The majority of devices running Google's Android operating system are susceptible to hacks that allow malicious apps to bypass a key security sandbox so they can steal user credentials, read e-mail, and access payment histories and other sensitive data, researchers have warned.

The high-impact vulnerability has existed in Android since the release of version 2.1 in early 2010, researchers from Bluebox Security said. They dubbed the bug Fake ID, because, like a fraudulent driver's license an underage person might use to sneak into a bar, it grants malicious apps special access to Android resources that are typically off-limits. Google developers have introduced changes that limit some of the damage that malicious apps can do in Android 4.4, but the underlying bug remains unpatched, even in the Android L preview.

The Fake ID vulnerability stems from the failure of Android to verify the validity of cryptographic certificates that accompany each app installed on a device. The OS relies on the credentials when allocating special privileges that allow a handful of apps to bypass Android sandboxing. Under normal conditions, the sandbox prevents programs from accessing data belonging to other apps or to sensitive parts of the OS. Select apps, however, are permitted to break out of the sandbox. Adobe Flash in all but version 4.4, for instance, is permitted to act as a plugin for any other app installed on the phone, presumably to allow it to add animation and graphics support. Similarly, Google Wallet is permitted to access Near Field Communication hardware that processes payment information.

According to Jeff Forristal, CTO of Bluebox Security, Android fails to verify the chain of certificates used to certify an app belongs to this elite class of super privileged programs. As a result, a maliciously developed app can include an invalid certificate claiming it's Flash, Wallet, or any other app hard coded into Android. The OS, in turn, will give the rogue app the same special privileges assigned to the legitimate app without ever taking the time to detect the certificate forgery.

"All it really takes is for an end user to choose to install this fake app, and it's pretty much game over," Forristal told Ars. "The Trojan horse payload will immediately escape the sandbox and start doing whatever evil things it feels like, for instance, stealing personal data."

Other apps that receive special Android privileges include device management extensions from a company known as 3LM. Organizations use such apps to add security enhancements and other special features to large fleets of phones. An app that masqueraded as one of these programs could gain almost unfettered administrative rights on phones that were configured to work with the manager. Forristal hasn't ruled out the existence of other apps that are automatically assigned heightened privileges from Android.

Changes introduced in Android 4.4 limit some of the privileges Android grants to Flash. Still, Forristal said the failure to verify the certificate chain is present in all Android devices since 2.1. That means malicious apps can bypass sandbox restrictions by impersonating Google Wallet, 3LM managers, and any other apps Android is hardcoded to favor. A spokesman for Google issued the following statement:

We appreciate Bluebox responsibly reporting this vulnerability to us; third-party research is one of the ways Android is made stronger for users. After receiving word of this vulnerability, we quickly issued a patch that was distributed to Android partners, as well as to AOSP. Google Play and Verify Apps have also been enhanced to protect users from this issue. At this time, we have scanned all applications submitted to Google Play as well as those Google has reviewed from outside of Google Play, and we have seen no evidence of attempted exploitation of this vulnerability.

The statement didn't say exactly what Google did to patch the vulnerability or specify if any Android partners have yet to distribute it to end users. This article will be updated if company representatives elaborate beyond the four sentences above.

As Ars has documented previously, it's not unusual for attackers to sneak malicious apps into the official Google Play marketplace. If it's possible for approved apps to contain cryptocurrency miners, remote access trojans, or other hidden functions, there's no obvious reason they can't include cryptographic credentials fraudulently certifying they were spawned by 3LM, Google, Microsoft, or any other developer granted special privileges.

"With this vulnerability, malware has a way to abuse any one of these hardcoded identities that Android implicitly trusts," said Forristal, who plans to divulge additional details at next week's Black Hat security conference. "So malware can use the fake Adobe ID and become a plugin to other apps. Malware can also use the 3LM to control the entire device."

Listing image courtesy of Greayweed.