[squid-users] blocking certain file types by content

Yuri Voinov yvoinov at gmail.com
Sun Dec 13 18:32:55 UTC 2015

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For malware checking we have two working (and performance) solutions:


No need to block any and all executables in the world. Just enough to
check it with AV-engine. ;)

13.12.15 18:31, Markus пишет:
> I'm wondering if it is possible to detect (and block) certain files by
> its header/content  like 'MZ' (0d 0a 0d 0a 4d 5a) which is a beginning
> of any EXE/DLL file.
> Purpose:
> I'm trying to protect my internal network against unconsciously
> downloading executable files (like malware). All users traffic pass
> through our Squid proxy.
> What I've already done is:
> 1. Blocking by URL (url contains \.exe \.dll and other banned extensions)
> 2. Blocking by server's response header (MIME-type ,
> Content-Disposition and so on.)
> But there is still a way to download an executable file when somebody
> put it on server as e.g. readme.txt. Server's response header would be
> in this case 'Content-Type: text/html;'.
> So none of above mentioned rules would block this file. Of course, a
> regular Web browser would show this EXE as text, which isn't
> dangerous. But we can imagine a dedicated downloader (e.g. a part of
> the malware) which can download binary code this way.
> So, tell me guys, if there is any solution for this?
> I could also use "Snort", but it would be very inflexible (I would
> like to have a whitelist of domains).
> even if it's possible, what about performance in real environment?
> maybe there's a way to analyze only the first bytes of the incoming
> stream?
> greetings
> Markus
> PS
> ----
> if the string 'MZ' is too short, we can also use 'This program cannot
> be run in DOS mode' (this string is also part of EXE header). But
> probably a majority of exe packers can compress it.
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