Adobe fails to fully fix PDF bug

Plugs only part of the hole disclosed in March, may return for a second try at patching

An Adobe patch for a well-publicized bug in the company's Reader PDF software doesn't fix the vulnerability, the security researcher who uncovered the flaw confirmed.

Last Tuesday, Adobe shipped an update for Reader and Acrobat, its popular PDF viewing and creation programs, that patched 17 vulnerabilities, including a design issue that gave attackers an easy way to con users into running malware. The bug, which was disclosed by Belgium researcher Didier Stevens in late March, allowed hackers to leverage the "/Launch" function, a feature that executes other software from within a PDF document.

When combined with another trick -- Stevens also showed how a Reader warning could be changed to further fool users -- the flaw could be used to dupe users into launching malware masquerading as legitimate software.

Hackers have been using Stevens' technique in mass attacks to infect Windows PCs since mid-April.

On Sunday, Stevens confirmed that the patch didn't fix the flaw.

"I did some research and discovered that Adobe implemented a blacklist of extensions for the launch action, but that the blacklisting functionality identifies the file type of 'cmd.exe' as .exe', and not .exe," he said in a post to his blog July 4.

Attackers can still get a PDF document to run malware simply by enclosing the malicious filename within single- or double-quotation marks, Stevens said.

Le Mahn Tung , a researcher at Bach Khoa Internetwork Security (BKIS), which is housed at the Hanoi University of Technology in Vietnam, first noticed that Adobe had not properly patched the bug.

On his blog, Stevens offered a workaround to deflect attacks that sidestep Adobe's blacklist. His workaround, however, involves editing the Windows registry, a task most users will shy away from.

Adobe admitted its blacklist wasn't foolproof, and said it was looking into Tung's and Stevens' bypass techniques.

"While blacklist capabilities alone are not a perfect solution to defend against those with malicious intent, this option reduces the risk of attack," said Brad Arkin, Adobe's director of security and privacy, in an entry on the company's security team's blog . "We will evaluate [the Tung] workaround to determine whether additional changes to the blacklist are required."

Adobe fixed the warning dialog flaw, Stevens noted, so that hackers could not modify it to increase the chance that users would fall for their ploys. Adobe's Arkin also pointed that out. "The warning message provided includes strong wording advising users to only open and execute the file if it comes from a trusted source," Arkin said.

Last week's patch also modified Reader and Acrobat so that the /Launch feature is disabled by default, requiring users who want the functionality to manually switch it on. In earlier editions, /Launch was enabled by default.

The updated Reader and Acrobat for Windows, Mac and Linux can be downloaded using the links included in the security advisory Adobe published last week. Alternately, users can run the programs' built-in update mechanism to grab the new versions.

Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at @gkeizer

Join the Good Gear Guide newsletter!

Error: Please check your email address.
Rocket to Success - Your 10 Tips for Smarter ERP System Selection

Tags securityadobepdf bug

Keep up with the latest tech news, reviews and previews by subscribing to the Good Gear Guide newsletter.

Gregg Keizer

Computerworld (US)
Show Comments

Most Popular Reviews

Latest Articles

Resources

PCW Evaluation Team

Matthew Stivala

HP OfficeJet 250 Mobile Printer

The HP OfficeJet 250 Mobile Printer is a great device that fits perfectly into my fast paced and mobile lifestyle. My first impression of the printer itself was how incredibly compact and sleek the device was.

Armand Abogado

HP OfficeJet 250 Mobile Printer

Wireless printing from my iPhone was also a handy feature, the whole experience was quick and seamless with no setup requirements - accessed through the default iOS printing menu options.

Azadeh Williams

HP OfficeJet Pro 8730

A smarter way to print for busy small business owners, combining speedy printing with scanning and copying, making it easier to produce high quality documents and images at a touch of a button.

Andrew Grant

HP OfficeJet Pro 8730

I've had a multifunction printer in the office going on 10 years now. It was a neat bit of kit back in the day -- print, copy, scan, fax -- when printing over WiFi felt a bit like magic. It’s seen better days though and an upgrade’s well overdue. This HP OfficeJet Pro 8730 looks like it ticks all the same boxes: print, copy, scan, and fax. (Really? Does anyone fax anything any more? I guess it's good to know the facility’s there, just in case.) Printing over WiFi is more-or- less standard these days.

Ed Dawson

HP OfficeJet Pro 8730

As a freelance writer who is always on the go, I like my technology to be both efficient and effective so I can do my job well. The HP OfficeJet Pro 8730 Inkjet Printer ticks all the boxes in terms of form factor, performance and user interface.

Michael Hargreaves

Windows 10 for Business / Dell XPS 13

I’d happily recommend this touchscreen laptop and Windows 10 as a great way to get serious work done at a desk or on the road.

Featured Content

Latest Jobs

Don’t have an account? Sign up here

Don't have an account? Sign up now

Forgot password?