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ClamAV libclamav PE WWPack Heap Overflow Vulnerability
------------------------------------------------------------------------
SUMMARY
<http://www.clamav.net/> 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". 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.
DETAILS
Vulnerable Systems:
* ClamAV version 0.92.1
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.
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.
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'.
Disclosure Timeline:
03/04/2008 - Initial vendor notification
03/06/2008 - Initial vendor response
04/14/2008 - Coordinated public disclosure
ADDITIONAL INFORMATION
The information has been provided by iDefense Labs.
The original article can be found at:
<http://labs.idefense.com/intelligence/vulnerabilities/display.php?id=687>
http://labs.idefense.com/intelligence/vulnerabilities/display.php?id=687
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