Date: Thu, 27 May 2004 19:36:16 -0400
From: CERT Advisory <[email protected]>
To: [email protected]Subject: US-CERT Technical Cyber Security Alert TA04-147A -- CVS Heap Overflow Vulnerability
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Technical Cyber Security Alert TA04-147A
CVS Heap Overflow Vulnerability
Original release date: May 26, 2004
Last revised: --
Source: US-CERT
Systems Affected
* Concurrent Versions System (CVS) versions prior to 1.11.16
* CVS Features versions prior to 1.12.8
Overview
A heap overflow vulnerability in the Concurrent Versions System (CVS)
could allow a remote attacker to execute arbitrary code on a
vulnerable system.
I. Description
CVS is a source code maintenance system that is widely used by
open-source software development projects. There is a heap memory
overflow vulnerability in the way CVS handles the insertion of
modified and unchanged flags within entry lines. When processing an
entry line, an additional byte of memory is allocated to flag the
entry as modified or unchanged. There is a failure to check if a byte
has been previously allocated for the flag, which creates an
off-by-one buffer overflow. By calling a vulnerable function several
times and inserting specific characters into the entry lines, a remote
attacker could overwrite multiple blocks of memory. In some
environments, the CVS server process is started by the Internet
services daemon (inetd) and may run with root privileges.
An authenticated client could exploit this vulnerability to execute
arbitrary code, execute commands, modify sensitive information, or
cause a denial of service. Note that if a CVS server is configured to
permit anonymous read-only access, then this provides sufficient
access to exploit a vulnerable server, as anonymous users are
authenticated through the cvspserver process.
US-CERT is tracking this issue as VU#192038. This reference number
corresponds to CVE candidate CAN-2004-0396.
II. Impact
An authenticated client could exploit this vulnerability to execute
arbitrary code on the vulnerable system with the privileges of the CVS
server process. It is possible for an anonymous user with read-only
access to exploit a vulnerable server as they are authenticated
through the cvspserver process.
In addition to compromising the system running CVS, there is a
significant secondary impact in that source code maintained in CVS
repositories could be modified to include Trojan horses, backdoors, or
other malicious code.
III. Solution
Apply Patch or Upgrade
Apply the appropriate patch or upgrade as specified by your vendor.
For vendor specific responses, please see your vendor's website or
Vulnerability Note VU#192038.
This issue has been resolved in Stable CVS Version 1.11.16 and CVS
Feature Version 1.12.8.
Disable CVS Server
Until a patch or upgrade can be applied, consider disabling the CVS
server.
Block or Restrict Access
Block or restrict access to the CVS server from untrusted hosts and
networks. The CVS server typically listens on 2401/tcp, but may use
another port or protocol.
Limit CVS Server Privileges
* Configure CVS server to run in a restricted (chroot) environment.
* Run CVS servers with the minimum set of privileges required on the
host file system.
* Provide separate systems for development (write) and
public/anonymous (read-only) CVS access.
* Host public/anonymous CVS servers on single-purpose, secured
systems.
Note that some of these workarounds will only limit the scope and
impact of possible attacks. Note also that anonymous (read-only)
access is sufficent to exploit this vulnerability.
Appendix B. References
* http://security.e-matters.de/advisories/072004.html
* http://secunia.com/advisories/11641/
* http://www.securitytracker.com/alerts/2004/May/1010208.html
* http://www.netsys.com/library/papers/chrooted-ssh-cvs-server.txt
_________________________________________________________________
US-CERT thanks Stefan Esser of e-matters for reporting this problem
and for information used to construct this advisory.
_________________________________________________________________
Feedback can be directed to the authors: Jason A. Rafail and
Damon Morda
_________________________________________________________________
The latest version of this document can be found at:
<http://www.us-cert.gov/cas/techalerts/TA04-147A.html>;
_________________________________________________________________
Copyright 2004 Carnegie Mellon University.
Terms of use:
<http://www.us-cert.gov/legal.html>;
_________________________________________________________________
Revision History
May 26, 2004: Initial release
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