Hackers exploit new PDF zero-day bug, warns Adobe

Criminals conduct 'limited' attacks with rigged PDF attachments

Adobe today warned users that attacks have begun exploiting an unpatched bug in its popular Reader and Acrobat PDF viewing and creation software.

The company issued an advisory on short notice today, saying that it had learned of in-the-wild attacks only on Tuesday.

"A critical vulnerability exists in Adobe Reader 9.3.4 and earlier versions for Windows, Macintosh and UNIX, and Adobe Acrobat 9.3.4 and earlier versions for Windows and Macintosh," Adobe's warning read. This vulnerability could cause a crash and potentially allow an attacker to take control of the affected system.

"Adobe is in the process of evaluating the schedule for an update to resolve this vulnerability," the advisory added.

Other than to say that "at this point, [attacks] appear to be limited," Adobe offered little information on the bug today.

But Mila Parkour, the independent security researcher who reported the bug to Adobe on Tuesday, had plenty in a post to her Contagio Malware Dump blog.

Parkour uncovered a malicious e-mail message with a rogue PDF attachment that urged recipients to open the document. "Want to improve your score? In these golf tips, David Leadbetter shows you some important principles," the message read.

Leadbetter, a well-known golf coach and author on the game, operates more than two dozen golf academies in 13 countries, and claims the title of "master of the art of teaching the golf swing."

Symantec pegged the threat with a score of 8.5 out of possible 10, while Danish vulnerability tracker Secunia rated the vulnerability as "Extremely critical," its highest-possible threat level.

According to a Symantec, the bug is in Reader's and Acrobat's parsing of PDF files that contain malformed TIFF image files. Specifically, said the company in an alert to customers, "the issue occurs due to a heap-memory corruption issue in 'cooltype.dll.'"

CoolType is an Adobe font-rendering technology, similar to Microsoft's ClearType.

Adobe did not spell out a timetable for patching the Reader/Acrobat zero-day vulnerability, nor did it offer users any ad hoc defensive measures they could employ until a fix is ready.

The next regularly-scheduled patch date for Reader and Acrobat is Oct. 13, but Adobe has been known to issue so-called "out-of-band" emergency updates when active attacks spike.

An Adobe spokeswoman hinted that the latter could easily occur. "With exploit code publicly available, [the current limited-only attack] could change," she said, talking about the exploit that Parkour has posted online.

Parkour has not released the exploit publicly, however, but has password-protected the malicious PDF she discovered, and will release it only to people who e-mail her.

Symantec urged Reader and Acrobat users not to open PDFs from untrusted or unknown senders.

Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at @gkeizer or subscribe to Gregg's RSS feed . His e-mail address is gkeizer@ix.netcom.com.

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