Once Again Cutwail Spam Campaign Ends Up In Phoenix Exploit Kit

In the past few months, a certain cybercrime group operates a large stable malware infrastructure, which started with a massive Wordpress-based compromise and keep harming since then by similar Web attacks. A few days ago we noticed another spike driven by Cutwail botnet.

Cutwail - Spam campaign

A massive spam email was sent to (notice the poor English in the email), manipulating the user into clicking the malicious URL. The URL leads the user to a malicious HTML page hosted on a compromised Web site with the following HTML file:

Obfuscated injected Javascript code

The obfuscated code above extracted to the following code:

De-obfuscated code

Eventually, the hidden IFRAME leads to the Phoenix Exploit Kit, which we analyzed in the previous attack driven by this cybercrime group. The reason why these spam emails don't refer the user directly to the Exploit Kit is the high frequency the domain is changed to avoid URL filtering, while the compromised Web site doesn't change. Moreover they specifically don't inject the malicious IFRAME into the homepage of that compromised site, so the site owner won't suspect that his account is being abused.

This specific attack can be easily identified by the following file names:

"index-include.htm"
"include-index.htm"

Besides the malicious HTML page, each compromised accounts contains the following files:

"title.php" – A standard PHP shell that can be downloaded from exploit-db.com

"edw.php" – A short script from the cybercriminals that helps the core server update the HTML page easily by uploading a new obfuscated JavaScript. Its code leads to a new domain. Following part of the PHP source code of this file:

Snippet PHP code of the hidden backdoor

Web site owners, ensure your hosting account doesn't contain a file with the name "edw.php".

All Trustwave M86 Secure Web Gateway customers are protected against this attack by default. The access to the exploit page is blocked.

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