Protect yourself against future threats.
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AUSCERT External Security Bulletin Redistribution
ESB-2002.629 -- FreeBSD-SA-02:41.smrsh
smrsh restrictions can be bypassed
13 November 2002
===========================================================================
AusCERT Security Bulletin Summary
---------------------------------
Product: smrsh (sendmail Restricted Shell command)
Vendor: FreeBSD
Operating System: FreeBSD prior to 4.7-RELEASE
Impact: Execute Arbitrary Code/Commands
Access Required: Existing Account
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FreeBSD-SA-02:41.smrsh Security Advisory
The FreeBSD Project
Topic: smrsh restrictions can be bypassed
Category: core
Module: contrib_sendmail
Announced: 2002-11-12
Credits: zen-parse <zen-parse@gmx.net>,
Pedram Amini <pamini@idefense.com>,
iDEFENSE <URL:http://www.idefense.com/>
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
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
There is no known workaround, short of disabling `.forward' files. To
do so, add the following line to the sendmail.mc file, regenerate the
sendmail.cf configuration file, and restart sendmail.
define(`confFORWARD_PATH', `')dnl
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.
# 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
b) Execute the following commands as root:
# cd /usr/src
# patch < /path/to/patch
# cd /usr/src/usr.sbin/sendmail
# 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
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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
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VII. References
<URL:http://www.idefense.com/advisory/10.01.02.txt>
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