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
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http://labs.idefense.com
X. LEGAL NOTICES
Copyright (c) 2005 iDEFENSE, Inc.
Permission is granted for the redistribution of this alert
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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.
This archive was generated by hypermail 2.1.3 : Wed Jun 29 2005 - 10:23:37 PDT