"It is very, very easy for malware to use this attack -- it is silent, transparent, with no notifications to users," Forristal said. The malicious app doesn't need any special permissions. It just needs to contain WebView code inside of it, which it can actually download after installation, he said.
Abusing the Adobe certificate is also not the only possible attack vector, as Android has at least two other hard-coded certificates that grant applications special access.
One is a certificate for mobile device management technology developed by a company called 3LM that was acquired in early 2011 by Motorola Mobility, before Google acquired Motorola Mobility.
The 3LM device management extensions are not part of the Android Open Source Project (AOSP), but are included in various devices that were produced and shipped by Sony, HTC, Motorola, Samsung, LG and a couple of other smaller manufacturers, Forristal said.
Any application with the 3LM certificate in its certificate chain can use the device management extensions to silently install new apps, change system settings and take control of the device, he said.
Finally, a third hard-coded certificate is used by Google Wallet and provides access to the hardware-based NFC (near-field communication) secure element that's used to store sensitive information like credit card numbers during payment processing.
The Bluebox security researchers didn't have time to analyze the impact of this attack vector in detail, but its mere existence likely violates the Android security model for the NFC secure element, Forristal said.
The certificate chain validation vulnerability, which Bluebox has dubbed Fake ID, was reported to Google in April and a patch was made available to device manufacturers, according to Forristal.
"After receiving word of this vulnerability, we quickly issued a patch that was distributed to Android partners, as well as to AOSP," a Google representative said Tuesday via email. "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."
Motorola has released updates with the patch for some devices and more vendors will probably do the same over the coming weeks, Forristal said.
However, due to the fragmentation of the Android ecosystem, update availability and delivery vary widely between different manufacturers and carriers. Some affected devices are most likely not even supported anymore and will never receive a patch for this issue.
Bluebox has released a free application that can check whether a device is vulnerable to the fake ID attacks.
Forristal plans to discuss the vulnerability in more detail during a presentation at the Black Hat security conference in Las Vegas next week.
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