[openssl-users] OpenSSL Security Advisory

Tue Mar 1 14:05:39 UTC 2016

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OpenSSL Security Advisory [1st March 2016]
=========================================

NOTE: With this update, OpenSSL is disabling the SSLv2 protocol by default, as
well as removing SSLv2 EXPORT ciphers.  We strongly advise against the use of
SSLv2 due not only to the issues described below, but to the other known
deficiencies in the protocol as described at
https://tools.ietf.org/html/rfc6176

Cross-protocol attack on TLS using SSLv2 (DROWN) (CVE-2016-0800)
================================================================

Severity: High

A cross-protocol attack was discovered that could lead to decryption of TLS
sessions by using a server supporting SSLv2 and EXPORT cipher suites as a
Bleichenbacher RSA padding oracle.  Note that traffic between clients and
non-vulnerable servers can be decrypted provided another server supporting
SSLv2 and EXPORT ciphers (even with a different protocol such as SMTP, IMAP or
POP) shares the RSA keys of the non-vulnerable server. This vulnerability is
known as DROWN (CVE-2016-0800).

Recovering one session key requires the attacker to perform approximately 2^50
computation, as well as thousands of connections to the affected server. A more
efficient variant of the DROWN attack exists against unpatched OpenSSL servers
using versions that predate 1.0.2a, 1.0.1m, 1.0.0r and 0.9.8zf released on
19/Mar/2015 (see CVE-2016-0703 below).

Users can avoid this issue by disabling the SSLv2 protocol in all their SSL/TLS
servers, if they've not done so already. Disabling all SSLv2 ciphers is also
sufficient, provided the patches for CVE-2015-3197 (fixed in OpenSSL 1.0.1r and
1.0.2f) have been deployed.  Servers that have not disabled the SSLv2 protocol,
and are not patched for CVE-2015-3197 are vulnerable to DROWN even if all SSLv2
ciphers are nominally disabled, because malicious clients can force the use of
SSLv2 with EXPORT ciphers.

OpenSSL 1.0.2g and 1.0.1s deploy the following mitigation against DROWN:

SSLv2 is now by default disabled at build-time.  Builds that are not configured
with "enable-ssl2" will not support SSLv2.  Even if "enable-ssl2" is used,
users who want to negotiate SSLv2 via the version-flexible SSLv23_method() will
need to explicitly call either of:

   SSL_CTX_clear_options(ctx, SSL_OP_NO_SSLv2);
   or
   SSL_clear_options(ssl, SSL_OP_NO_SSLv2);

as appropriate.  Even if either of those is used, or the application explicitly
uses the version-specific SSLv2_method() or its client or server variants,
SSLv2 ciphers vulnerable to exhaustive search key recovery have been removed.
Specifically, the SSLv2 40-bit EXPORT ciphers, and SSLv2 56-bit DES are no
longer available.

In addition, weak ciphers in SSLv3 and up are now disabled in default builds of
OpenSSL.  Builds that are not configured with "enable-weak-ssl-ciphers" will
not provide any "EXPORT" or "LOW" strength ciphers.

OpenSSL 1.0.2 users should upgrade to 1.0.2g
OpenSSL 1.0.1 users should upgrade to 1.0.1s

This issue was reported to OpenSSL on December 29th 2015 by Nimrod Aviram and
Sebastian Schinzel. The fix was developed by Viktor Dukhovni and Matt Caswell
of OpenSSL.

Double-free in DSA code (CVE-2016-0705)
=======================================

Severity: Low

A double free bug was discovered when OpenSSL parses malformed DSA private keys
and could lead to a DoS attack or memory corruption for applications that
receive DSA private keys from untrusted sources.  This scenario is considered
rare.

This issue affects OpenSSL versions 1.0.2 and 1.0.1.

OpenSSL 1.0.2 users should upgrade to 1.0.2g
OpenSSL 1.0.1 users should upgrade to 1.0.1s

This issue was reported to OpenSSL on February 7th 2016 by Adam Langley
(Google/BoringSSL) using libFuzzer. The fix was developed by Dr Stephen Henson
of OpenSSL.

