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Re: UTF-8 BOM
From: rmkml <rmkml () yahoo fr>
Date: Tue, 9 Apr 2013 21:06:05 +0200 (CEST)

Hi,

Thx for sharing,

-maybe change B4 to 4B ?

-for http sig, maybe add H on pcre ?

Best Regards
Rmkml


On Mon, 8 Apr 2013, Joel Esler wrote:

On Apr 8, 2013, at 4:22 PM, James Lay <jlay () slave-tothe-box net> wrote:
      On 2013-04-08 14:10, Joel Esler wrote:
            How about something like this James?  (Three rules)

            alert tcp $EXTERNAL_NET any -> $SMTP_SERVERS 25 (msg:"MALWARE-OTHER
            UTF-8 BOM in zip file attachment detected";
            flow:to_server,established; content:".zip"; fast_pattern:only;
            content:"Content-Disposition: attachment|3B|"; content:"filename=";
            nocase; pcre:"/filename=[^\n]*?\x2ezip[\x22\x27\s]/si"; file_data;
            content:"|EF BB BF 50 B4|"; depth:5; metadata:policy balanced-ips
            drop, policy security-ips drop, ruleset community, service smtp;
            
reference:url,http://blogs.mcafee.com/mcafee-labs/phishing-threat-uses-utf-8-bom-in-zip-signature-to-evade-detection;
            classtype:trojan-activity;)

            alert tcp $EXTERNAL_NET [110,143] -> $HOME_NET any
            (msg:"MALWARE-OTHER UTF-8 BOM in zip file attachment detected";
            flow:to_client,established; content:".zip"; fast_pattern:only;
            content:"Content-Disposition: attachment|3B|"; content:"filename=";
            nocase; pcre:"/filename=[^\n]*?\x2ezip[\x22\x27\s]/si"; file_data;
            content:"|EF BB BF 50 B4|"; depth:5; metadata:policy balanced-ips
            drop, policy security-ips drop, ruleset community, service imap,
            service pop3;
            
reference:url,http://blogs.mcafee.com/mcafee-labs/phishing-threat-uses-utf-8-bom-in-zip-signature-to-evade-detection;
            classtype:trojan-activity;)

            alert tcp $EXTERNAL_NET $HTTP_PORTS -> $HOME_NET any
            (msg:"MALWARE-OTHER UTF-8 BOM in zip file attachment detected";
            flow:to_client,established; content:".zip"; fast_pattern:only;
            http_header; content:"filename="; nocase; http_header;
            pcre:"/filename=[^\n]*?\x2ezip[\x22\x27\s]/si"; file_data;
            content:"|EF BB BF 50 B4|"; depth:5; metadata:policy balanced-ips
            drop, policy security-ips drop, ruleset community, service http;
            
reference:url,http://blogs.mcafee.com/mcafee-labs/phishing-threat-uses-utf-8-bom-in-zip-signature-to-evade-detection;
            classtype:trojan-activity;)

      Dammit Joel...you're always look so much better than mine :P  As always, thanks a bunch :)

:D

Alright, I have these in the test system, let's see how they do.

--
Joel Esler
Senior Research Engineer, VRT
OpenSource Community Manager
Sourcefire

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