2. STARTTLS Command Injection Attack (CVE-2011-0411)
	Similarly, there are attacks on the transition between unprotected		Similarly, there are attacks on the transition between unprotected
	and TLS-protected traffic. A number of IETF application protocols		and TLS-protected traffic. A number of IETF application protocols
	have used an application-level command, usually STARTTLS, to upgrade		have used an application-level command, usually STARTTLS, to upgrade
	a clear-text connection to use TLS. Multiple implementations of		a clear-text connection to use TLS. Multiple implementations of
	STARTTLS had a flaw where an application-layer input buffer retained		STARTTLS had a flaw where an application-layer input buffer retained
	commands that were pipelined with the STARTTLS command, such that		commands that were pipelined with the STARTTLS command, such that
	commands received prior to TLS negotiation are executed after TLS		commands received prior to TLS negotiation are executed after TLS
	negotiation. This problem is resolved by requiring the application-		negotiation. This problem is resolved by requiring the application-
	level command input buffer to be empty before negotiating TLS. Note		level command input buffer to be empty before negotiating TLS. Note
	that this flaw lives in the application layer code and does not		that this flaw lives in the application layer code and does not
	impact the TLS protocol directly.		impact the TLS protocol directly.
			STARTLS and similar mechanisms are vulnerable to downgrade attacks
			whereby the attacker simply removes the STARTTLS indication from the
			(unprotected) request. This cannot be mitigated unless HSTS-like
			solutions are added.
	2.3. BEAST (CVE-2011-3389)		2.3. BEAST (CVE-2011-3389)
	The BEAST attack [BEAST] uses issues with the TLS 1.0 implementation		The BEAST attack [BEAST] uses issues with the TLS 1.0 implementation
	of CBC (that is, the predictable initialization vector) to decrypt		of CBC (that is, the predictable initialization vector) to decrypt
	parts of a packet, and specifically to decrypt HTTP cookies when HTTP		parts of a packet, and specifically to decrypt HTTP cookies when HTTP
	is run over TLS.		is run over TLS.
	2.4. Lucky Thirteen (CVE-2013-0169)		2.4. Padding Oracle Attacks
	A consequence of the MAC-then-encrypt design in all current versions		A consequence of the MAC-then-encrypt design in all current versions
	of TLS is the existence of padding oracle attacks [Padding-Oracle].		of TLS is the existence of padding oracle attacks [Padding-Oracle].
	A recent incarnation of these attacks is the Lucky Thirteen attack		A recent incarnation of these attacks is the Lucky Thirteen attack
	[CBC-Attack], a timing side-channel attack that allows the attacker		(CVE-2013-0169) [CBC-Attack], a timing side-channel attack that
	to decrypt arbitrary ciphertext.		allows the attacker to decrypt arbitrary ciphertext.
	The Lucky Thirteen attack can be mitigated by using authenticated		The Lucky Thirteen attack can be mitigated by using authenticated
	encryption like AES-GCM [RFC5288] or encrypt-then-mac		encryption like AES-GCM [RFC5288] or encrypt-then-mac
	[I-D.ietf-tls-encrypt-then-mac] instead of the TLS default of MAC-		[I-D.ietf-tls-encrypt-then-mac] instead of the TLS default of MAC-
	then-encrypt.		then-encrypt.
			An even newer variant of the padding oracle attack, one that does not
			use timing information, is the POODLE attack (CVE-2014-3566) [POODLE]
			on SSL 3.0. This attack has no known mitigation.
