-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA512 ============================================================================= FreeBSD-SA-15:16.openssh Security Advisory The FreeBSD Project Topic: OpenSSH multiple vulnerabilities Category: contrib Module: openssh Announced: 2015-07-28, revised on 2015-07-30 Affects: All supported versions of FreeBSD. Corrected: 2015-07-28 19:58:44 UTC (stable/10, 10.2-PRERELEASE) 2015-07-28 19:58:44 UTC (stable/10, 10.2-BETA2-p2) 2015-07-28 19:59:04 UTC (releng/10.2, 10.2-RC1-p1) 2015-07-28 19:59:11 UTC (releng/10.1, 10.1-RELEASE-p16) 2015-07-28 19:58:54 UTC (stable/9, 9.3-STABLE) 2015-07-28 19:59:22 UTC (releng/9.3, 9.3-RELEASE-p21) 2015-07-30 10:09:07 UTC (stable/8, 8.4-STABLE) 2015-07-30 10:09:31 UTC (releng/8.4, 8.4-RELEASE-p36) CVE Name: CVE-2014-2653, CVE-2015-5600 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 2015-07-28 Initial release. v1.1 2015-07-30 Revised patch for FreeBSD 8.x to address regression when keyboard interactive authentication is used. v1.2 2015-07-30 Revised for typos. 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. The security of the SSH connection relies on the server authenticating itself to the client as well as the user authenticating itself to the server. SSH servers uses host keys to verify their identity. RFC 4255 has defined a method of verifying SSH host keys using Domain Name System Security (DNSSEC), by publishing the key fingerprint using DNS with "SSHFP" resource record. RFC 6187 has defined methods to use a signature by a trusted certification authority to bind a given public key to a given digital identity with X.509v3 certificates. The PAM (Pluggable Authentication Modules) library provides a flexible framework for user authentication and session setup / teardown. OpenSSH uses PAM for password authentication by default. II. Problem Description OpenSSH clients does not correctly verify DNS SSHFP records when a server offers a certificate. [CVE-2014-2653] OpenSSH servers which are configured to allow password authentication using PAM (default) would allow many password attempts. III. Impact A malicious server may be able to force a connecting client to skip DNS SSHFP record check and require the user to perform manual host verification of the host key fingerprint. This could allow man-in-the-middle attack if the user does not carefully check the fingerprint. [CVE-2014-2653] A remote attacker may effectively bypass MaxAuthTries settings, which would enable them to brute force passwords. [CVE-2015-5600] IV. Workaround Systems that do not use OpenSSH are not affected. There is no workaround for CVE-2014-2653, but the problem only affects networks where DNSsec and SSHFP is properly configured. Users who uses SSH should always check server host key fingerprints carefully when prompted. System administrators can set: UsePAM no In their /etc/ssh/sshd_config and restart sshd service to workaround the problem described as CVE-2015-5600 at expense of losing features provided by the PAM framework. We recommend system administrators to disable password based authentication completely, and use key based authentication exclusively in their SSH server configuration, when possible. This would eliminate the possibility of being ever exposed to password brute force attack. 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. SSH service has to be restarted after the update. A reboot is recommended but not required. 2) 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 SSH service has to be restarted after the update. A reboot is recommended but not required. 3) 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. [FreeBSD 9.3, 10.1, 10.2] # fetch https://security.FreeBSD.org/patches/SA-15:16/openssh.patch # fetch https://security.FreeBSD.org/patches/SA-15:16/openssh.patch.asc # gpg --verify openssh.patch.asc [FreeBSD 8.4] # fetch https://security.FreeBSD.org/patches/SA-15:16/openssh-8.patch # fetch https://security.FreeBSD.org/patches/SA-15:16/openssh-8.patch.asc # gpg --verify openssh-8.patch.asc # fetch https://security.FreeBSD.org/patches/SA-15:16/openssh-8-errata.patch # fetch https://security.FreeBSD.org/patches/SA-15:16/openssh-8-errata.patch.asc # gpg --verify openssh-8-errata.patch.asc b) Apply the patch. Execute the following commands as root: # cd /usr/src # patch < /path/to/patch c) Recompile the operating system using buildworld and installworld as described in . Restart the SSH service, or reboot the system. VI. Correction details The following list contains the correction revision numbers for each affected branch. Branch/path Revision - ------------------------------------------------------------------------- stable/8/ r286067 releng/8.4/ r286068 stable/9/ r285977 releng/9.3/ r285980 stable/10/ r285976 releng/10.1/ r285979 releng/10.2/ r285978 - ------------------------------------------------------------------------- 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----- Version: GnuPG v2.1.6 (FreeBSD) iQIcBAEBCgAGBQJVulgaAAoJEO1n7NZdz2rnhdMP/3d3HYI6Rz+1jLhRB5WhwVg5 2z16m5KAabsL3QZuTItZ5gv2DB4b3BjP91kIhAS5WSpyPU503N1OhxhyhEmRPeGJ Sf0oX54/uFDg8dHhLt2FHT+ebtndHYy+jqfOODZmf4CotCqeEVXnBDzeaYq4iAvY 6UHFu3n8UPdooNWfG+20Tfo9gOkM65rczODjOt1tPICK0oar07xVlLcC5UBdYQuT ztNg42lmXjftS5hGifo4uuGeeqaI+0uB3LcMo9WCYFo2kwMVghNIQUcCWnDDqZ6h 2Ci4Ho4N6FXiQnJ8d4Zwo6+cESeFhqDrPsO6KmeourVwiH8TXUTNxxm5o7fC+clL 3d7vsckBYPZdHKZb+E3SktjPTHaEXGrKMq24rwCTWf9GzvHVAehOEzYUPssR55lg q7O6SoaWmSsa7uxYdyj1ZKQRYfVkVV8I7kfV9z56ZUngPaJySA145LHuC8G2Hbm5 YAFCsGgsrSSycWJNqAeFsNFdq9BWvbl2UdvR4lgXDN8Fty0fTqEKyq6qwDj3uDul 1NzGijH5GyhR3PEUBgGYNL1RvmL9FY+47HAqLXTfadypevozQqwUCIIN329uJPZ/ VTQte7DQmMvwlDus5ihCLZ3/hfR/54Fixo7FkwCud+YBRmgeG9SnIuCNaX4nZB6R gzAUSqUVcWz7N1/nyns8 =qKoP -----END PGP SIGNATURE-----