Public Vulnerability Reports

Clam AntiVirus ClamAV MS-Expand File Handling DoS Vulnerability



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


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 %dn", desc);
        return CL_EMSCOMP;

      if((tmp = tmpfile()) == NULL) {
        cli_dbgmsg("SZDD: Can't generate temporary file.n");
        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.


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.


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

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


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.


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


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 (, which standardizes names for
security problems.


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


The discoverer of this vulnerability wishes to remain anonymous.

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Copyright © 2005 Verisign, Inc.

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