	2.5. Attacks on RC4		2.5. Attacks on RC4
	The RC4 algorithm [RC4] has been used with TLS (and previously, SSL)		The RC4 algorithm [RC4] has been used with TLS (and previously, SSL)
	for many years. RC4 has long been known to have a variety of		for many years. RC4 has long been known to have a variety of
	cryptographic weaknesses, e.g. [RC4-Attack-Pau], [RC4-Attack-Man],		cryptographic weaknesses, e.g. [RC4-Attack-Pau], [RC4-Attack-Man],
	[RC4-Attack-FMS]. Recent cryptanalysis results [RC4-Attack-AlF]		[RC4-Attack-FMS]. Recent cryptanalysis results [RC4-Attack-AlF]
	exploit biases in the RC4 keystream to recover repeatedly encrypted		exploit biases in the RC4 keystream to recover repeatedly encrypted
	plaintexts.		plaintexts.
	These recent results are on the verge of becoming practically		These recent results are on the verge of becoming practically
	exploitable; currently they require 2^26 sessions or 13x2^30		exploitable; currently they require 2^26 sessions or 13x2^30
	encryptions. As a result, RC4 can no longer be seen as providing a		encryptions. As a result, RC4 can no longer be seen as providing a
	sufficient level of security for TLS sessions. For further details,		sufficient level of security for TLS sessions. For further details,
	the reader is referred to [I-D.ietf-tls-prohibiting-rc4].		the reader is referred to [I-D.ietf-tls-prohibiting-rc4] and the
			references it cites.
	2.6. Compression Attacks: CRIME, TIME and BREACH		2.6. Compression Attacks: CRIME, TIME and BREACH
	The CRIME attack [CRIME] (CVE-2012-4929) allows an active attacker to		The CRIME attack [CRIME] (CVE-2012-4929) allows an active attacker to
	decrypt ciphertext (specifically, cookies) when TLS is used with TLS		decrypt ciphertext (specifically, cookies) when TLS is used with TLS
	level compression.		level compression.
	The TIME attack [TIME] and the later BREACH attack [BREACH]		The TIME attack [TIME] and the later BREACH attack [BREACH] (CVE-
	(CVE-2013-3587, though the number has not been officially allocated)		2013-3587, though the number has not been officially allocated) both
	both make similar use of HTTP-level compression to decrypt secret		make similar use of HTTP-level compression to decrypt secret data
	data passed in the HTTP response. We note that compression of the		passed in the HTTP response. We note that compression of the HTTP
	HTTP message body is much more prevalent than compression at the TLS		message body is much more prevalent than compression at the TLS
	level.		level.
	The former attack can be mitigated by disabling TLS compression. We		The former attack can be mitigated by disabling TLS compression. We
	are not aware of mitigations at the TLS protocol level to the latter		are not aware of mitigations at the TLS protocol level to the latter
	attack, and so application-level mitigations are needed (see		attack, and so application-level mitigations are needed (see
	[BREACH]). For example, implementations of HTTP that use CSRF tokens		[BREACH]). For example, implementations of HTTP that use CSRF tokens
	will need to randomize them even when the recommendations of		will need to randomize them. Even the best practices and
	[I-D.ietf-uta-tls-bcp] are adopted.		recommendations from [I-D.ietf-uta-tls-bcp] are insufficient to
			thwart this attack.
	2.7. Certificate Attacks		2.7. Certificate and RSA-Related Attacks
	There have been several practical attacks on TLS when used with RSA		There have been several practical attacks on TLS when used with RSA
	certificates (the most common use case). These include		certificates (the most common use case). These include
	[Bleichenbacher98] and [Klima03]. While the Bleichenbacher attack		[Bleichenbacher98] and [Klima03]. While the Bleichenbacher attack
	has been mitigated in TLS 1.0, the Klima attack that relies on a		has been mitigated in TLS 1.0, the Klima attack relies on a version-
	version-check oracle is only mitigated by TLS 1.1.		check oracle is only mitigated by TLS 1.1.
	The use of RSA certificates often involves exploitable timing issues		The use of RSA certificates often involves exploitable timing issues
	[Brumley03] (CVE-2003-0147), unless the implementation takes care to		[Brumley03] (CVE-2003-0147), unless the implementation takes care to
	explicitly eliminate them.		explicitly eliminate them.
