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Malware forces Firefox to save passwords

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Miscreants have developed a strain of malware that makes sure website passwords are recorded by a victim's browser.

Saving website logic credentials is a user controlled option in all browsers, often enabled by default. But the practice is frowned upon by security researchers, who point to the risk that passwords left in browsers might easily be extracted by password-stealing Trojans, such as Zeus.

Anti-virus analysts at Webroot recently discovered a malware trick that means that even if fans of Firefox avoid saving their login credentials, their passwords are still saved by the open source browser. The Trojan modifies a core Firefox file, called nsLoginManagerPrompter.js, which controls whether Firefox prompts a user to save passwords when he or she logs into a secure site.

"Before the infection, a default installation of Firefox 3.6.10 would prompt the user after the user clicks the Log In button on a Web page, asking whether he or she wants to save the password," Webroot researcher Andrew Brandt explains. "After the infection, the browser simply saves all login credentials locally, and doesn’t prompt the user."

Any time an item of malware gains admin rights to a compromised box it's game over, not least because at that point it's possible to download secondary malware that carries out malign functions not code into the primary infector. Nonetheless, changes in the tactics used by hackers are noteworthy, not least because they can screw up or complicate the disinfection process.

The keylogging Trojan also creates a new user account (username: Maestro) on the infected system and scrapes information from the registry, specifically the Protected Storage area used by IE to store passwords, and from Firefox’s own password storage, before trying to upload the stolen data to cybercrooks. The control server was taken offline between the time the malware first appeared and the point where analysis was completed, but a name was left in the code that pointed to the name of the likely perp and (in the best Web 2.0-stylee) the Facebook profile of an Iranian web user.

Webroot warns that some of the people who frequent the same underground hacker hangouts as Zeynali have applied his keylogger tool to their own nefarious ends. The security firm identifies the malware used in the attack as Trojan-PWS-Nslog.

A write-up on the attack by Webroot can be found here. ®

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