FreeBSD Security Advisory FreeBSD-SA-11:09.pam_ssh

Fabricante: FreeBSD
Fecha: 23/12/2011
Identificador: FreeBSD-SA-11:09.pam
FreeBSD Security Advisory FreeBSD-SA-11:09.pam_ssh
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 ============================================================================= FreeBSD-SA-11:09.pam_ssh Security Advisory The FreeBSD Project Topic: pam_ssh improperly grants access when user account has unencrypted SSH private keys Category: contrib Module: pam Announced: 2011-12-23 Credits: Guy Helmer, Dag-Erling Smorgrav Affects: All supported versions of FreeBSD. Corrected: 2011-12-11 20:40:23 UTC (RELENG_7, 7.4-STABLE) 2011-12-23 15:00:37 UTC (RELENG_7_4, 7.4-RELEASE-p5) 2011-12-23 15:00:37 UTC (RELENG_7_3, 7.3-RELEASE-p9) 2011-12-11 20:38:36 UTC (RELENG_8, 8.2-STABLE) 2011-12-23 15:00:37 UTC (RELENG_8_2, 8.2-RELEASE-p5) 2011-12-23 15:00:37 UTC (RELENG_8_1, 8.1-RELEASE-p7) 2011-12-11 16:57:27 UTC (RELENG_9, 9.0-STABLE) 2011-12-11 17:32:37 UTC (RELENG_9_0, 9.0-RELEASE) For general information regarding FreeBSD Security Advisories, including descriptions of the fields above, security branches, and the following sections, please visit . I. Background The PAM (Pluggable Authentication Modules) library provides a flexible framework for user authentication and session setup / teardown. It is used not only in the base system, but also by a large number of third-party applications. Various authentication methods (UNIX, LDAP, Kerberos etc.) are implemented in modules which are loaded and executed according to predefined, named policies. These policies are defined in /etc/pam.conf, /etc/pam.d/, /usr/local/etc/pam.conf or /usr/local/etc/pam.d/. The base system includes a module named pam_ssh which, if enabled, allows users to authenticate themselves by typing in the passphrase of one of the SSH private keys which are stored in encrypted form in the their .ssh directory. Authentication is considered successful if at least one of these keys could be decrypted using the provided passphrase. By default, the pam_ssh module rejects SSH private keys with no passphrase. A "nullok" option exists to allow these keys. II. Problem Description The OpenSSL library call used to decrypt private keys ignores the passphrase argument if the key is not encrypted. Because the pam_ssh module only checks whether the passphrase provided by the user is null, users with unencrypted SSH private keys may successfully authenticate themselves by providing a dummy passphrase. III. Impact If the pam_ssh module is enabled, attackers may be able to gain access to user accounts which have unencrypted SSH private keys. IV. Workaround No workaround is available, but systems that do not have the pam_ssh module enabled are not vulnerable. The pam_ssh module is not enabled in any of the default policies provided in the base system. The system administrator can use the following procedure to inspect all PAM policy files to determine whether the pam_ssh module is enabled. If the following command produces any output, the system may be vulnerable: # egrep -r '^[^#].*\' /etc/pam.* /usr/local/etc/pam.* The following command will disable the pam_ssh module in all PAM policies present in the system: # sed -i '' -e '/^[^#].*pam_ssh/s/^/#/' /etc/pam.conf /etc/pam.d/* \ /usr/local/etc/pam.conf /usr/local/etc/pam.d/* V. Solution Perform one of the following: 1) Upgrade your vulnerable system to 7-STABLE or 8-STABLE, or to the RELENG_8_2, RELENG_8_1, RELENG_7_4, or RELENG_7_3 security branch 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 FreeBSD 7.4, 7.3, 8.2 and 8.1 systems. 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-11:09/pam_ssh.patch # fetch http://security.FreeBSD.org/patches/SA-11:09/pam_ssh.patch.asc b) Execute the following commands as root: # cd /usr/src # patch < /path/to/patch # cd /usr/src/lib/libpam/modules/pam_ssh # make obj && make depend && make && make install NOTE: On the amd64 platform, the above procedure will not update the lib32 (i386 compatibility) libraries. On amd64 systems where the i386 compatibility libraries are used, the operating system should instead be recompiled as described in 3) To update your vulnerable system via a binary patch: Systems running 7.4-RELEASE, 7.3-RELEASE, 8.2-RELEASE, or 8.1-RELEASE 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 revision numbers of each file that was corrected in FreeBSD. CVS: Branch Revision Path - ------------------------------------------------------------------------- RELENG_7 src/lib/libpam/modules/pam_ssh/pam_ssh.c 1.44.2.2 RELENG_7_4 src/UPDATING 1.507.2.36.2.7 src/sys/conf/newvers.sh 1.72.2.18.2.10 src/lib/libpam/modules/pam_ssh/pam_ssh.c 1.44.2.1.8.2 RELENG_7_3 src/UPDATING 1.507.2.34.2.11 src/sys/conf/newvers.sh 1.72.2.16.2.13 src/lib/libpam/modules/pam_ssh/pam_ssh.c 1.44.2.1.6.2 RELENG_8 src/lib/libpam/modules/pam_ssh/pam_ssh.c 1.45.2.3 RELENG_8_2 src/UPDATING 1.632.2.19.2.7 src/sys/conf/newvers.sh 1.83.2.12.2.10 src/lib/libpam/modules/pam_ssh/pam_ssh.c 1.45.2.2.4.2 RELENG_8_1 src/UPDATING 1.632.2.14.2.10 src/sys/conf/newvers.sh 1.83.2.10.2.11 src/lib/libpam/modules/pam_ssh/pam_ssh.c 1.45.2.2.2.2 RELENG_9 src/lib/libpam/modules/pam_ssh/pam_ssh.c 1.47.2.2 RELENG_9_0 src/lib/libpam/modules/pam_ssh/pam_ssh.c 1.47.2.1.2.2 - ------------------------------------------------------------------------- Subversion: Branch/path Revision - ------------------------------------------------------------------------- stable/7/ r228421 releng/7.4/ r228843 releng/7.3/ r228843 stable/8/ r228420 releng/8.2/ r228843 releng/8.1/ r228843 stable/9/ r228410 releng/9.0/ r228414 - ------------------------------------------------------------------------- VII. References The latest revision of this advisory is available at http://security.FreeBSD.org/advisories/FreeBSD-SA-11:09.pam_ssh.asc -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.18 (FreeBSD) iEYEARECAAYFAk70nOoACgkQFdaIBMps37JTSwCfS+bmWBxv5hote7Hrcl7VZjjk vKMAn116aLADxmdYsyZ5WdSrfFTRt3Xm =Y+ar -----END PGP SIGNATURE-----