	A recent certificate fuzzing tool [Brubaker2014using] uncovered		A recent certificate fuzzing tool [Brubaker2014using] uncovered
	numerous vulnerabilities in different TLS libraries, related to		numerous vulnerabilities in different TLS libraries, related to
	certificate validation.		certificate validation.
	2.8. Diffie-Hellman Parameters		2.8. Theft of RSA Private Keys
			When TLS is used with most non-Diffie Hellman cipher suites, it is
			sufficient to obtain the server's private key in order to decrypt any
			sessions (past and future) that were initiated with that server.
			This technique is used, for example, by the popular Wireshark network
			sniffer to inspect TLS-protected connections.
			It is known that stolen (or otherwise obtained) private keys have
			been used as part of large-scale monitoring [RFC7258] of certain
			servers.
			Such attacks can be mitigated by better protecting the private key,
			e.g. using OS protections or dedicated hardware. Even more effective
			is the use of cipher suites that offer "forward secrecy", the
			property that revealing a secret such as a private key does not
			expose past or future sessions to a passive attacker.
			2.9. Diffie-Hellman Parameters
	TLS allows the definition of ephemeral Diffie-Hellman and Elliptic		TLS allows the definition of ephemeral Diffie-Hellman and Elliptic
	Curve Diffie-Hellman parameters in its respective key exchange modes.		Curve Diffie-Hellman parameters in its respective key exchange modes.
	This results in an attack detailed in [Cross-Protocol]. In addition,		This results in an attack detailed in [Cross-Protocol]. Using
	clients that do not properly verify the received parameters are		predefined DH groups, as proposed in
	exposed to man in the middle (MITM) attacks. Unfortunately the TLS		[I-D.ietf-tls-negotiated-ff-dhe], would mitigate this attack.
	protocol does not require this verification, see [RFC6989] for the
	IPsec analogy.
	2.9. Renegotiation (CVE-2009-3555)		In addition, clients that do not properly verify the received
			parameters are exposed to man in the middle (MITM) attacks.
			Unfortunately the TLS protocol does not mandate this verification
			(see [RFC6989] for analogous information for IPsec).
			2.10. Renegotiation (CVE-2009-3555)
	A major attack on the TLS renegotiation mechanism applies to all		A major attack on the TLS renegotiation mechanism applies to all
	current versions of the protocol. The attack and the TLS extension		current versions of the protocol. The attack and the TLS extension
	that resolves it are described in [RFC5746].		that resolves it are described in [RFC5746].
	2.10. Triple Handshake (CVE-2014-1295)		2.11. Triple Handshake (CVE-2014-1295)
	The triple handshake attack [[TRIPLE-HS, add the reference when		The triple handshake attack [BhargavanDFPS14] enables the attacker to
	published]] enables the attacker to cause two TLS connections to		cause two TLS connections to share keying material. This leads to a
	share keying material. This leads to a multitude of attacks, e.g.		multitude of attacks, e.g. Man-in-the-Middle, breaking safe
	Man-in-the-Middle, breaking safe renegotiation and breaking channel		renegotiation, and breaking channel binding via TLS Exporter
	binding via TLS Exporter [RFC5705] or "tls-unique" [RFC5929].		[RFC5705] or "tls-unique" [RFC5929].
	2.11. Virtual Host Confusion		2.12. Virtual Host Confusion
	A recent article [Delignat14] describes a security issue whereby		A recent article [Delignat14] describes a security issue whereby
	SSLv3 fallback and improper handling of session caches on the server		SSLv3 fallback and improper handling of session caches on the server
	side can be abused by an attacker to establish a malicious connection		side can be abused by an attacker to establish a malicious connection
	to a virtual host other than originally intended and approved by the		to a virtual host other than the one originally intended and approved
	server. This attack is especially serious in performance critical		by the server. This attack is especially serious in performance
	environments where sharing of SSLv3 session caches is very common.		critical environments where sharing of SSLv3 session caches is very
			common.
