Subject: Re: Multiple Vendor Anti-Virus Software Detection
Evasion Vulnerability through forged magic byte
From: "Andrey Bayora" <andrey () securityelf ! org>
Date: 2005-10-25 3:07:51
[...]
VULNERABLE vendors and software (tested):
[...]
3. eTrust CA (ver 7.0.1.4, engine 11.9.1, vir sig. 9229)
[...]
DESCRIPTION:
The problem exists in the scanning engine - in the routine that
determines the file type. If some file types (file types tested
are .BAT, .HTML and .EML) changed to have the MAGIC BYTE of the
EXE files (MZ) at the beginning, then many antivirus programs
will be unable to detect the malicious file. It will break the
normal flow of the antivirus scanning and many existent and
future viruses will be undetected.
Andrey,
Thank you for the report.
You are effectively altering existing viruses to the point that
AV scanners do not detect them. If your altered virus sample
still executes correctly, you have simply created a new virus
variant. If your altered virus sample does not execute properly,
you have created nothing more than a corrupt virus sample.
Consequently, the issue that you describe is *not* a
vulnerability issue, but rather just an example of a new variant
that has not yet been added to an AV vendor's database of "known
viruses".
Note that CA eTrust Antivirus, when running in Reviewer mode,
should already detect these new variants.
Regards,
Ken
Ken Williams ; Dir. Vuln Research
Computer Associates ; 0xE2941985
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