Maliciously crafted MKV video files can be used to crash Android phones

The announcement, by security researchers from Trend Micro, comes days after other Android media processing flaws were revealed. Those flaws could allow attackers to compromise devices with a simple MMS message.

The latest vulnerability is located in Android's mediaserver component, more specifically in how this service handles files that use the Matroska video container (MKV), the Trend Micro researchers said in a blog post Wednesday.

When the vulnerability is exploited, the device becomes silent and unresponsive. No ring tone or notification sounds can be heard and calls cannot be initiated or accepted. Furthermore, the user interface can become sluggish or completely unusable and, if the phone is locked, it cannot be unlocked, the researchers said.

The flaw can be exploited in two ways: through a malicious application that contains a malformed MKV file, or by browsing to a Web page with a specifically crafted MKV video embedded in it.

"The first technique can cause long-term effects to the device: An app with an embedded MKV file that registers itself to auto-start whenever the device boots would case the OS to crash every time it is turned on," the Trend Micro researchers said.

The effect of the Web-based exploit is not as persistent and the device can be rebooted to restore normal operation. However, the Web-based exploit works even if Chrome for Android is configured not to preload or autoplay video files, the researchers noted.

Trend Micro reported to flaw in May, it said, but Google assigned it a low priority.

One group of attackers who might abuse this sort of flaw are ransomware creators. Some existing ransomware apps attempt to prevent users from using their phones until they pay ransom fees.

This vulnerability could provide attackers with a way to achieve that same effect, but in a way that would make users more likely to pay up, the Trend Micro researchers said.

The flaw affects all phones running Android 4.3 (Jelly Bean) and higher, including the latest 5.1.1 (Lollipop) update. That's more than 50 percent of Android devices, according to the Google Play statistics for June.

No patch has been yet released to the Android Open Source Project (AOSP), the Trend Micro researchers said.

In an emailed statement, a Google representative said that the company hasn't seen any evidence of attempts to exploit this flaw so far, but is closely monitoring for such attacks.

"Should there be an actual exploit of this, the only risk to users is temporary disruption to media playback on their device," the representative said. "So, simply uninstalling the unresponsive application or not returning to a website that causes the browser to hang would correct the issue. In addition, we will provide a fix in a future version of Android."

Even when a patch will be provided to device manufacturers, it will probably take months for it to reach a significant number of devices. And many devices will likely never get patched because they're no longer supported by their manufacturers.

The slow distribution of security updates coupled with the version fragmentation is the Achilles heel of the Android ecosystem, according to many security researchers. All software has bugs, but a developer's ability to create and distribute patches quickly plays a critical role in limiting the impact of potential vulnerabilities.

Researchers expect to find more vulnerabilities in Android's multimedia processing components, especially because they're designed to parse input from untrusted sources.

Vulnerabilities often stem from applications behaving abnormally when receiving unexpected input, so programs that process files naturally have been more likely to have vulnerabilities. Media libraries and frameworks fall into this category because video and audio files are complex and take a lot of processing. They can have various metadata, encoding, formatting and containers, providing many opportunities for malformed input.

"Further research into Android -- especially the mediaserver service -- may find other vulnerabilities that could have more serious consequences to users, including remote code execution," the Trend Micro researchers said.

Joshua Drake, a security researcher who recently found critical vulnerabilities in Android's Stagefright multimedia framework, described the component's code as "not very mature" and its security flaws as "beginner-ish."