	2.12. Denial of Service		2.13. Denial of Service
	Server CPU power has progressed over the years so that TLS can now be		Server CPU power has progressed over the years so that TLS can now be
	turned on by default. However the risk of malicious clients and		turned on by default. However, the risk of malicious clients and
	coordinated groups of clients ("botnets") mounting denial of service		coordinated groups of clients ("botnets") mounting denial of service
	attacks is still very real. TLS adds another vector for		attacks is still very real. TLS adds another vector for
	computational attacks, since a client can easily (with little		computational attacks, since a client can easily (with little
	computational effort) force the server to expend relatively large		computational effort) force the server to expend relatively large
	computational work. It is known that such attacks have in fact been		computational work. It is known that such attacks have in fact been
	mounted.		mounted.
	2.13. Implementation Issues		2.14. Implementation Issues
	Even when the protocol is fully specified, there are very common		Even when the protocol is properly specified, this does not guarantee
	issues that often plague implementations. In particular, when		the security of implementations. In fact there are very common
			issues that often plague TLS implementations. In particular, when
	integrating into higher-level protocols, TLS and its PKI-based		integrating into higher-level protocols, TLS and its PKI-based
	authentication are sometimes the source of misunderstandings and		authentication are sometimes the source of misunderstandings and
	implementation "shortcuts". An extensive survey of these issues can		implementation "shortcuts". An extensive survey of these issues can
	be found in [Georgiev2012].		be found in [Georgiev2012].
	o Implementations may omit validation of the server certificate		o Implementations might omit validation of the server certificate
	altogether. For example, this is true of the default		altogether. For example, this is true of the default
	implementation of HTTP client libraries in Python 2 (see e.g.		implementation of HTTP client libraries in Python 2 (see e.g.
	CVE-2013-2191).		CVE-2013-2191).
	o Implementations may not validate the server identity. This		o Implementations might not validate the server identity. This
	validation typically amounts to matching the protocol-level server		validation typically amounts to matching the protocol-level server
	name with the certificate's Subject Alternative Name field. Note:		name with the certificate's Subject Alternative Name field. Note:
	historically, although incorrect, this information is also often		this same information is often also found in the Common Name part
	found in the Common Name part of the Distinguished Name instead.		of the Distinguished Name, and some validators incorrectly
			retrieve it from there instead of from the Subject Alternative
			Name.
	o Implementations may be validating the certificate chain		o Implementations might validate the certificate chain incorrectly
	incorrectly or not at all, or using an incorrect or outdated trust		or not at all, or use an incorrect or outdated trust anchor list.
	anchor list.
			An implementation attack of a different kind, one that exploits a
			simple coding mistake (bounds check), is the Heartbleed attack (CVE-
			2014-0160) that affected a wide swath of the Internet when it was
			discovered in April 2014.
			2.15. Usability
			Many TLS endpoints, such as browsers and mail clients, allow the user
			to explicitly accept an invalid server certificate. This often takes
			the form of a UI dialog (e.g., "do you accept this server?") and
			users have been conditioned to respond in the affirmative in order to
			allow the connection to take place.
			This user behavior is used by (arguably legitimate) "SSL proxies"
			that decrypt and re-encrypt the TLS connection in order to enforce
			local security policy. It is also abused by attackers whose goal is
			to gain access to the encrypted information.
			Mitigation is complex and will probably involve a combination of
			protocol mechanisms (HSTS, certificate pinning
			[I-D.ietf-websec-key-pinning]) and very careful UI design.
	3. Applicability to DTLS		3. Applicability to DTLS
	DTLS [RFC4347] [RFC6347] is an adaptation of TLS for UDP datagrams.		DTLS [RFC4347] [RFC6347] is an adaptation of TLS for UDP.
	With respect to the attacks described in the current document, DTLS		With respect to the attacks described in the current document, DTLS
	1.0 is equivalent to TLS 1.1. The only exception is RC4 which is		1.0 is equivalent to TLS 1.1. The only exception is RC4, which is
	disallowed in DTLS. DTLS 1.2 is equivalent to TLS 1.2.		disallowed in DTLS. DTLS 1.2 is equivalent to TLS 1.2.
