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Security Research

Fake Flash Update With A Twist

June 22, 2012 - 2 min read
We've seen Fake Flash updates for several years. A webpage claims that the user is running an outdated of version of Flash and they require an upgrade of the plugin to watch a video. The fake Flash update is actually a malicious executable.

This type of attack is still going on. Today, I was investigating such a malicious page. The page claims to be from, a free porn site. The fake video player shows a warning: "You need the latest version of Adobe Flash Player to play this video."
Fake porn video
However, instead of downloading a malicious executable, the user is actually asked to download a fake Flash extension. There are different variants for different browsers: .XPI for Firefox, .CRX for Google Chrome, and .EXE (BHO + installer) for Internet Explorer.
Malicious extension for Firefox
Extension installation on Firefox
Fake extension installed

Browser extensions are open doors to infect users. Antivirus vendors do a very poor job at decting fake extensions, mostly because they are just plain text files (HTML, JavaScript), and cannot therefore contain binary malware. The VirusTotal reports for this particular attack illustrate the challenge:
  • executable (Internet Explorer): detection by 21/42 AV
  • XPI (Firefox): 0 detected!
  • CRX (Chrome): 0 detected!

Browser extensions

Browser extensions have a fairly simple structure. They don't generally contain any malicious code directly, rather, when the browser starts, the add-on fetches the malicious JavaScript code from an external server and executes it.
Fake extension code after deobfuscation

The current files being pulled are not very dangerous, but that could change in the future. An invisible IFRAME is inserted in each new page loaded. The IFRAME contains advertising from, and contains a username in the URL. This tells me that the adware author gets money for the traffic sent to this site, even if the infected user cannot actually see what is being loaded.
Remote file content after deobfuscation 

The author could change the remote file at any moment to do much more harm, like stealing cookies to obtain access to the user accounts on any site, stealing username/credentials being entered or previously saved, etc.
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