CyanogenMod developers remove code that logged device screen-lock patterns

The development team of CyanogenMod, a popular community-built Android firmware, discovered and removed a line of code that posed potential security risks because it logged and stored device screen-lock patterns in a file.

The unwanted line of code was added back in August in CyanogenMod version 10, which is based on Android 4.1 (Jelly Bean), as part of a new feature that allowed the size of the lock screen’s dot grid to be configurable — for example from the default 3×3 size to 6×6.

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“The line of code has been introduced by a respectable member of the Cyanogen community and I don’t suspect it has been added with malicious intent,” Bogdan Botezatu, a senior e-threat analyst at antivirus vendor Bitdefender, said Tuesday via email. “Most probably, it is a snippet of code used during debugging and forgotten when committing the code.”

However, the presence of the code does pose some security risks, Botezatu said. For example, if a locked device is lost or stolen and that device is rooted, which is the case for many CyanogenMod devices, the log file containing its unlock swipe pattern can easily be read by connecting the device to a computer and using the ADB (Android Debug Bridge) command line tool.

A jealous spouse could also use this simple method to learn the screen unlock pattern for their partner’s phone and later snoop on their phone call history, emails, private social networking chats, etcetera, Botezatu said. “GPS tracking or keylogging applications can also be installed while the phone is unlocked.”

This case is the best example of how a simple line of forgotten code can cause a chain reaction that results in the theft of personal information or invasion of privacy, Botezatu said.

The problematic line of code was spotted and removed by CyanogenMod developer Gabriel Castro on Sunday. “I’m really surprised nobody caught this,” he wrote in his patch comments.

Users of CyanogenMod 10 who are concerned about this bug affecting their privacy or security should upgrade to the latest nightly build available for their device model.

According to statistics, the official builds of CyanogenMod are installed on 1,137,335 devices and unofficial builds on 1,366,560 devices. The nightly builds of CyanogenMod 10 are currently the most popular versions of CyanogenMod and account for over 240,000 official installs.