	4. Security Considerations		4. IANA Considerations
	This document describes protocol attacks in an informational manner,
	and in itself does not have any security implications. Its companion
	documents certainly do.
	5. IANA Considerations
	This document requires no IANA actions. [Note to RFC Editor: please		This document requires no IANA actions. [Note to RFC Editor: please
	remove this whole section before publication.]		remove this whole section before publication.]
			5. Security Considerations
			This document describes protocol attacks in an informational manner,
			and in itself does not have any security implications. Its companion
			documents, especially [I-D.ietf-uta-tls-bcp], certainly do.
	6. Acknowledgments		6. Acknowledgments
	We would like to thank Stephen Farrell, Simon Josefsson, John		We would like to thank Stephen Farrell, Simon Josefsson, John
	Mattsson, Yoav Nir, Kenny Paterson, Patrick Pelletier, Tom Ritter and		Mattsson, Yoav Nir, Kenny Paterson, Patrick Pelletier, Tom Ritter,
	Rich Salz for their review of this document. We thank Andrei Popov		Rich Salz and Meral Shirazipour for their feedback on this document.
	for contributing text on RC4, Kohei Kasamatsu for text on Lucky13,		We thank Andrei Popov for contributing text on RC4, Kohei Kasamatsu
	Ilari Liusvaara for text on attacks and on DTLS, Aaron Zauner for		for text on Lucky13, Ilari Liusvaara for text on attacks and on DTLS,
	text on virtual host confusion, Chris Newman for text on STARTTLS		Aaron Zauner for text on virtual host confusion, and Chris Newman for
	command injection.		text on STARTTLS command injection.
			During IESG review, Richard Barnes, Barry Leiba, and Kathleen
			Moriarty caught several issues that needed to be addressed.
			The authors gratefully acknowledge the assistance of Leif Johansson
			and Orit Levin as the working group chairs and Pete Resnick as the
			sponsoring Area Director.
	The document was prepared using the lyx2rfc tool, created by Nico		The document was prepared using the lyx2rfc tool, created by Nico
	Williams.		Williams.
	7. Informative References		7. Informative References
	[RFC4347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer		[RFC4347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
	Security", RFC 4347, April 2006.		Security", RFC 4347, April 2006.
	[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security		[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
	skipping to change at page 8, line 22		skipping to change at page 9, line 49
	[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer		[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
	Security Version 1.2", RFC 6347, January 2012.		Security Version 1.2", RFC 6347, January 2012.
	[RFC6797] Hodges, J., Jackson, C., and A. Barth, "HTTP Strict		[RFC6797] Hodges, J., Jackson, C., and A. Barth, "HTTP Strict
	Transport Security (HSTS)", RFC 6797, November 2012.		Transport Security (HSTS)", RFC 6797, November 2012.
	[RFC6989] Sheffer, Y. and S. Fluhrer, "Additional Diffie-Hellman		[RFC6989] Sheffer, Y. and S. Fluhrer, "Additional Diffie-Hellman
	Tests for the Internet Key Exchange Protocol Version 2		Tests for the Internet Key Exchange Protocol Version 2
	(IKEv2)", RFC 6989, July 2013.		(IKEv2)", RFC 6989, July 2013.
			[RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an
			Attack", BCP 188, RFC 7258, May 2014.
	[I-D.ietf-uta-tls-bcp]		[I-D.ietf-uta-tls-bcp]
	Sheffer, Y., Holz, R., and P. Saint-Andre,		Sheffer, Y., Holz, R., and P. Saint-Andre,
	"Recommendations for Secure Use of TLS and DTLS", draft-		"Recommendations for Secure Use of TLS and DTLS", draft-
	ietf-uta-tls-bcp-01 (work in progress), June 2014.		ietf-uta-tls-bcp-05 (work in progress), October 2014.
