Operating System:

Published:

30 June 2005

Protect yourself against future threats.

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

===========================================================================
             AUSCERT External Security Bulletin Redistribution

           ESB-2005.0484 -- iDEFENSE Security Advisory 06.29.05
      Clam AntiVirus ClamAV MS-Expand File Handling DoS Vulnerability
                               30 June 2005

===========================================================================

        AusCERT Security Bulletin Summary
        ---------------------------------

Product:           Clam AV 0.86 and prior
Publisher:         iDEFENSE
Operating System:  Linux variants
                   UNIX variants
Impact:            Denial of Service
Access:            Remote/Unauthenticated
CVE Names:         CAN-2005-1922

Original Bulletin: http://www.idefense.com/application/poi/display?id=276

- --------------------------BEGIN INCLUDED TEXT--------------------

Clam AntiVirus ClamAV MS-Expand File Handling DoS Vulnerability 

iDEFENSE Security Advisory 06.29.05
www.idefense.com/application/poi/display?id=276&type=vulnerabilities
June 29, 2005

I. BACKGROUND

Clam AntiVirus is a GPL anti-virus toolkit for Unix.

II. DESCRIPTION

Remote exploitation of an input validation error in Clam AntiVirus 
ClamAV allows attackers to cause a denial of service condition. 

The vulnerability specifically exists due to improper behavior during 
exceptional conditions. The following piece of code from 
libclamav/scanners.c shows where the vulnerability exists: 


    static int cli_scanszdd(...)
    {
      [...]
      FILE *tmp = NULL, *in;

      cli_dbgmsg("in cli_scanmscomp()\n");

      if((in = fdopen(dup(desc), "rb")) == NULL) {
        cli_dbgmsg("SZDD: Can't open descriptor %d\n", desc);
        return CL_EMSCOMP;
      }

      if((tmp = tmpfile()) == NULL) {
        cli_dbgmsg("SZDD: Can't generate temporary file.\n");
        fclose(in);
        return CL_ETMPFILE;
      }

      if(cli_msexpand(in, tmp) == -1) {
        cli_dbgmsg("SZDD: msexpand failed.\n");
        return CL_EMSCOMP;
      }

      [...]
    }


Each time the cli_msexpand() function fails , two file descriptors ('in'

and 'tmp') are leaked. As they are both opened using fopen(), there is 
also a memory leak (2 * 364 bytes). This allows an attacker to exhaust 
all of the available file descriptors fairly quickly with around 1,000 
malformed files.

III. ANALYSIS

Successful exploitation allows attackers to exhaust file descriptors 
pool and memory. Anti-virus detection functionality will fail if there 
is no file descriptors available with which to open files. Remote 
exploitation can be achieved by sending a malicious file in an e-mail 
message or during an HTTP session.

IV. DETECTION

iDEFENSE has confirmed the existence of this vulnerability in ClamAV 
0.83. It is suspected that all versions of ClamAV prior to 0.86 are
vulnerable. 

The following vendors distribute susceptible ClamAV packages within 
their respective operating system distributions:

	FreeBSD Project: FreeBSD 5.4 and prior
	Gentoo Foundation Inc.: Gentoo Linux 1.1a, 1.2, 1.4, 2004.0,
2004.1
     and 2004.2
	Mandrakesoft SA: Mandrakelinux 10.1 and Corporate Server 3.0
	Novell Inc.: SuSE Linux 9.1, 9.2 

V. WORKAROUND

As a temporary workaround solution, scanning of archive files can be 
disabled by supplying the --no-archive flag; however, this will 
significantly impact the effectiveness of the AV engine.

VI. VENDOR RESPONSE

This vulnerability has been patched in clamav 0.86 which is available
for download at:

   http://www.clamav.net/stable.php#pagestart

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CAN-2005-1922 to this issue. This is a candidate for inclusion in
the CVE list (http://cve.mitre.org), which standardizes names for
security problems.

VIII. DISCLOSURE TIMELINE

06/07/2005  Initial vendor notification
06/08/2005  Initial vendor response
06/29/2005  Public disclosure

IX. CREDIT

The discoverer of this vulnerability wishes to remain anonymous.

Get paid for vulnerability research
http://www.idefense.com/poi/teams/vcp.jsp

Free tools, research and upcoming events
http://labs.idefense.com

X. LEGAL NOTICES

Copyright (c) 2005 iDEFENSE, Inc.

Permission is granted for the redistribution of this alert
electronically. It may not be edited in any way without the express
written consent of iDEFENSE. If you wish to reprint the whole or any
part of this alert in any other medium other than electronically, please
email customerservice@idefense.com for permission.

Disclaimer: The information in the advisory is believed to be accurate
at the time of publishing based on currently available information. Use
of the information constitutes acceptance for use in an AS IS condition.
There are no warranties with regard to this information. Neither the
author nor the publisher accepts any liability for any direct, indirect,
or consequential loss or damage arising from use of, or reliance on,
this information.



- --------------------------END INCLUDED TEXT--------------------

You have received this e-mail bulletin as a result of your organisation's
registration with AusCERT. The mailing list you are subscribed to is
maintained within your organisation, so if you do not wish to continue
receiving these bulletins you should contact your local IT manager. If
you do not know who that is, please send an email to auscert@auscert.org.au
and we will forward your request to the appropriate person.

NOTE: Third Party Rights
This security bulletin is provided as a service to AusCERT's members.  As
AusCERT did not write the document quoted above, AusCERT has had no control
over its content. The decision to follow or act on information or advice
contained in this security bulletin is the responsibility of each user or
organisation, and should be considered in accordance with your organisation's
site policies and procedures. AusCERT takes no responsibility for consequences
which may arise from following or acting on information or advice contained in
this security bulletin.

NOTE: This is only the original release of the security bulletin.  It may
not be updated when updates to the original are made.  If downloading at
a later date, it is recommended that the bulletin is retrieved directly
from the author's website to ensure that the information is still current.

Contact information for the authors of the original document is included
in the Security Bulletin above.  If you have any questions or need further
information, please contact them directly.

Previous advisories and external security bulletins can be retrieved from:

        http://www.auscert.org.au/render.html?cid=1980

If you believe that your computer system has been compromised or attacked in 
any way, we encourage you to let us know by completing the secure National IT 
Incident Reporting Form at:

        http://www.auscert.org.au/render.html?it=3192

===========================================================================
Australian Computer Emergency Response Team
The University of Queensland
Brisbane
Qld 4072

Internet Email: auscert@auscert.org.au
Facsimile:      (07) 3365 7031
Telephone:      (07) 3365 4417 (International: +61 7 3365 4417)
                AusCERT personnel answer during Queensland business hours
                which are GMT+10:00 (AEST).
                On call after hours for member emergencies only.
===========================================================================

-----BEGIN PGP SIGNATURE-----
Comment: http://www.auscert.org.au/render.html?it=1967

iQCVAwUBQsOSRSh9+71yA2DNAQIKuwQAhASgh8UdbX6+9XvDGBVqmezHKzMTxTtI
AIzLrSaVgHFgwb7fd8A0JzZ8aQdDO6yd3ONgju8udxDF5GaS4bpOa5JXgHCJoi9I
YTrvAKriI/KckuLHmr+2eqw9/aZE2gsWrdqkOXK8YMrixRSxT92WsrID47Ph7Jgc
HEK4XfoCmBk=
=GbDM
-----END PGP SIGNATURE-----