FreeBSD Security Advisory FreeBSD-SA-16:14.openssh

Fabricante: FreeBSD
Fecha: 17/03/2016
Identificador: FreeBSD-SA-16:14.openssh
FreeBSD Security Advisory FreeBSD-SA-16:14.openssh
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA512 ============================================================================= FreeBSD-SA-16:14.openssh Security Advisory The FreeBSD Project Topic: OpenSSH xauth(1) command injection Category: contrib Module: OpenSSH Announced: 2016-03-16 Credits: Affects: All supported versions of FreeBSD. Corrected: 2016-03-12 23:53:20 UTC (stable/10, 10.2-STABLE) 2016-03-14 13:05:13 UTC (releng/10.3, 10.3-RC2) 2016-03-16 22:31:04 UTC (releng/10.2, 10.2-RELEASE-p14) 2016-03-16 22:30:56 UTC (releng/10.1, 10.1-RELEASE-p31) 2016-03-13 23:50:19 UTC (stable/9, 9.3-STABLE) 2016-03-16 22:30:03 UTC (releng/9.3, 9.3-RELEASE-p39) CVE Name: CVE-2016-3115 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. OpenSSH supports X11 forwarding, allowing X11 applications on the server to connect to the client's display. When an X11 forwarding session is established, the OpenSSH daemon runs the xauth tool with information provided by the client to create an authority file on the server containing information that applications need in order to connect to the client's X11 display. II. Problem Description Due to insufficient input validation in OpenSSH, a client which has permission to establish X11 forwarding sessions to a server can piggyback arbitrary shell commands on the data intended to be passed to the xauth tool. III. Impact An attacker with valid credentials and permission to establish X11 forwarding sessions can bypass other restrictions which may have been placed on their account, for instance using ForceCommand directives in the server's configuration file. IV. Workaround Disable X11 forwarding globally by adding the following line to /etc/ssh/sshd_config, before any Match blocks: X11Forwarding no then either restart the OpenSSH daemon or reboot the system. Consult the sshd(8) and sshd_config(5) manual pages for additional information on how to enable or disable X11 forwarding on a per-user or per-key basis. 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, then either restart the OpenSSH daemon or reboot the system. 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 # service sshd restart 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. # fetch https://security.FreeBSD.org/patches/SA-16:14/openssh-xauth.patch # fetch https://security.FreeBSD.org/patches/SA-16:14/openssh-xauth.patch.asc # gpg --verify openssh-xauth.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 . d) Either restart the OpenSSH daemon or reboot the system. VI. Correction details The following list contains the correction revision numbers for each affected branch. Branch/path Revision - ------------------------------------------------------------------------- stable/9/ r296780 releng/9.3/ r296953 stable/10/ r296781 releng/10.1/ r296954 releng/10.2/ r296955 releng/10.3/ r296853 - ------------------------------------------------------------------------- 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----- iQIcBAEBCgAGBQJW6em1AAoJEO1n7NZdz2rnbQEP/2juxLcCzeHBUfVMBF6/HebX Rt72Okdpkeht1FOVAnfJsG1l/zCJhS8RhKVG62KM9nK9Dl83NhLpobVMAhbDtzF/ Sr6f8UYZi22/0OlLsMBrYWeV1C8s6W/5z/d5OeomdHug6g6nFRi2g+tW6NImyU98 YdvgeFLcZKKFy2rbeA1lgXhC7TegKhr3ZbzisEFfkMR+eRYs+3lqaXMAr8RUy3XS RNQBQ5WBfxR1Ld+ISeGjjVYpGU6PG8aY4qFsdGF2yWOBq4hk1NbrPFamVyAVd8g3 PsApqbvIsK8VjPAvxiwxOEfARRxIXsqOu8FcLwkpZ73/pj4vA8DjUSz9knhqhUyF sCaOZxvOSJ5iU4JEB/Lva2jwNiY+6wQa6GXhCTlriV6PZZbhrAl5yzd9Z6jvYHsQ sNx6a9/CjLw1L5Rthe3Ot3lVdnZeKq03tKjV88QFYj8+GhZFTnIjGAkPc+HIONdS SxIhuHTrGGR4bj0XC7EC06ElSlt8oZjTpwKAFRetsJ3Z/DN5P0+HA6GR+5Nk/H2f soP96pmrCNP3DPGNmTuzzGOYR7esTR0tC2d8ebit0kiPwcbQ8x2Bic1hdh2Dc7s8 vDAdxq3nPBHySvCiqt+G1faIA6HfECymhhqhC1bkJe046DQOEAdslhdNUhIBOE/x yFRqqetd9LHhZBI9tGmF =eliH -----END PGP SIGNATURE-----