"All it takes is to open a [maliciously rigged] PDF document or stumble across a page which embeds one," said researcher Petko D. Petkov, aka pdp, in a blog posting on Sept. 20.
Petkov said he's closing the season with this highly critical flaw—a season that's included, at least in the past two weeks, his discovery of a slew of serious vulnerabilities in meta media files: a
Paul Henry, vice president of technology and evangelism at Secure Computing, based in San Jose, Calif., said in an interview with eWEEK that PDF vulnerabilities have a strong advantage when it comes to users being tempted into opening them, giving this vulnerability the potential to become a "huge" attack vector. "From a social engineering standpoint, it's easier to attach a PDF to e-mail and assume [the target will] open it. If you've got a request to launch a video conversation from someone you never heard of, chances are you won't do it. Or you won't click on a video online if you don't know where it's from. But from a social engineering point of view, this is deeper."
For its part, Symantec, based in Cupertino, Calif., on Sept. 20 warned customers using its DeepSight Alert Services that Adobe Acrobat is subject to "an unspecified vulnerability when handling malicious PDF files," allowing remote users to take over targeted machines.
The scenario is that an attacker rigs a PDF file designed to exploit the flaw. He or she distributes it via e-mail or through other means, or hosts it on a Web page. When a user opens the rigged PDF file with a vulnerable application, the user's machine can be loaded with malware that makes it open to a takeover.
Symantec said it's not aware of any working exploits out yet.
Still, Henry warned, the PDF threat is real. "The ability to use PDFs to install malware and steal personal information from remote PCs is here," he said in a statement. "Readers should be cautioned to only open PDF files from senders they explicitly trust."
Given that this latest meta media file flaw with PDF documents is so critical, given also that PDFs are used throughout the business world, and given the fact that he expects Adobe will take a while to fix its closed-source product, Petkov said he's refraining from publishing any POC (proof-of-concept) code.
"You have to take my word for it. The POCs will be released when an update is available," he said.
This has miffed some. "If you have nothing else to publish than 'Please don't open PDF Docs, but I can't tell you why,' it would be a better choice [to] shut up instead [of] bringing no information," wrote somebody with the handle of Jan Heisterkamp.
Others are willing to take Petkov's word that the flaw is too critical for a POC. As it is, Petkov's credibility is shored up in no small part by five PDF POCs he put out in January.
One of those PDF vulnerability POCs automatically opened a folder displaying the victim's c: drive on his desktop; another displayed the file path to the temporary stored PDF and revealed the user name; and Petkov also posted self-contained, local, Universal PDF XSS (cross-site scripting) flaws: one for Internet Explorer, one for Firefox and one for Opera.
In spite of Petkov's having refrained from putting out a POC for the latest PDF flaw, somebody's sure to piece together an exploit or POC out of the other five, Henry said.
"Everybody and his brother has the other five POCs he put together. With a little tweaking I'm sure they'll put them together pretty quickly," he said. "I would have to assume [the six PDF vulnerabilities are related]. He's done a lot of work attaching JavaScript to media files. We have to assume this latest trick involves a change in something with the media files, with JavaScript. It's not rocket science."
Henry said Secure Computing, for one, has been sounding the alarm about PDF since Petkov's original postings.
"We raised the flag in January when [Petkov] discovered the initial [PDF] vulnerabilities and publicly released the POC code," he said. "Shortly after that we saw a huge upsurge in PDF attachments in spam. We all have to be cognizant that the POC is out there for potential vulnerabilities. This would be a very good vehicle for malicious guys to move code into our networks."
Adobe, also based in San Jose, said within the past few weeks that the five vulnerabilities in the January POCs represented a low threat risk. But with Petkov's most recent finding, Henry said, "We see an announcement that at least this current version is absolutely not low risk."
"I think this will create problems for us," Henry said. "I'm [warning] people … plans need to be put in place to quickly raise awareness in the organization that there might be a risk in PDF files. We're informing users to not open files that a) come from someone they don't know and b) they aren't expecting."
Petkov wrapped up his most recent, most terse PDF posting by telling Adobe's representatives that they can contact him "from the usual place."
Adobe issued a statement on the evening of Sept. 20 saying that it's aware of Petkov's post, has been in communication with him and is researching the potential issue. Adobe will update users on its Adobe Security Bulletins and Advisories page. Also, the statement said, all documented security vulnerabilities and their solutions are distributed through the Adobe security notification service.
Petkov's advice is to keep away from PDF files, local or remote. He said other viewers besides Adobe's Acrobat Reader might be vulnerable as well. He has verified the PDF issue on Windows XP Service Pack 2 with the latest Adobe Reader 8.1, although previous versions are also affected, he said.
September 20, 2007
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