Yahoo Messenger hit with ninth zero-day exploit

Attack code that targets Yahoo Messenger has been published on the Internet, a security researcher warned Wednesday, marking the ninth exploit aimed at the popular instant messaging software so far this year.

In a posting to the milw0rm.com Web site, someone identified as "shinnai" disclosed malicious Visual Basic code that allegedly lets attackers feed any file to users of the latest version of Messenger. The exploit code successfully executes on a fully-patched PC running Windows XP SP2, shinnai said, although the effect depends on the security settings of Internet Explorer (IE).

According to an e-mail alert from nCircle Network Security, hackers armed with the exploit could force-feed malware such as a Trojan horse to vulnerable users. It was nCircle that pegged the latest zero-day threat against Messenger as No. 9 for the year.

IE's security, however, can mitigate an attack. Users running the newer IE 7 with default security settings will probably be protected.

"This latest exploit is another data point in the strong trend toward IM client attacks," said Andrew Storms, nCircle's director of security operations. "IM vendors jockeying for market share are trying to lure new users with new features that also open up new risks to end users."

Storms was referring to the rash of instant messaging program flaws that have been uncovered in recent months. Yahoo Messenger, for example, has been patched several times this summer, while Microsoft decided less than a week ago on a mandatory upgrade that meant all users of its MSN Messenger and Windows Live Messenger clients had to update or lose access to the service.

Storms recommended that corporate IT admit that unauthorized instant messaging software is being used on their networks. "Enterprise IT teams that have been ignoring IM clients because they are not part of the 'official' infrastructure would be well advised to take steps to bring an IM client onto their supported platform and make sure their antivirus and spyware vendors work with their selected client," he said in an e-mail.

Yahoo, which patched Messenger twice last month, did not immediately respond to a request for confirmation of the newest flaw and queries about a patch timeline.