Acrobat Reader flaw opens websites to XSS attacks

Security experts warned Wednesday of a vulnerability in Adobe Acrobat Reader plug-in that makes PDF-friendly websites susceptible to cross-site scripting (XSS) attacks, worms, and theft of cookies and session information. Initially disclosed by two security researchers, Stefano Di Paola and Giorgio Fedon, at the 23rd Chaos Communication Congress in Berlin last week, the vulnerability occurs in the Open Parameters feature in Adobe Acrobat Reader. The function gives web developers the ability to pass parameters when a user opens a PDF file, but it also opens up the ability to execute JavaScript code on the client side, warned researcher Hon Lau on a Symantec blog.

"All the attacker has to do is find out who is hosting a PDF file on their web server and then piggyback on it to mount an attack," he said. "What this means in a nutshell is that anybody hosting a PDF, including well-trusted brands and names on the web, could have their trust abused and become unwilling partners in crime."

Researchers with Secunia rated the threat as "less critical" and recommended upgrading to Acrobat Reader 8.0 to fix the problem, but other experts said the threat is more pressing.

Researchers at Symantec and VeriSign iDefense warned that the vulnerability poses considerable risk because of widespread use of PDF browser plug-ins within most web sites.