Proof-of-concept exploit available for Android app signature check vulnerability

Technical details about a vulnerability allowing rogue modifications of legitimate Android apps were publicly disclosed

Technical details and a proof-of-concept exploit have been published for a recently announced Android vulnerability that potentially affects millions of devices and allows attackers to turn legitimate apps into Trojan programs.

Last Wednesday security researchers from mobile security firm Bluebox Security announced that a vulnerability exists in the way Android verifies the digital signatures of application packages (APKs), allowing attackers to modify them without breaking their digital signatures.

The Bluebox researchers only provided a high-level description of the bug and its potential impact, keeping the technical details for an upcoming presentation at the Black Hat security conference in Las Vegas.

Since then, developers of CyanogenMod, a community-built Android firmware version, have identified where the bug is located and even merged a patch from Google into their code.

Using the information from the public CyanogenMod bug entry, Pau Oliva Fora, a mobile security engineer at security firm ViaForensics, developed a proof-of-concept Linux shell script that can be used to modify an app in a way that exploits the flaw. The code makes use of the APKTool program and was released Monday on Github.

"It's a problem in the way Android handles APKs that have duplicate file names inside," Oliva Fora said Tuesday via email. "The entry which is verified for signature is the second one inside the APK, and the entry which ends up being installed is the first one inside the APK -- the injected one that can contain the malicious payload and is not checked for signature at all."

The Bluebox researchers said last week that Google made changes to Google Play in order to detect apps modified in this way and that a patch has already been shared with device manufacturers. This only leaves users who install applications from sources other than Google Play -- a process known as sideloading -- potentially vulnerable.

"I think it's a very serious vulnerability, and everyone with an unpatched device should be cautious about what they install, especially if it doesn't come from an official distribution channel," Oliva Fora said.

The vulnerability presents benefits for Android malware authors because it allows them to add malicious code to legitimate app packages and have them properly update the original applications if they are installed on the targeted devices, the researcher said.

Android malware authors are already distributing malicious apps that masquerade as popular games or applications though a variety of methods, including through third-party app stores. This vulnerability could make this social engineering technique more efficient.

Fortunately, APKs modified in this way should be very easy to detect by antivirus vendors, Oliva Fora said. "They just have to look for duplicate file names inside an APK file."

It would have been better if technical details about the vulnerability had not been disclosed until Black Hat, as Bluebox Security originally intended, the researcher said. However, "I'm sure that Jeff Forristal's [the Bluebox CTO] Black Hat talk will not disappoint, even if the details of the vulnerability are known," he said.

"A coordinated disclosure usually makes sure most users are safe when the details of the vulnerability are disclosed, but due to the nature of the Android ecosystem, vendors and carriers will not deploy a patch for abandoned devices and sadly many devices will remain vulnerable forever," Oliva Fora said.

Join the PC World newsletter!

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

Tags viaForensicsBluebox SecurityAndroid OSsecuritymobile securitymobileExploits / vulnerabilitiesmalwaremobile applications

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

Lucian Constantin

IDG News Service
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?