Memory leak in SRP database lookups (CVE-2016-0798)
===================================================

Severity: Low

The SRP user database lookup method SRP_VBASE_get_by_user had
confusing memory management semantics; the returned pointer was sometimes newly
allocated, and sometimes owned by the callee. The calling code has no way of
distinguishing these two cases.

Specifically, SRP servers that configure a secret seed to hide valid
login information are vulnerable to a memory leak: an attacker
connecting with an invalid username can cause a memory leak of around
300 bytes per connection.  Servers that do not configure SRP, or
configure SRP but do not configure a seed are not vulnerable.

In Apache, the seed directive is known as SSLSRPUnknownUserSeed.

To mitigate the memory leak, the seed handling in
SRP_VBASE_get_by_user is now disabled even if the user has configured
a seed.  Applications are advised to migrate to
SRP_VBASE_get1_by_user. However, note that OpenSSL makes no strong
guarantees about the indistinguishability of valid and invalid
logins. In particular, computations are currently not carried out in
constant time.

This issue affects OpenSSL versions 1.0.2 and 1.0.1.

OpenSSL 1.0.2 users should upgrade to 1.0.2g
OpenSSL 1.0.1 users should upgrade to 1.0.1s

This issue was discovered on February 23rd 2016 by Emilia KÃ¤sper of
the OpenSSL development team. Emilia KÃ¤sper also developed the fix.

BN_hex2bn/BN_dec2bn NULL pointer deref/heap corruption (CVE-2016-0797)
======================================================================

Severity: Low

All OpenSSL internal usage of these functions use data that is not expected to
be untrusted, e.g. config file data or application command line arguments. If
user developed applications generate config file data based on untrusted data
then it is possible that this could also lead to security consequences. This is
also anticipated to be rare.

This issue affects OpenSSL versions 1.0.2 and 1.0.1.

OpenSSL 1.0.2 users should upgrade to 1.0.2g
OpenSSL 1.0.1 users should upgrade to 1.0.1s

This issue was reported to OpenSSL on February 19th 2016 by Guido Vranken.  The
fix was developed by Matt Caswell of the OpenSSL development team.

Fix memory issues in BIO_*printf functions (CVE-2016-0799)
==========================================================

Severity: Low

The internal |fmtstr| function used in processing a "%s" format string in the
BIO_*printf functions could overflow while calculating the length of a string
and cause an OOB read when printing very long strings.

Additionally the internal |doapr_outch| function can attempt to write to an OOB
memory location (at an offset from the NULL pointer) in the event of a memory
allocation failure. In 1.0.2 and below this could be caused where the size of a
buffer to be allocated is greater than INT_MAX. E.g. this could be in processing
a very long "%s" format string. Memory leaks can also occur.

The first issue may mask the second issue dependent on compiler behaviour.
These problems could enable attacks where large amounts of untrusted data is
passed to the BIO_*printf functions. If applications use these functions in this
way then they could be vulnerable. OpenSSL itself uses these functions when
printing out human-readable dumps of ASN.1 data. Therefore applications that
print this data could be vulnerable if the data is from untrusted sources.
OpenSSL command line applications could also be vulnerable where they print out
ASN.1 data, or if untrusted data is passed as command line arguments.

Libssl is not considered directly vulnerable. Additionally certificates etc
received via remote connections via libssl are also unlikely to be able to
trigger these issues because of message size limits enforced within libssl.

This issue affects OpenSSL versions 1.0.2 and 1.0.1.

OpenSSL 1.0.2 users should upgrade to 1.0.2g
OpenSSL 1.0.1 users should upgrade to 1.0.1s

This issue was reported to OpenSSL on February 23rd by Guido Vranken.  The
fix was developed by Matt Caswell of the OpenSSL development team.

Side channel attack on modular exponentiation (CVE-2016-0702)
=============================================================

Severity: Low

A side-channel attack was found which makes use of cache-bank conflicts on the
Intel Sandy-Bridge microarchitecture which could lead to the recovery of RSA
keys.  The ability to exploit this issue is limited as it relies on an attacker
who has control of code in a thread running on the same hyper-threaded core as
the victim thread which is performing decryptions.

