-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA512 ============================================================================= FreeBSD-SA-13:14.openssh Security Advisory The FreeBSD Project Topic: OpenSSH AES-GCM memory corruption vulnerability Category: contrib Module: openssh Announced: 2013-11-19 Revised: 2013-11-28 Affects: FreeBSD 10.0-BETA Corrected: 2013-11-19 09:35:20 UTC (stable/10, 10.0-STABLE) 2013-11-19 09:35:20 UTC (stable/10, 10.0-BETA3-p1) 2013-11-19 09:35:20 UTC (stable/10, 10.0-BETA2-p1) 2013-11-19 09:35:20 UTC (stable/10, 10.0-BETA1-p2) CVE Name: CVE-2013-4548 For general information regarding FreeBSD Security Advisories, including descriptions of the fields above, security branches, and the following sections, please visit . 0. Revision History v1.0 2013-11-19 Initial release. v1.1 2013-11-28 Corrected path to sshd_config. I. Background OpenSSH is an implementation of the SSH protocol suite, providing an encrypted and authenticated transport for a variety of services, including remote shell access. AES-GCM (Galois/Counter Mode) is a mode of operation for AES block cipher that combines the counter mode of encryption with the Galois mode of authentication which can offer throughput rates for state of the art, high speed communication channels. OpenSSH supports the AES-GCM algorithm as specified in RFC 5647. II. Problem Description A memory corruption vulnerability exists in the post-authentication sshd process when an AES-GCM cipher (aes128-gcm@openssh.com or aes256-gcm@openssh.com) is selected during key exchange. III. Impact If exploited, this vulnerability might permit code execution with the privileges of the authenticated user, thereby allowing a malicious user with valid credentials to bypass shell or command restrictions placed on their account. IV. Workaround Disable AES-GCM in the server configuration. This can be accomplished by adding the following /etc/ssh/sshd_config option, which will disable AES-GCM while leaving other ciphers active: Ciphers aes128-ctr,aes192-ctr,aes256-ctr,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc Systems not running the OpenSSH server daemon (sshd) are not affected. V. Solution Perform one of the following: 1) Upgrade your vulnerable system to a supported FreeBSD stable or release / security branch (releng) dated after the correction date. 2) To update your vulnerable system via a source code patch: The following patches have been verified to apply to the applicable FreeBSD release branches. a) Download the relevant patch from the location below, and verify the detached PGP signature using your PGP utility. # fetch http://security.FreeBSD.org/patches/SA-13:14/openssh.patch # fetch http://security.FreeBSD.org/patches/SA-13:14/openssh.patch.asc # gpg --verify openssh.patch.asc b) Execute the following commands as root: # cd /usr/src # patch < /path/to/patch Recompile the operating system using buildworld and installworld as described in . Restart the sshd daemon, or reboot the system. 3) To update your vulnerable system via a binary patch: Systems running a RELEASE version of FreeBSD on the i386 or amd64 platforms can be updated via the freebsd-update(8) utility: # freebsd-update fetch # freebsd-update install VI. Correction details The following list contains the correction revision numbers for each affected branch. Branch/path Revision - ------------------------------------------------------------------------- stable/10/ r258335 - ------------------------------------------------------------------------- To see which files were modified by a particular revision, run the following command, replacing NNNNNN with the revision number, on a machine with Subversion installed: # svn diff -cNNNNNN --summarize svn://svn.freebsd.org/base Or visit the following URL, replacing NNNNNN with the revision number: VII. References The latest revision of this advisory is available at -----BEGIN PGP SIGNATURE----- iQIcBAEBCgAGBQJSl+hmAAoJEO1n7NZdz2rnHMYP/3yEQldDKONpQ1zS5YfDyVwO wRBTgxMST7ozg/y7/xBA9FIpdRB8fJOgijKKVQv02MCN5xM5mXexxZAu1X3gcWls v8Tf1YogR0IzLKzFDYYqZ/gWg/5vK1ALzPbHRSmDYivUSOyJftvDNFzPZnFp4DsI U30OGxBfLSOvvX5XNGSixmILzv5DLxe7ThGa36oIZCKUAXSrNm79NfGiI0EvXK2Y R3nTjdd5r5F5/K5S59BMmAmKCGIqsTJ/jeICKe49VUK+YyD+Wmr0gohhU6bmENWM aXAD9em+uKGZnlqBUr5YC4vv8NHWuhOTWfl1CTDH4QhFOP+hiJt2w4EvGYORL1R/ 2VDmFtiiPeebi7ECSTOSudx/xGvycpnUspw4T/b+H+kGar1ZvHpwqRYDC/Wla5Vq Uzi7uIWTdJieLQXRERTln8mtehYmfHurlu1Mltb0v35vkSyUV5V6RjtxRAi0sWbj w1A0lpDga1lom1FI5JTsiGtwV8A3MbmFKLuK7EUQf8I8lS80SptJNMMTkzYeW/Zy jVqSj63Ns3WaDeHMURYfxf2ppb3meBX+Tw0glTBFJlE46c/sZ01zmcM0q1jQk5Vn nHZgnGTKsCqR1VlnARdDicfa3VVhcPxeUkGEALZv1m31jA0AYG7BeAX9pvoQoOGK 1Oeu9j2MeszutBto6gqh =6vNc -----END PGP SIGNATURE-----