PDF security hole opens can of worms

The security perils of PDF files have been further highlighted by new research illustrating how a manipulated file might be used to infect other PDF files on a system.

Jeremy Conway, an application security researcher at NitroSecurity, said the attack scenario he has discovered shows PDFs are "wormable". Computer viruses are capable, by definition, of overwriting other files to spread. Conway's research is chiefly notable for illustrating how a benign PDF file might become infected using features supported by PDF specification, not a software vulnerability as such, and without the use of external binaries or JavaScript.

The "wormable PDF" research comes days after another security researcher, Didier Stevens, showed how it was possible to both embed malicious executables in PDFs and manipulate pop-up dialog boxes to trick victims into running a malicious payload. Both Adobe and FoxIT are working on a fix against the security shortcomings in their respective PDF viewing packages illustrated by the research.

Conway, who last week published an advisory and proof of concept video demo on wormable PDFs, said he was inspired to hunt for related vulnerabilities in the PDF specification by Stevens' research. A fix capable of blocking the security loophole discovered by Stevens ought to also prevent the possibility of 'worming' PDFs. "If the vendors figure out a method to prevent Didier’s example this same fix will stop this proof of concept as well," Conway writes.

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