-----BEGIN PGP SIGNED MESSAGE----- ============================================================================= FreeBSD-SA-02:41.smrsh Security Advisory The FreeBSD Project Topic: smrsh restrictions can be bypassed [REVISED] Category: core Module: contrib_sendmail Announced: 2002-11-15 Credits: zen-parse , Pedram Amini , iDEFENSE Affects: All releases prior to FreeBSD 4.7-RELEASE Corrected: 2002-10-08 00:53:31 UTC (RELENG_4) 2002-10-08 00:57:20 UTC (RELENG_4_7) 2002-10-26 21:11:30 UTC (RELENG_4_6) 2002-10-26 21:10:59 UTC (RELENG_4_5) 2002-10-26 21:10:22 UTC (RELENG_4_4) 2002-10-26 21:08:42 UTC (RELENG_4_3) FreeBSD only: NO 0. Revision History v1.0 2002-11-12 Initial release. v1.1 2002-11-15 Correct patch instructions. Update workaround. Add CVE reference. I. Background The sendmail Restricted Shell command (smrsh) is intended as a replacement for the system shell (/bin/sh) for use by sendmail. It limits the set of programs that can be executed through sendmail to those in a single directory, and limits shell built-in commands. II. Problem Description Errors in smrsh's handling of command arguments with "||" or spaces may allow the execution of commands outside of those in its target directory. Since command arguments may be specified in local users' `.forward' files, the smrsh restrictions may be bypassed using such files that are specially crafted. III. Impact Users with a local account and the ability to create or modify their `.forward' files can circumvent the smrsh restrictions. This is mostly of consequence to systems which have local users that are not normally allowed access to a login shell, as such users may abuse this bug in order to execute arbitrary commands with normal privileges. IV. Workaround [The workaround described in revision 1.0 of this advisory was effective, but disabled more functionality than was necessary.] Disable sendmail delivery to programs. To do so, add the following line to the sendmail.mc file, regenerate the sendmail.cf configuration file, and restart sendmail. MODIFY_MAILER_FLAGS(`LOCAL', `-|') V. Solution 1) Upgrade your vulnerable system to 4.7-STABLE; or to the RELENG_4_7, RELENG_4_6, RELENG_4_5, RELENG_4_4, or RELENG_4_3 security branch dated after the correction date. 2) To patch your present system: The following patch has been verified to apply to FreeBSD 4.4, FreeBSD 4.5, and FreeBSD 4.6 systems. a) Download the relevant patch from the location below, and verify the detached PGP signature using your PGP utility. [For FreeBSD 4.6 systems] # fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-02:41/smrsh.patch # fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-02:41/smrsh.patch.asc [For FreeBSD 4.3, 4.4, and 4.5 systems] # fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-02:41/smrsh2.patch # fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-02:41/smrsh2.patch.asc b) Execute the following commands as root: # cd /usr/src # patch < /path/to/patch [The following two steps apply only to FreeBSD 4.6 systems.] # cd /usr/src/lib/libsm # make depend && make # cd /usr/src/lib/libsmutil # make depend && make # cd /usr/src/libexec/smrsh # make depend && make && make install VI. Correction details The following list contains the revision numbers of each file that was corrected in FreeBSD. Path Revision Branch - ------------------------------------------------------------------------- src/contrib/sendmail/smrsh/smrsh.c RELENG_4 1.3.6.9 RELENG_4_7 1.3.6.8.2.1 RELENG_4_6 1.3.6.6.2.1 RELENG_4_5 1.3.6.5.4.1 RELENG_4_4 1.3.6.5.2.1 RELENG_4_3 1.3.6.4.2.1 - ------------------------------------------------------------------------- VII. References -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.1 (FreeBSD) iQCUAwUBPdUXEVUuHi5z0oilAQEIAQP49AjM5zG8qH0/XzOFA2IDBp5djGIs3H1R 2demoBwF4W71AiUXURZvMwNpqV6+gRenCaOAzMis2pyOkW9aheT+eGoL4YWjQR/E aQsuX0j3XgXEVss+wQ9DPgkS+IyiYkPMrjpCNJbkQHuhwAQJj9VXrs0pbvl5NQLv JUcPZ70k3Q== =k1dg -----END PGP SIGNATURE-----