	[I-D.ietf-tls-prohibiting-rc4]		[I-D.ietf-tls-prohibiting-rc4]
	Popov, A., "Prohibiting RC4 Cipher Suites", draft-ietf-		Popov, A., "Prohibiting RC4 Cipher Suites", draft-ietf-
	tls-prohibiting-rc4-00 (work in progress), July 2014.		tls-prohibiting-rc4-00 (work in progress), July 2014.
	[I-D.ietf-tls-encrypt-then-mac]		[I-D.ietf-tls-encrypt-then-mac]
	Gutmann, P., "Encrypt-then-MAC for TLS and DTLS", draft-		Gutmann, P., "Encrypt-then-MAC for TLS and DTLS", draft-
	ietf-tls-encrypt-then-mac-03 (work in progress), July		ietf-tls-encrypt-then-mac-03 (work in progress), July
	2014.		2014.
			[I-D.ietf-tls-negotiated-ff-dhe]
			Gillmor, D., "Negotiated Finite Field Diffie-Hellman
			Ephemeral Parameters for TLS", draft-ietf-tls-negotiated-
			ff-dhe-02 (work in progress), October 2014.
			[I-D.ietf-websec-key-pinning]
			Evans, C., Palmer, C., and R. Sleevi, "Public Key Pinning
			Extension for HTTP", draft-ietf-websec-key-pinning-21
			(work in progress), October 2014.
	[CVE] MITRE, , "Common Vulnerabilities and Exposures",		[CVE] MITRE, , "Common Vulnerabilities and Exposures",
	<https://cve.mitre.org/>.		<https://cve.mitre.org/>.
	[CBC-Attack]		[CBC-Attack]
	AlFardan, N. and K. Paterson, "Lucky Thirteen: Breaking		AlFardan, N. and K. Paterson, "Lucky Thirteen: Breaking
	the TLS and DTLS Record Protocols", IEEE Symposium on		the TLS and DTLS Record Protocols", IEEE Symposium on
	Security and Privacy , 2013.		Security and Privacy , 2013.
	[BEAST] Rizzo, J. and T. Duong, "Browser Exploit Against SSL/TLS",		[BEAST] Rizzo, J. and T. Duong, "Browser Exploit Against SSL/TLS",
	2011, <http://packetstormsecurity.com/files/105499/		2011, <http://packetstormsecurity.com/files/105499/
	Browser-Exploit-Against-SSL-TLS.html>.		Browser-Exploit-Against-SSL-TLS.html>.
			[POODLE] Moeller, B., Duong, T., and K. Kotowicz, "This POODLE
			Bites:Exploiting the SSL 3.0 Fallback", 2014,
			<https://www.openssl.org/~bodo/ssl-poodle.pdf>.
	[CRIME] Rizzo, J. and T. Duong, "The CRIME Attack", EKOparty		[CRIME] Rizzo, J. and T. Duong, "The CRIME Attack", EKOparty
	Security Conference 2012, 2012.		Security Conference 2012, 2012.
	[BREACH] Prado, A., Harris, N., and Y. Gluck, "The BREACH Attack",		[BREACH] Prado, A., Harris, N., and Y. Gluck, "The BREACH Attack",
	2013, <http://breachattack.com/>.		2013, <http://breachattack.com/>.
	[TIME] Be'ery, T. and A. Shulman, "A Perfect CRIME? Only TIME		[TIME] Be'ery, T. and A. Shulman, "A Perfect CRIME? Only TIME
	Will Tell", Black Hat Europe 2013, 2013,		Will Tell", Black Hat Europe 2013, 2013,
	<https://media.blackhat.com/eu-13/briefings/Beery/bh-		<https://media.blackhat.com/eu-13/briefings/Beery/bh-eu-
	eu-13-a-perfect-crime-beery-wp.pdf>.		13-a-perfect-crime-beery-wp.pdf>.
