Adobe Reader may be subject to a security hole that creates a means for hackers to take over vulnerable Windows boxes simply by opening a maliciously constructed PDF document.

Gray hat hacker Petko Petkov, who first discovered the bug, omits details of the supposed flaw. He said security concerns over the potency of the flaw alongside concerns over the time it might take for Adobe to come up with a fix have prompted him to hold back from publishing proof of concept code.

By way of illustration, a video clip published by Petkov depicts how Windows calculator starts when a PDF document is opened. The same approach might be used to launch a malicious payload.

Petkov verified the bug on Windows XP SP2 with the latest Adobe Reader 8.1, 8.0 and 7. Previous versions - as well as other PDF viewers - might also be affected. Windows Vista users, however, are projected against the attack, according to Petkov.

Although the warning over the attacks lacks details it comes from a source who's built up a strong reputation for unearthing security bugs. Petkov previously discovered bugs in the Second Life client and (more recently) Firefox's QuickTime plugin, Heise Security reports.

Security observers are taking the threat seriously. "PDF vulnerabilities have the strong potential to become a huge attack vector based on the social engineering aspect alone (people simply accept PDF files)," according to Paul Henry of Secure Computing. "This, coupled with the fact that nearly all technology solutions on the market are severely lacking in the capability to open and scan PDFs in-depth for malicious code, creates huge risk potential."

Caution about opening PDF files from unknown sources or websites is sensible, even though Petkov’s claims remain unverified. ®

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