This issue affects OpenSSL versions 1.0.2 and 1.0.1.

OpenSSL 1.0.2 users should upgrade to 1.0.2g
OpenSSL 1.0.1 users should upgrade to 1.0.1s

This issue was reported to OpenSSL on Jan 8th 2016 by Yuval Yarom, The
University of Adelaide and NICTA, Daniel Genkin, Technion and Tel Aviv
University, and Nadia Heninger, University of Pennsylvania with more
information at http://cachebleed.info.  The fix was developed by Andy Polyakov
of OpenSSL.

Divide-and-conquer session key recovery in SSLv2 (CVE-2016-0703)
================================================================

Severity: High

This issue only affected versions of OpenSSL prior to March 19th 2015 at which
time the code was refactored to address vulnerability CVE-2015-0293.

s2_srvr.c did not enforce that clear-key-length is 0 for non-export ciphers. If
clear-key bytes are present for these ciphers, they *displace* encrypted-key
bytes. This leads to an efficient divide-and-conquer key recovery attack: if an
eavesdropper has intercepted an SSLv2 handshake, they can use the server as an
oracle to determine the SSLv2 master-key, using only 16 connections to the
server and negligible computation.

More importantly, this leads to a more efficient version of DROWN that is
effective against non-export ciphersuites, and requires no significant
computation.

This issue affected OpenSSL versions 1.0.2, 1.0.1l, 1.0.0q, 0.9.8ze and all
earlier versions.  It was fixed in OpenSSL 1.0.2a, 1.0.1m, 1.0.0r and 0.9.8zf
(released March 19th 2015).

This issue was reported to OpenSSL on February 10th 2016 by David Adrian and J.
Alex Halderman of the University of Michigan.  The underlying defect had by
then already been fixed by Emilia KÃ¤sper of OpenSSL on March 4th 2015.  The fix
for this issue can be identified by commits ae50d827 (1.0.2a), cd56a08d
(1.0.1m), 1a08063 (1.0.0r) and 65c588c (0.9.8zf).

Bleichenbacher oracle in SSLv2 (CVE-2016-0704)
==============================================

Severity: Moderate

This issue only affected versions of OpenSSL prior to March 19th 2015 at which
time the code was refactored to address the vulnerability CVE-2015-0293.

s2_srvr.c overwrite the wrong bytes in the master-key when applying
Bleichenbacher protection for export cipher suites.  This provides a
Bleichenbacher oracle, and could potentially allow more efficient variants of
the DROWN attack.

This issue affected OpenSSL versions 1.0.2, 1.0.1l, 1.0.0q, 0.9.8ze and all
earlier versions.  It was fixed in OpenSSL 1.0.2a, 1.0.1m, 1.0.0r and 0.9.8zf
(released March 19th 2015).

This issue was reported to OpenSSL on February 10th 2016 by David Adrian and J.
Alex Halderman of the University of Michigan.  The underlying defect had by
then already been fixed by Emilia KÃ¤sper of OpenSSL on March 4th 2015.  The fix
for this issue can be identified by commits ae50d827 (1.0.2a), cd56a08d
(1.0.1m), 1a08063 (1.0.0r) and 65c588c (0.9.8zf).

Note
====

As per our previous announcements and our Release Strategy
(https://www.openssl.org/policies/releasestrat.html), support for OpenSSL
version 1.0.1 will cease on 31st December 2016. No security updates for that
version will be provided after that date. Users of 1.0.1 are advised to
upgrade.

Support for versions 0.9.8 and 1.0.0 ended on 31st December 2015. Those
versions are no longer receiving security updates.

References
==========

URL for this Security Advisory:
https://www.openssl.org/news/secadv/20160301.txt

Note: the online version of the advisory may be updated with additional details
over time.

For details of OpenSSL severity classifications please see:
https://www.openssl.org/policies/secpolicy.html
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