	[RC4] Schneier, B., "Applied Cryptography: Protocols,		[RC4] Schneier, B., "Applied Cryptography: Protocols,
	Algorithms, and Source Code in C, 2nd Ed.", 1996.		Algorithms, and Source Code in C, 2nd Ed.", 1996.
	[RC4-Attack-FMS]		[RC4-Attack-FMS]
	Fluhrer, S., Mantin, I., and A. Shamir, "Weaknesses in the		Fluhrer, S., Mantin, I., and A. Shamir, "Weaknesses in the
	Key Scheduling Algorithm of RC4", Selected Areas in		Key Scheduling Algorithm of RC4", Selected Areas in
	Cryptography , 2001.		Cryptography , 2001.
	[RC4-Attack-AlF]		[RC4-Attack-AlF]
	AlFardan, N., Bernstein, D., Paterson, K., Poettering, B.,		AlFardan, N., Bernstein, D., Paterson, K., Poettering, B.,
	and J. Schuldt, "On the Security of RC4 in TLS", Usenix		and J. Schuldt, "On the Security of RC4 in TLS", Usenix
	Security Symposium 2013, 2013, <https://www.usenix.org/		Security Symposium 2013, 2013,
	conference/usenixsecurity13/security-rc4-tls>.		<https://www.usenix.org/conference/usenixsecurity13/
			security-rc4-tls>.
	[Georgiev2012]		[Georgiev2012]
	Georgiev, M., Iyengar, S., Jana, S., Anubhai, R., Boneh,		Georgiev, M., Iyengar, S., Jana, S., Anubhai, R., Boneh,
	D., and V. Shmatikov, "The most dangerous code in the		D., and V. Shmatikov, "The most dangerous code in the
	world: validating SSL certificates in non-browser		world: validating SSL certificates in non-browser
	software", 2012,		software", 2012,
	<http://doi.acm.org/10.1145/2382196.2382204>.		<http://doi.acm.org/10.1145/2382196.2382204>.
	[Attacks-iSec]		[Attacks-iSec]
	Sarkar, P. and S. Fitzgerald, "Attacks on SSL, a		Sarkar, P. and S. Fitzgerald, "Attacks on SSL, a
	comprehensive study of BEAST, CRIME, TIME, BREACH, Lucky13		comprehensive study of BEAST, CRIME, TIME, BREACH, Lucky13
	and RC4 biases", 8 2013, <https://www.isecpartners.com/		and RC4 biases", 8 2013,
	media/106031/ssl_attacks_survey.pdf>.		<https://www.isecpartners.com/media/106031/
			ssl_attacks_survey.pdf>.
	[Padding-Oracle]		[Padding-Oracle]
	Vaudenay, S., "Security Flaws Induced by CBC Padding		Vaudenay, S., "Security Flaws Induced by CBC Padding
	Applications to SSL, IPSEC, WTLS...", EUROCRYPT 2002,		Applications to SSL, IPSEC, WTLS...", EUROCRYPT 2002,
	2002, <http://www.iacr.org/cryptodb/archive/2002/		2002, <http://www.iacr.org/cryptodb/archive/2002/
	EUROCRYPT/2850/2850.pdf>.		EUROCRYPT/2850/2850.pdf>.
	[Cross-Protocol]		[Cross-Protocol]
	Mavrogiannopoulos, N., Vercauteren, F., Velichkov, V., and		Mavrogiannopoulos, N., Vercauteren, F., Velichkov, V., and
	B. Preneel, "A cross-protocol attack on the TLS protocol",		B. Preneel, "A cross-protocol attack on the TLS protocol",
	skipping to change at page 10, line 35		skipping to change at page 12, line 41
	[Brubaker2014using]		[Brubaker2014using]
	Brubaker, C., Jana, S., Ray, B., Khurshid, S., and V.		Brubaker, C., Jana, S., Ray, B., Khurshid, S., and V.
