Re: blocking BHX files with MIME

Peter,

Good call.  A quick search suggests that BinHex is a form of 
UUencoding, ie. uuencode for Mac... so I agree the sig might miss 
some attachments.

I don't have any other samples, tho, and since my policy is to only 
filter on strings in use by malware, not the full set of theoretical 
strings malware might use, I don't think I'll change the sig just 
yet.

I don't filter on the full set because if the string is not in use, 
there's no need to slow my filter down looking for something that's 
not there.

You're right though, if some virus starts using 'begin 4', I will 
need to remove a few characters from the end of the string.  

Stu

On 17 May 2006 at 3:33, Peter Kosinar wrote:

> > YmVnaW4gNj
> 
> Is it really the BHX (=BinHex) file format? Decoding the MIME sequence 
> yields "begin 6" (+one incomplete character), which looks very similar to 
> the UUE format. If it is actually UUE, the signature might be a bit too 
> weak because a perfectly valid UUEncoded file could start with "begin 4" 
> or "begin 7" or any other octal digit, as the three octal digits following 
> "begin" specify the permissions of the encoded file.


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Stuart Udall
stuart [email protected] net - http://www.cyberdelix.net/

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 * Origin: lsi: revolution through evolution (192:168/0.2)