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-----BEGIN PGP SIGNED MESSAGE----- =========================================================================== AUSCERT External Security Bulletin Redistribution ESB-2003.0069 -- FreeBSD-SA-03:01.cvs remotely exploitable vulnerability in cvs server 05 February 2003 =========================================================================== AusCERT Security Bulletin Summary --------------------------------- Product: cvs server Vendor: FreeBSD Operating System: All FreeBSD versions prior to 4.6-RELEASE-p7, 4.7-RELEASE-p4, and 5.0-RELEASE-p1 Linux UNIX Impact: Execute Arbitrary Code/Commands Access Required: Remote - --------------------------BEGIN INCLUDED TEXT-------------------- - -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 ============================================================================= FreeBSD-SA-03:01.cvs Security Advisory The FreeBSD Project Topic: remotely exploitable vulnerability in cvs server Category: contrib Module: contrib_cvs Announced: 2003-02-04 Credits: Stefan Esser <s.esser@e-matters.de> Affects: x`x`All FreeBSD versions prior to 4.6-RELEASE-p7, 4.7-RELEASE-p4, 5.0-RELEASE-p1 Corrected: 2003-01-21 22:26:46 UTC (RELENG_4) 2003-02-04 18:05:07 UTC (RELENG_5_0) 2003-02-04 18:07:20 UTC (RELENG_4_7) 2003-02-04 18:08:26 UTC (RELENG_4_6) FreeBSD only: NO I. Background The Concurrent Versions System (CVS) is a version control system. It may be used to access a repository locally, or to access a `remote repository' using several different methods, including `ext' (rsh), and `pserver' (password-authenticated server). When accessing a remote repository, the target machine runs the CVS server to fulfill client requests. II. Problem Description The implementation of the CVS server contains a programming error which can lead to a block of memory being freed more than once (i.e. a double-free bug). Separately, the CVS server allows clients with write access to specify arbitrary commands to execute as part of an update (update-prog) or commit (checkin-prog). This is a dangerous feature that is generally not needed: there are other, safer methods of triggering program execution. III. Impact An attacker may exploit the double-free bug in order to bypass write access checks. Combined with the update-prog/checkin-prog feature, the attacker may be able to execute arbitrary commands with the privileges of the CVS server. The impact is most severe when running the CVS server in `pserver' mode to provide read-only access to the world (anoncvs). IV. Workaround Do not use `pserver' mode directly. Instead, use one of the safer methods described in the following online resources: <URL:http://openbsd.sunsite.ualberta.ca/papers/anoncvs-paper.ps> <URL:http://www.netsys.com/library/papers/chrooted-ssh-cvs-server.txt> V. Solution 1) Upgrade your vulnerable system to 4.7-STABLE; or to the RELENG_4_7 (4.7-RELEASE-p4), RELENG_4_6 (4.6-RELEASE-p7), or RELENG_5_0 (5.0-RELEASE-p1) security branch dated after the correction date. 2) To patch your present system: The following patch has been verified to apply to FreeBSD 4.6, 4.7, and 5.0 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-03:01/cvs.patch # fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-03:01/cvs.patch.asc b) Execute the following commands as root: # cd /usr/src # patch < /path/to/patch # cd /usr/src/gnu/usr.bin/cvs # make obj && 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/cvs/src/server.c RELENG_5_0 1.17.2.1 RELENG_4_7 1.13.2.2.6.1 RELENG_4_6 1.13.2.2.4.1 - - ------------------------------------------------------------------------- VII. References <URL:http://online.securityfocus.com/archive/1/72584> <URL:http://security.e-matters.de/advisories/012003.html> <URL:http://ccvs.cvshome.org/servlets/NewsItemView?newsID=51> <URL:http://www.kb.cert.org/vuls/id/650937> - -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.1 (FreeBSD) iD8DBQE+QAU9FdaIBMps37IRAvYzAKCeaZ1eWwiWNxRqgNRwnn4TwuwPPACdGF8T 0Ym2kCQxU0sJSRxmgAA/yM4= =9+5m - -----END PGP SIGNATURE----- - --------------------------END INCLUDED TEXT-------------------- You have received this e-mail bulletin as a result of your organisation's registration with AusCERT. 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On call after hours for member emergencies only. -----BEGIN PGP SIGNATURE----- Version: 2.6.3i Charset: noconv Comment: http://www.auscert.org.au/render.html?it=1967 iQCVAwUBPkD3rih9+71yA2DNAQFuHAP/V7hiHVAgfZL/P887lJac45urPhGSbvqh 9VX0utX9UKZjBRpwlIBrc6JpFL+fSt/pW3dMt7dYTCx6i5MUt3iJ0vrAU3HF+Eg4 poAeWIKmVbNfDlb538dKDds2ZtXZrDTmZIz5pd+er9gvIzW5PdnkKbRSUY6h/8UQ pU0rLP6aqWU= =VQ7i -----END PGP SIGNATURE-----