	Shmatikov, "Using frankencerts for automated adversarial		Shmatikov, "Using frankencerts for automated adversarial
	testing of certificate validation in SSL/TLS		testing of certificate validation in SSL/TLS
	implementations", 2014.		implementations", 2014.
	[Delignat14]		[Delignat14]
	Delignat-Lavaud, A. and K. Bhargavan, "Virtual Host		Delignat-Lavaud, A. and K. Bhargavan, "Virtual Host
	Confusion: Weaknesses and Exploits", Black Hat 2014, 2014.		Confusion: Weaknesses and Exploits", Black Hat 2014, 2014.
			[BhargavanDFPS14]
			Bhargavan, K., Delignat-Lavaud, A., Fournet, C., Pironti,
			A., and P. Strub, "Triple handshakes and cookie cutters:
			breaking and fixing authentication over tls", 2014,
			<http://prosecco.gforge.inria.fr/pubs/
			triple-handshakes-and-cookie-cutters-sp14.pdf>.
	Appendix A. Appendix: Change Log		Appendix A. Appendix: Change Log
	Note to RFC Editor: please remove this section before publication.		Note to RFC Editor: please remove this section before publication.
	A.1. draft-ietf-uta-tls-attacks-04		A.1. draft-ietf-uta-tls-attacks-05
			o Implemented Gen-ART and IESG reviews.
			A.2. draft-ietf-uta-tls-attacks-04
	o Implemented AD review comments.		o Implemented AD review comments.
	A.2. draft-ietf-uta-tls-attacks-03		A.3. draft-ietf-uta-tls-attacks-03
	o Implemented WG Last Call comments.		o Implemented WG Last Call comments.
	o Virtual host confusion.		o Virtual host confusion.
	o STARTTLS command injection.		o STARTTLS command injection.
	o Added CVE numbers.		o Added CVE numbers.
	A.3. draft-ietf-uta-tls-attacks-02		A.4. draft-ietf-uta-tls-attacks-02
	o Added implementation issues ("most dangerous code"),		o Added implementation issues ("most dangerous code"),
	renegotiation, triple handshake.		renegotiation, triple handshake.
	o Added text re: mitigation of Lucky13.		o Added text re: mitigation of Lucky13.
	o Added applicability to DTLS.		o Added applicability to DTLS.
	A.4. draft-ietf-uta-tls-attacks-01		A.5. draft-ietf-uta-tls-attacks-01
	o Added SSL Stripping, attacks related to certificates, Diffie		o Added SSL Stripping, attacks related to certificates, Diffie
	Hellman parameters and denial of service.		Hellman parameters and denial of service.
	o Expanded on RC4 attacks, thanks to Andrei Popov.		o Expanded on RC4 attacks, thanks to Andrei Popov.
	A.5. draft-ietf-uta-tls-attacks-00		A.6. draft-ietf-uta-tls-attacks-00
	o Initial version, extracted from draft-sheffer-tls-bcp-01.		o Initial version, extracted from draft-sheffer-tls-bcp-01.
	Authors' Addresses		Authors' Addresses
	Yaron Sheffer		Yaron Sheffer
	Porticor		Porticor
	29 HaHarash St.		29 HaHarash St.
	Hod HaSharon 4501303		Hod HaSharon 4501303
	Israel		Israel
	skipping to change at page 11, line 45		skipping to change at page 14, line 14
	Ralph Holz		Ralph Holz
	Technische Universitaet Muenchen		Technische Universitaet Muenchen
	Boltzmannstr. 3		Boltzmannstr. 3
	Garching 85748		Garching 85748
	Germany		Germany
	Email: holz@net.in.tum.de		Email: holz@net.in.tum.de
	Peter Saint-Andre		Peter Saint-Andre
	&yet		&yet
	P.O. Box 787
	Parker, CO 80134
	USA
	Email: peter@andyet.com		Email: peter@andyet.com
			URI: https://andyet.com/
End of changes. 58 change blocks.
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