Mutating javascript malware

[Humpty]

Hackers are using a new technique to infect desktop PCs via compromised websites, while avoiding antivirus detectors, according to the SANS Institute.

 

SANS' ISC (Internet Storm Center) said on Thursday it has come across the attack on a compromised website, where an iframe was used to deploy various pieces of malicious code via Javascript. Iframes allow content from one website to be embedded in another website.

 

This technique in itself isn't new, but researchers found that the server deploying the malicious Javascript was heavily modifying it - "obfuscating" it - so as to be undetectable by antivirus detectors, the ISC said. Moreover, the obfuscations were generated randomly and on the fly, according to ISC handler Bojan Zdrnja.

 

"What makes this new is that the hosting website generates this code dynamically," he wrote in an analysis.

 

"Every time you request this web page it will use completely random names for all variables and functions... changing variable and function names even causes the payload information to change."

 

The technique makes the script code in effect undetectable by common types of malware scanners, Zdrnja said.

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