Adobe releases first set of patches for cross-site scripting vulnerability

Adobe late Tuesday released the first set of security patches to address the cross-site scripting vulnerability disclosed by European researchers late last year. The flaw allows Acrobat Reader v.7.0.8 and earlier versions to be exploited by hackers.

Left unpatched, the vulnerable versions of Adobe’s Reader, Acrobat Standard, Acrobat Professional and Acrobat 3D let an attacker easily include JavaScript code in a browser session so that when a user clicks on a malicious link to a PDF on the Web, the attack code is activated. There is no vulnerability associated with PDF itself.

The latest version of Acrobat, v.8., released in December, isn’t vulnerable to the cross-site scripting attack. But because researchers Stefano Di Paola and Giorgio Fedon drew attention to the flaw when they presented a paper at a Berlin conference in late December, Adobe has been working to address the problem.

“Adobe strongly urges Adobe Reader users update to the latest version, Reader 8. Adobe Reader 7 users who wish to stay with their current version can follow the instructions outlined in the bulletin,” Adobe advised last night. Adobe also issued recommendations for a server-side workaround for Web site operators.

Adobe labels the cross-site scripting flaw critical, and many security experts say it’s one of the worst security problems they've ever seen given that Adobe Reader is so widely used for viewing PDF files.

“It’s the prevalence of it,” notes Amol Sarwate, manager of vulnerability research at security services firm Qualys. “There’s an Adobe Reader installed on almost every desktop.”

“This is so very dangerous because it exploits a random PDF on the Web,” says Billy Hoffman, leading researcher at vulnerability-assessment firm SPI Dynamics. “I send someone, the victim, a link to a legitimate Web site. The vulnerability allows you to put JavaScript in it, executing in the client’s browser. Then, I can simulate the victim at that time. You're piggybacking perfectly legitimate commands on top of PDF.”

“This is the biggest issue in security I’ve ever seen,” says Danny Allan, director of strategic research at Web application security firm Watchfire. “It’s extremely easy for someone to do this. There’s nothing difficult here.”

Spam-filtering appliance vendor Barracuda Networks says it has updated its equipment to filter out spam with a URL link containing JavaScript for a PDF. “There’s no reason a URL to a PDF file should contain a JavaScript for a PDF,” says Steve Pao, vice president of product development at Barracuda.

An Adobe spokesman says Adobe expects to soon post additional security patches for the cross-site scripting vulnerability for Adobe Reader 6 users.

Read more about security in Network World's Security section.