By Lisa Vaas
September 20, 2007
A zero-day PDF vulnerability in Adobe's Acrobat Reader has come to light
that can lead to Windows boxes getting taken over completely and
invisibly, according to a security researcher.
"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 flawa
season that's included, at least in the past two weeks, his discovery of
a slew of serious vulnerabilities in meta media files: a QuickTime flaw
that can be used to hijack Firefox and Internet Explorer; a simple
method of loading HTML files into Windows Media Player files; and an
easy, six-step method by which to penetrate Second Life accounts with an
This PDF vulnerability is even worse than the QuickTime flaw, Petkov
said. Mozilla provided a Firefox workaround for the QuickTime flaw
earlier the week of Sept. 17, but it can still be used to compromise
Internet Explorer, as security researcher Thor Larholm demonstrated in a
posting on Sept. 19. Apple hasn't yet released any details on the status
of a QuickTime fix.
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
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].
assume this latest trick involves a change in something with the media
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
"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 representatives hadn't been able to provide information on
the company's awareness of, or response to, the vulnerability by the
time this story posted.
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.
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