Feeds

Another zombie 'bogus app' bug shambles out of Android

KitKat is safe, older Androids susceptible to .ZIP-derived attack

Choosing a cloud hosting partner with confidence

Jay Freeman, aka @saurik, has detailed another Zip implementation bug in pre-4.4 (Kit Kat) versions of Android which, similarly to the notorious APK vulnerability exposed earlier this year, opens a hole that malware can sneak through.

Freeman – whose previous credentials include security analysis of Google Glass and uncovering the dodginess of the “iMessage for Android” app – has written in a blog post that he uncovered the extra vulnerability in June, but waited until Android 4.4 (with a fix) was shipping.

Freeman's dense post is here, and is unpicked and explained by Sophos' Paul Ducklin at Naked Security here.

In brief, the extra APK vulnerability offered a path for an attacker to exploit the way Android used Zip file headers to verify the software. As Ducklin explains, Zip still carries an obsolete of its history around with it: lots of filename redundancy in case files had to be split across multiple floppy (remember those?) disks. To help a program navigate a file, the header includes a field for filename length – this lets an extractor navigate to where the file data is, by skipping the header.

As Ducklin writes, the problem is this: “The Java code in Android 4.3 and earlier, that extracts the file data to verify it, uses the filename length from the central directory. But the C code that extracts the file to install and execute it uses the filename length in the local header.”

An attacker could then take a verified app, add their malware, and modify the header length the C-code loader uses to point not to the legitimate app, but to the malware. Ducklin's illustration shows this simply:

Paul Ducklin's illustration of the APK vulnerability

Image: Paul Ducklin, Naked Security

As Saurik writes: “The central directory includes a file offset for each local header, so that once the Java code has finished verifying a file, it can jump directly to the next one, thus avoiding the local header data that would cause it to skip forward incorrectly. The imposter data, squeezed between the legitimate file and the next local header, is simply ignored.”

The fix in Kit Kat is to force Java to look at the same data as the C-loader so that a discrepancy is identified. ®

Beginner's guide to SSL certificates

More from The Register

next story
Russian hackers exploit 'Sandworm' bug 'to spy on NATO, EU PCs'
Fix imminent from Microsoft for Vista, Server 2008, other stuff
FYI: OS X Yosemite's Spotlight tells Apple EVERYTHING you're looking for
It's on by default – didn't you read the small print?
Microsoft pulls another dodgy patch
Redmond makes a hash of hashing add-on
'LulzSec leader Aush0k' found to be naughty boy not worthy of jail
15 months home detention leaves egg on feds' faces as they grab for more power
Forget passwords, let's use SELFIES, says Obama's cyber tsar
Michael Daniel wants to kill passwords dead
Kill off SSL 3.0 NOW: HTTPS savaged by vicious POODLE
Pull it out ASAP, it is SWISS CHEESE
Facebook slurps 'paste sites' for STOLEN passwords, sprinkles on hash and salt
Zuck's ad empire DOESN'T see details in plain text. Phew!
prev story

Whitepapers

Forging a new future with identity relationship management
Learn about ForgeRock's next generation IRM platform and how it is designed to empower CEOS's and enterprises to engage with consumers.
Cloud and hybrid-cloud data protection for VMware
Learn how quick and easy it is to configure backups and perform restores for VMware environments.
Three 1TB solid state scorchers up for grabs
Big SSDs can be expensive but think big and think free because you could be the lucky winner of one of three 1TB Samsung SSD 840 EVO drives that we’re giving away worth over £300 apiece.
Reg Reader Research: SaaS based Email and Office Productivity Tools
Read this Reg reader report which provides advice and guidance for SMBs towards the use of SaaS based email and Office productivity tools.
Security for virtualized datacentres
Legacy security solutions are inefficient due to the architectural differences between physical and virtual environments.