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AUSCERT External Security Bulletin Redistribution
ESB-2008.0385 -- [Win][UNIX/Linux]
Multiple vulnerabilities in ClamAV
16 April 2008
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AusCERT Security Bulletin Summary
---------------------------------
Product: ClamAV
Publisher: iDEFENSE
Operating System: Windows
UNIX variants (UNIX, Linux, OSX)
Impact: Execute Arbitrary Code/Commands
Access: Remote/Unauthenticated
CVE Names: CVE-2008-0314
Original Bulletin:
http://labs.idefense.com/intelligence/vulnerabilities/display.php?id=686
http://labs.idefense.com/intelligence/vulnerabilities/display.php?id=687
Comment: This bulletin contains two (2) iDefense advisories. The first
vulnerability was reportedly fixed via the March virus-db
update. Both vulnerabilities are reportedly fixed in version
0.93. Users are encouraged to upgrade to this release.
- --------------------------BEGIN INCLUDED TEXT--------------------
iDefense Security Advisory 04.14.08
http://labs.idefense.com/intelligence/vulnerabilities/
Apr 14, 2008
I. BACKGROUND
Clam AntiVirus is a multi-platform GPL anti-virus toolkit. ClamAV is
often integrated into e-mail gateways and used to scan e-mail traffic
for viruses. It supports virus scanning for a wide variety of packed
Portable Executable (PE) binaries. PeSpin is one of the supported
packer/protectors. For more information visit the vendor's web site at
the following URL.
http://www.clamav.net/
II. DESCRIPTION
Remote exploitation of a heap overflow vulnerability in Clam AntiVirus'
ClamAV, as included in various vendors' operating system distributions,
allows attackers to execute arbitrary code with the privileges of the
affected process.
The vulnerability exists within the code responsible for decompressing
sections within a PE binary packed with the PeSpin executable
protector. See the following excerpt from libclamav/spin.c:
417 key32 = cli_readint32(ep+0x2fee);
...
427 cli_dbgmsg("spin: Resources (sect%d) appear to be
compressed\n\tuncompressed offset %x, len %x\n\tcompressed offset %x,
len %x\n", j, sections[j].rva, key32 - sections[j].rva, key32,
sections[j].vsz - (key32 - sections[j].rva));
428
429 if ( (curr=(char *)cli_malloc(sections[j].vsz)) != NULL ) {
430 memcpy(curr, src + sections[j].raw, key32 -
sections[j].rva); /* Uncompressed part */
431 memset(curr + key32 - sections[j].rva, 0, sections[j].vsz
- - (key32 - sections[j].rva)); /* bzero */
On line 417, a 32-bit value is read from the file into the "key32"
variable. Then a heap buffer is allocated using the "sections[j].vsz"
value on line 429. The "memcpy" call on line 430 then copies data into
the newly allocated buffer.
No validation is performed on the "key32", "sections[j].raw", and
"sections[j].rva" values before they are used in the memory copy
operation. Since these values are under attacker control, this can lead
to an exploitable heap corruption condition.
III. ANALYSIS
Exploitation of this vulnerability results in the execution of arbitrary
code with the privileges of the process using libclamav. In the case of
the clamd program, this will result in code execution with the
privileges of the clamav user. Unsuccessful exploitation results in the
clamd process crashing.
Although it would appear that the following "memset" call will cause a
DoS condition, iDefense Labs confirmed that it is possible to bypass
this call. This is accomplished through manipulating the file such that
the memory layout allows the "sections" structure to be completely
controlled via an overwrite by the "memcpy" call.
IV. DETECTION
iDefense has confirmed the existence of this vulnerability in ClamAV
0.92.1. Previous versions may also be affected.
V. WORKAROUND
Disabling the scanning of PE files will prevent exploitation.
If using clamscan, this can be done by running clamscan with the
'--no-pe' option.
If using clamdscan, set the 'ScanPE' option in the clamd.conf file to
'no'.
