Update: Skype plugs critical bug with temp move

Computerworld - Hackers can exploit newly uncovered vulnerabilities in Skype Ltd.'s popular chat and VoIP software to shanghai a Windows PC, security researchers said Thursday.

By Friday morning, Skype had confirmed one of the bugs, slapped the highest-possible vulnerability rating on it and temporarily disabled the feature used to exploit the flaw. However, it has not responded to a second, more serious charge that attackers could nail Skype users at public wireless hot spots.

Early on Thursday, noted Israeli researcher Aviv Raff had spelled out what he called a "cross-zone scripting vulnerability" in Skype that could be leveraged by attackers armed with malicious video files. The way in, Raff explained, was through a security door that Skype left wide open.

"Skype uses [Microsoft Corp.'s] Internet Explorer Web control to render internal and external HTML pages," Raff said in a posting to his blog early Thursday. "[But] Skype is running this Web control in Local Zone ... [and] the HTML pages in a not-locked Local Zone mode."

Translation: If an attacker manages to inject a malicious script into any of those HTML pages, he can completely compromise the machine.

In a demonstration, Raff posted a tricked-out video file to the Dailymotion video-sharing service that, when called using the software's Add Video to Chat feature, runs harmless arbitrary code. The exploit relied on a separate cross-site scripting vulnerability on Dailymotion, which is one of Skype's video partners.

Raff's innocuous demo, however, could be replaced by attack code of the hacker's choice. "An attacker can now upload a movie, set a kewl popular keyword (e.g. 'Paris Hilton') and own any user that will search for a video with those keywords through Skype," he noted.

Fellow researcher Petko Petkov, a U.K.-based penetration tester and one of the masterminds behind the GNUCITIZEN group, stressed how easy an attack would be to run. "The attack vector is a bit convoluted, but very much possible and quite practical," Petkov said on the GNUCITIZEN site. "The most obvious approaches would be to either social engineer the user or spam Dailymotion with hundreds of infected movies that correspond to popular keywords."

Early Friday, Skype posted a security advisory that acknowledged the cross-zone scripting bug, saying that it affected all Windows versions of the software, including 3.5 and the most-up-to-date 3.6. Skype also pegged the flaw as a "10" in the Common Vulnerability Scoring System, the highest rating allowed by the security industry's standard bug ranking system.

Skype does not yet have a patch in place, so instead, it simply shut off access to Dailymotion. "Skype has temporarily disabled users' ability to add videos from Dailymotion gallery until an official fix has been made available," the security bulletin said.