The flaw, which was reported Thursday by security researcher Aviv Raff, has to do with the way that Skype makes use of a Windows Internet Explorer component to render HTML. Because Skype does not apply strict security controls to the software, an attacker could run scripting code on the victim's system in a dangerous fashion and ultimately install malicious software.
The problem is that Skype runs the IE component with the less locked-down "Local Zone" security setting. Because of this attackers are able to do "all sorts of things... [such as] reading/writing files from the local disc and launching executables," wrote security researcher Petko Petkov, in a Thursday blog post about the issue.
For an attack to work, the bad guys would first need to find a trustworthy Web site that contained a common programming flaw called a cross-zone scripting error. This bug would give them a way to trick Skype into running their malicious script as if it came from a trusted Web site.
In a video posted to his blog, Raff showed how a cross-zone scripting flaw on the Dailymotion.com Web site could be exploited to launch the calculator program in Windows, using Skype's "Add video to chat" feature.
"The user simply needs to visit DailyMotion via Skype's 'Add video to chat' button and stumble upon a move which contains the cross-site scripting vector," Petkov wrote.
Worse, attackers could flood the site with maliciously encoded advertisements in order to boost their likelihood of infecting a victim, he said. "This type of attack is very easy to pull and it requires almost zero preparation."
The flaw affects the latest version of Skype -- version 126.96.36.199 -- Raff said. Older versions of the software may also be at risk. "Until the Skype guys fix this vulnerability, I recommend that you stop searching for videos in Skype," he wrote.
Skype representatives could not be reached immediately for comment.