Multiple AV Vendor Incorrect CRC32 BypassVulnerability.

["Steve Scholz" <steve_scholz () sybari com>]

Hi Bipin,
 
Actually by removing the file name size you made the Eicar.com invalid.
 Antigen does scan this file and when it extracts the eicar.com.txt we get a 
eicar.com.txtX5O!P%@AP[4\PZX54(P^)7CC)7}$EICAR-STANDARD-ANTIVIRUS-TE in the 
text file rather then a valid eicar. Since you made the name length a zero 
when pasred the name of the zipped file becomes part of the file and the 
info at the end is truncated making the file if it was viral, non-viral or 
if it were able to be executed after this process is done it would be an 
invalid application and it would not be executed. I used ziprepairpro and 
came up with the same results.
 
If a file filter is set up for exe, pif ,scr ect we will remove the file 
from the zip and rewrite it with a txt file that can be extracted and read. 
If a doc file is put into a zip of this nature with an embedded eicar in it 
we do detect the ecar as long as there is info after the embedded file to be 
truncated.

 
 
 
Steve Scholz
Corporate Sales Engineer-North America
Sybari Software, Inc.
631-630-8556 Direct
516-903-2464 Mobile
Email:  Steve_scholz () sybari com
MSN IM:Steve_Scholz () Msn com (email never checked) 

 
-----Original Message-----
From: full-disclosure-bounces () lists grok org uk
[mailto:full-disclosure-bounces () lists grok org uk] On Behalf Of bipin gautam
Sent: Wednesday, March 09, 2005 9:37 PM
To: full-disclosure () lists grok org uk
Cc: vuln () secunia com
Subject: [Full-disclosure] Multiple AV Vendor Incorrect CRC32 BypassVulnerability.
 
 
Multiple AV Vendor Incorrect CRC32 Bypass Vulnerability.
 
Affected Product:
AVG 718
Sybari (Antigen for M$ exchange) 7.5.1314 Symantec 8.0 McAfee 4442 BitDefender 7.0
 
 
Description:
if you create a zip archive with invalid CRC checksum...... some AV skip scanning the archive marking it as 
clean........ by this way, you can bypass antivirus gateways and slip in any attachment without scanning the archive. 
Moreover, these days....
software tools automatically repair a *broken* archive.
 
Vendor notification: I've lost faith in responsible disclosure... long ago! Moreover, vendors don't respond in timely 
manner.
 
regards,
Bipin Gautam
http://www.geocities.com/visitbipin/
 
 
Disclaimer: The information in the advisory is believed to be accurate at the time of printing 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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