draft-ietf-uta-tls-attacks-03.txt   draft-ietf-uta-tls-attacks-04.txt 
uta Y. Sheffer uta Y. Sheffer
Internet-Draft Porticor Internet-Draft Porticor
Intended status: Informational R. Holz Intended status: Informational R. Holz
Expires: March 13, 2015 TUM Expires: April 1, 2015 TUM
P. Saint-Andre P. Saint-Andre
&yet &yet
September 9, 2014 September 28, 2014
Summarizing Current Attacks on TLS and DTLS Summarizing Current Attacks on TLS and DTLS
draft-ietf-uta-tls-attacks-03 draft-ietf-uta-tls-attacks-04
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 TLS, including attacks on its most commonly used ciphers and modes of
operation. This document summarizes these attacks, with the goal of operation. This document summarizes these attacks, with the goal of
motivating generic and protocol-specific recommendations on the usage motivating generic and protocol-specific recommendations on the usage
of TLS and DTLS. of TLS and DTLS.
Status of This Memo Status of This Memo
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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 March 13, 2015. This Internet-Draft will expire on April 1, 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
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include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
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) . . . . . . . . . . . . . . . . . . . 3 2.3. BEAST (CVE-2011-3389) . . . . . . . . . . . . . . . . . . . 4
2.4. Lucky Thirteen (CVE-2013-0169) . . . . . . . . . . . . . . 4 2.4. Lucky Thirteen (CVE-2013-0169) . . . . . . . . . . . . . . 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 . . . . . . . . 4
2.7. Certificate Attacks . . . . . . . . . . . . . . . . . . . . 5 2.7. Certificate Attacks . . . . . . . . . . . . . . . . . . . . 5
2.8. Diffie-Hellman Parameters . . . . . . . . . . . . . . . . . 5 2.8. Diffie-Hellman Parameters . . . . . . . . . . . . . . . . . 5
2.9. Renegotiation (CVE-2009-3555) . . . . . . . . . . . . . . . 5 2.9. Renegotiation (CVE-2009-3555) . . . . . . . . . . . . . . . 5
2.10. Triple Handshake (CVE-2014-1295) . . . . . . . . . . . . . 5 2.10. Triple Handshake (CVE-2014-1295) . . . . . . . . . . . . . 5
2.11. Virtual Host Confusion . . . . . . . . . . . . . . . . . . 5 2.11. Virtual Host Confusion . . . . . . . . . . . . . . . . . . 6
2.12. Denial of Service . . . . . . . . . . . . . . . . . . . . . 6 2.12. Denial of Service . . . . . . . . . . . . . . . . . . . . . 6
2.13. Implementation Issues . . . . . . . . . . . . . . . . . . . 6 2.13. Implementation Issues . . . . . . . . . . . . . . . . . . . 6
3. Applicability to DTLS . . . . . . . . . . . . . . . . . . . . 6 3. Applicability to DTLS . . . . . . . . . . . . . . . . . . . . 7
4. Security Considerations . . . . . . . . . . . . . . . . . . . 6 4. Security Considerations . . . . . . . . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7
7. Informative References . . . . . . . . . . . . . . . . . . . 7 7. Informative References . . . . . . . . . . . . . . . . . . . 7
Appendix A. Appendix: Change Log . . . . . . . . . . . . . . . . 10 Appendix A. Appendix: Change Log . . . . . . . . . . . . . . . . 10
A.1. draft-ietf-uta-tls-attacks-03 . . . . . . . . . . . . . . . 10 A.1. draft-ietf-uta-tls-attacks-04 . . . . . . . . . . . . . . . 10
A.2. draft-ietf-uta-tls-attacks-02 . . . . . . . . . . . . . . . 10 A.2. draft-ietf-uta-tls-attacks-03 . . . . . . . . . . . . . . . 10
A.3. draft-ietf-uta-tls-attacks-01 . . . . . . . . . . . . . . . 10 A.3. draft-ietf-uta-tls-attacks-02 . . . . . . . . . . . . . . . 11
A.4. draft-ietf-uta-tls-attacks-00 . . . . . . . . . . . . . . . 11 A.4. draft-ietf-uta-tls-attacks-01 . . . . . . . . . . . . . . . 11
A.5. draft-ietf-uta-tls-attacks-00 . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
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 TLS
[RFC5246], including attacks on its most commonly used ciphers and [RFC5246], including attacks on its most commonly used ciphers and
modes of operation. Details are given in Section 2, but suffice it modes of operation. Details are given in Section 2, but suffice it
to say that both AES-CBC and RC4, which together make up for most to say that both AES-CBC and RC4, which together make up for most
current usage, have been seriously attacked in the context of TLS. current usage, have been seriously attacked in the context of TLS.
