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Tweeted twitter.com/#!/StackSecurity/status/182748172869828608
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Multiple extension vulnerability. Is this malicious file triggered during form preview or after it has been uploaded?

I'm looking at one of our compromised web server logs and we found that an attacker has uploaded a file with multiple extension. Below is the IIS log. The log format are as below. I have removed the cookies and user agent values as they are a bit long and irrelevant.

#Fields: date time cs-uri-stem cs-uri-query c-ip cs-version cs(User-Agent) cs(Cookie) cs(Referer) sc-status sc-substatus sc-bytes time-taken 

One of line, we found this log

2012-03-09 02:49:16 /preview.asp path=./submit/file_20120222_ext_20120309_1049.asp;_20120309_1049.jpg&width=300|17|80040035|Not_a_JPEG_file:_starts_with_0x3c_0x25 xxx.xxx.xxx.xxx HTTP/1.1 - - http://xxx.xxx.xxx.xxx/mail.asp?err=2 500 0 471 203

then on the following line, we found the following log

2012-03-09 02:51:03 /submit/fle_20120222_ext_20120309_1049.asp;_20120309_1049.jpg - xxx.xxx.xxx.xxx - - - 403 1 1918 0

Does anyone have any idea if the malicious file is triggered in line 1 of the log or line 2 of the log?