full-disclosure - Multiple Vendor Anti-Virus Software DetectionEvasion Vulnerability through forged magic byte

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Date: Thu Oct 27 08:14:41 2005
From: andrey at securityelf.org (Andrey Bayora)
Subject: Multiple Vendor Anti-Virus Software
	DetectionEvasion Vulnerability through forged magic byte

I checked the "ZM" variant and got the same results as for "MZ" one.
Thus, I think that they indeed, detected as executables, but only AV vendor
can tell for sure.
Generally, there are many variants for this issue, as many various "magic
byte" variants exist.
In my case - I force AV to look at the TEXT file as to EXECUTABLE, but it's
possible that other "pairs" then txt<->exe exist as well.

Regards,
Andrey Bayora.



----- Original Message ----- 
From: "Eygene A. Ryabinkin" <rea@....mbslab.kiae.ru>
To: "Debasis Mohanty" <mail@...kingspirits.com>
Cc: "'Andrey Bayora'" <andrey@...urityelf.org>;
<full-disclosure@...ts.grok.org.uk>; <bugtraq@...urityfocus.com>
Sent: Thursday, October 27, 2005 8:25 AM
Subject: Re: [Full-disclosure] Multiple Vendor Anti-Virus Software
DetectionEvasion Vulnerability through forged magic byte


> > Especially in case of EXEs, AFAIK not all EXEs has the same 'MAGIC BYTE'
> > (MZ). MZ only appears in the first two bytes of Win32 executable files.
>
>  Just for the curiosity: if you'll change "MZ" to "ZM" then the 16-bit
> executables (MZ and NE executables) will still run and 32-bit (PE)
executables
> will execute their DOS stub part. It will be very interesting to check if
> such files will be detected as executables at all in all mentioned
antiviruses
> and what sections PE files will be examined.
>
>  The 'MZ' -> 'ZM' hack is the old feature of MS-DOS loader that still
lives in
> WinXP (at least, didn't tested others, but believe that they also carry
that
> feature). That's what is called 'interoperability between various
versions' ;)
> -- 
>  rea
>
>