This situation motivated the creation of the UTA working group, which This situation was one of the motivations for the creation of the UTA
is tasked with the creation of generic and protocol-specific working group, which is tasked with the creation of generic and
recommendations for the use of TLS and DTLS. protocol-specific recommendations for the use of TLS and 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 NSA). This list of attacks describes our
knowledge as of this writing. It seems likely that new attacks will knowledge as of this writing. It seems likely that new attacks will
be invented in the future. be invented 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. This is not intended to be an extensive survey of
TLS's security. TLS's security.
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. systemic solution.
When such an identifier exists for an attack, we have included its
CVE (Common Vulnerabilities and Exposures) ID. CVE [CVE] is an
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 and
were first introduced by Moxie Marlinspike [SSL-Stripping]. In the were first introduced by Moxie Marlinspike [SSL-Stripping]. In the
context of Web traffic, these attacks are only effective if the context of Web traffic, these attacks are only effective if the
client initially accesses a Web server using HTTP. A commonly used client initially accesses a Web server using HTTP. A commonly used
mitigation is HTTP Strict Transport Security (HSTS) [RFC6797]. mitigation is HTTP Strict Transport Security (HSTS) [RFC6797].
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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. Diffie-Hellman Parameters
TLS allows to define ephemeral Diffie-Hellman and Elliptic Curve TLS allows the definition of ephemeral Diffie-Hellman and Elliptic
Diffie-Hellman parameters in its respective key exchange modes. This Curve Diffie-Hellman parameters in its respective key exchange modes.
results in an attack detailed in [Cross-Protocol]. In addition, This results in an attack detailed in [Cross-Protocol]. In addition,
clients that do not properly verify the received parameters are clients that do not properly verify the received parameters are
exposed to man in the middle (MITM) attacks. Unfortunately the TLS exposed to man in the middle (MITM) attacks. Unfortunately the TLS
protocol does not require this verification, see [RFC6989] for the protocol does not require this verification, see [RFC6989] for the
IPsec analogy. IPsec analogy.
2.9. Renegotiation (CVE-2009-3555) 2.9. 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].
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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 2.13. Implementation Issues
Even when the protocol is fully specified, the are very common issues Even when the protocol is fully specified, there are very common
that often plague implementations. In particular, the integration of issues that often plague implementations. In particular, when
higher-level protocols, TLS and its PKI-based authentication is the integrating into higher-level protocols, TLS and its PKI-based
source of misunderstandings and implementation "shortcuts". An authentication are sometimes the source of misunderstandings and
extensive survey of these issues can be found in [Georgiev2012]. implementation "shortcuts". An extensive survey of these issues can
be found in [Georgiev2012].
o Implementations may omit validation of the server certificate o Implementations may 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 may 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 historically, although incorrect, this information is also often
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[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.
[CVE] MITRE, , "Common Vulnerabilities and Exposures",
<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>.
[CRIME] Rizzo, J. and T. Duong, "The CRIME Attack", EKOparty [CRIME] Rizzo, J. and T. Duong, "The CRIME Attack", EKOparty
skipping to change at page 10, line 26 skipping to change at page 10, line 39
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.
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-03 A.1. draft-ietf-uta-tls-attacks-04
o Implemented AD review comments.
A.2. 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.2. draft-ietf-uta-tls-attacks-02 A.3. 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.3. draft-ietf-uta-tls-attacks-01 A.4. 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.4. draft-ietf-uta-tls-attacks-00 A.5. 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
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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: ietf@stpeter.im Email: peter@andyet.com
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