-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 ============================================================================= FreeBSD-SA-08:05.openssh Security Advisory The FreeBSD Project Topic: OpenSSH X11-forwarding privilege escalation Category: contrib Module: openssh Announced: 2008-04-17 Credits: Timo Juhani Lindfors Affects: All supported versions of FreeBSD Corrected: 2008-04-16 23:58:33 UTC (RELENG_7, 7.0-STABLE) 2008-04-16 23:58:52 UTC (RELENG_7_0, 7.0-RELEASE-p1) 2008-04-16 23:59:35 UTC (RELENG_6, 6.3-STABLE) 2008-04-16 23:59:48 UTC (RELENG_6_3, 6.3-RELEASE-p2) 2008-04-17 00:00:04 UTC (RELENG_6_2, 6.2-RELEASE-p12) 2008-04-17 00:00:28 UTC (RELENG_6_1, 6.1-RELEASE-p24) 2008-04-17 00:00:41 UTC (RELENG_5, 5.5-STABLE) 2008-04-17 00:00:54 UTC (RELENG_5_5, 5.5-RELEASE-p20) CVE Name: CVE-2008-1483 For general information regarding FreeBSD Security Advisories, including descriptions of the fields above, security branches, and the following sections, please visit . 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 OpenSSH server daemon (sshd) provides support for the X11 protocol by binding to a port on the server and forwarding any connections which are made to that port. II. Problem Description When logging in via SSH with X11-forwarding enabled, sshd(8) fails to correctly handle the case where it fails to bind to an IPv4 port but successfully binds to an IPv6 port. In this case, applications which use X11 will connect to the IPv4 port, even though it had not been bound by sshd(8) and is therefore not being securely forwarded. III. Impact A malicious user could listen for X11 connections on a unused IPv4 port, e.g tcp port 6010. When an unaware user logs in and sets up X11 fowarding the malicious user can capture all X11 data send over the port, potentially disclosing sensitive information or allowing the execution of commands with the privileges of the user using the X11 forwarding. NOTE WELL: FreeBSD ships with IPv6 enabled by default in the GENERIC and SMP kernels, so users are vulnerable even they have not explicitly enabled IPv6 networking. IV. Workaround Disable support for IPv6 in the sshd(8) daemon by setting the option "AddressFamily inet" in /etc/ssh/sshd_config. Disable support for X11 forwarding in the sshd(8) daemon by setting the option "X11Forwarding no" in /etc/ssh/sshd_config. V. Solution Perform one of the following: 1) Upgrade your vulnerable system to 5-STABLE, 6-STABLE, or 7-STABLE, or to the RELENG_7_0, RELENG_6_3, RELENG_6_2, RELENG_6_1, RELENG_5_5 security branch dated after the correction date. 2) To patch your present system: The following patch has been verified to apply to FreeBSD 5.5, 6.1, 6.2, 6.3, and 7.0 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-08:05/openssh.patch # fetch http://security.FreeBSD.org/patches/SA-08:05/openssh.patch.asc b) Execute the following commands as root: # cd /usr/src # patch < /path/to/patch # cd /usr/src/secure/lib/libssh # make obj && make depend && make && make install # cd /usr/src/secure/usr.sbin/sshd # make obj && make depend && make && make install # /etc/rc.d/sshd restart VI. Correction details The following list contains the revision numbers of each file that was corrected in FreeBSD. Branch Revision Path - ------------------------------------------------------------------------- RELENG_5 src/crypto/openssh/channels.c 1.18.2.1 RELENG_5_5 src/UPDATING 1.342.2.35.2.21 src/sys/conf/newvers.sh 1.62.2.21.2.22 src/crypto/openssh/channels.c 1.18.8.1 RELENG_6 src/crypto/openssh/channels.c 1.20.2.3 RELENG_6_3 src/UPDATING 1.416.2.37.2.6 src/sys/conf/newvers.sh 1.69.2.15.2.5 src/crypto/openssh/channels.c 1.20.2.2.4.1 RELENG_6_2 src/UPDATING 1.416.2.29.2.16 src/sys/conf/newvers.sh 1.69.2.13.2.15 src/crypto/openssh/channels.c 1.20.2.2.2.1 RELENG_6_1 src/UPDATING 1.416.2.22.2.27 src/sys/conf/newvers.sh 1.69.2.11.2.26 src/crypto/openssh/channels.c 1.20.2.1.4.1 RELENG_7 src/crypto/openssh/channels.c 1.23.2.1 RELENG_7_0 src/UPDATING 1.507.2.3.2.5 src/sys/conf/newvers.sh 1.72.2.5.2.5 src/crypto/openssh/channels.c 1.23.4.1 - ------------------------------------------------------------------------- VII. References http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=463011 http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2008-1483 http://www.openssh.com/txt/release-5.0 The latest revision of this advisory is available at http://security.FreeBSD.org/advisories/FreeBSD-SA-08:05.openssh.asc -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.7 (FreeBSD) iD8DBQFICXCKFdaIBMps37IRAnTEAJ9vVF3ShIpmOes+FB4TGzIZeBB85gCdFOc5 zHQV1Flg2JpAARha1Yz2q98= =P9XX -----END PGP SIGNATURE-----