VI. VENDOR RESPONSE
The ClamAV team has addressed this vulnerability within version 0.93.
Additionally, the ClamAV team reports, "the vulnerable module was
remotely disabled via virus-db update in March."
VII. CVE INFORMATION
The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CVE-2008-0314 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
03/04/2008 Initial vendor notification
03/06/2008 Initial vendor response
04/14/2008 Coordinated public disclosure
IX. CREDIT
This vulnerability was reported to iDefense by Damian Put.
Get paid for vulnerability research
http://labs.idefense.com/methodology/vulnerability/vcp.php
Free tools, research and upcoming events
http://labs.idefense.com/
X. LEGAL NOTICES
Copyright © 2008 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 e-mail 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.
_______________________________________________
iDefense Security Advisory 04.14.08
http://labs.idefense.com/intelligence/vulnerabilities/
Apr 14, 2008
I. BACKGROUND
Clam AntiVirus is a multi-platform GPL anti-virus toolkit. ClamAV is
often integrated into e-mail gateways and used to scan e-mail traffic
for viruses. It supports virus scanning for a wide variety of packed
Portable Executable (PE) binaries. WWPack is one of the supported
packers. For more information visit the vendor's web site at the
following URL.
http://www.clamav.net/
II. DESCRIPTION
Remote exploitation of a heap overflow vulnerability in Clam AntiVirus'
ClamAV, as included in various vendors' operating system distributions,
allows attackers to execute arbitrary code with the privileges of the
affected process.
The vulnerability exists within the code responsible for reading in
sections within a PE binary packed with the WWPack executable
compressor. See the following excerpt from libclamav/pe.c:
1879 dsize = max-min+headsize-exe_sections[nsections - 1].rsz;
....
1883 if((dest = (char *) cli_calloc(dsize, sizeof(char))) ==
NULL) {
....
1897 for(i = 0 ; i < (unsigned int)nsections-1; i++) {
1898 if(exe_sections[i].rsz) {
1899 if(!cli_seeksect(desc, &exe_sections[i]) ||
(unsigned int) cli_readn(desc, dest + headsize + exe_sections[i].rva -
min, exe_sections[i].rsz) != exe_sections[i].rsz) {
The size of the allocated heap buffer is calculated on line 1879 using
several values that are under attacker control. The allocation takes
place on line 1883. Within the loop, starting on line 1897, data is
read into the allocated buffer (line 1899).
No validation is done to ensure that the resulting data is not written
outside the bounds of the "dest" buffer. The "headsize",
"exe_sections[i].rva", "min", and "exe_sections[i].rsz" values that are
used for this operation are all under attacker control. As such, an
exploitable heap corruption condition may occur.
III. ANALYSIS
Exploitation of this vulnerability results in the execution of arbitrary
code with the privileges of the process using libclamav. In the case of
the clamd program, this will result in code execution with the
privileges of the clamav user. Unsuccessful exploitation results in the
clamd process crashing.
IV. DETECTION
iDefense has confirmed the existence of this vulnerability in ClamAV
0.92.1. Previous versions may also be affected.
V. WORKAROUND
Disabling the scanning of PE files will prevent exploitation.
If using clamscan, this can be done by running clamscan with the
'--no-pe' option.
If using clamdscan, set the 'ScanPE' option in the clamd.conf file to
'no'.
VI. VENDOR RESPONSE
VII. CVE INFORMATION
A Mitre Corp. Common Vulnerabilities and Exposures (CVE) number has not
been assigned yet.
VIII. DISCLOSURE TIMELINE
03/04/2008 Initial vendor notification
03/06/2008 Initial vendor response
04/14/2008 Coordinated public disclosure
IX. CREDIT
This vulnerability was reported to iDefense by Damian Put and Thomas
Pollet.
Get paid for vulnerability research
http://labs.idefense.com/methodology/vulnerability/vcp.php
Free tools, research and upcoming events
http://labs.idefense.com/
X. LEGAL NOTICES
Copyright © 2008 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 e-mail 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.
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