The monthly Android security update released this week fixes the serious Dirty COW privilege escalation attack that can allow malicious apps to take full control of devices.
Dirty COW (copy-on-write) is a privilege escalation vulnerability that has existed in the Linux kernel for the past nine years and is already being exploited in the wild. It affects Android because the mobile OS is based on Linux, but it was initially believed that the SELinux security policies enforced by default in Android provided some mitigation against the attack.
That's not necessarily the case, according to security researchers from Trend Micro, who devised a new Dirty COW attack variant that bypasses SELinux restrictions by injecting malicious code directly into other processes.
"Our proof of concept patches libbinder.so to give our app system/root privileges," the Trend Micro researchers said Tuesday in a blog post. "We used this ability to bypass Android’s permission security model to steal information and control system functions."
Google developed a patch for Dirty COW last month and shared it with device manufacturers. However, it didn't include it in its firmware updates for Nexus and Pixel devices at the time and didn't make its inclusion mandatory for manufacturers either, until this month.
This month's security update also fixes an interesting security vulnerability in the mechanism that downloads GPS satellite information, known as the GPS almanac.
Researchers from security consultancy Nightwatch Cybersecurity have found that some Android devices with Qualcomm chipsets download this GPS information file from Internet servers without authentication, encryption or file signature verification. This means that an attacker in a position to intercept the download requests from Android phones can serve bogus GPS assistance files to the devices.
Google has rated this vulnerability as high severity, because it can result in a denial-of-service attack that delays the phone's GPS receiver from establishing a GPS lock.
According to the Nightwatch researchers, Qualcomm has known about the GPS almanac issue since 2014 and has advised its OEM customers to download the GPS assistance files over HTTPS or to switch to their latest format which includes a digital signature.
The December Android security update also includes patches for critical vulnerabilities in the kernel memory subsystem, NVIDIA GPU driver, NVIDIA video driver, kernel ION driver and various Qualcomm components.