Threat description




Exploit:Android/Masterkey identifies code designed to exploit a known vulnerability in the way the Android operation system verifies the authenticity of an app.


Automatic action

When detected during scanning, F-Secure SAFE will prompt you for a desired action. You may assess the detected file and choose to Uninstall, Quarantine or keep it installed on your device. More information about these options can be found at Help Center: Assess files detected during scanning.


More information on the scanning and removal options available in your F-Secure product can be found in the Help Center.

You may also refer to the Knowledge Base on the F-Secure Community site for further assistance.

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Technical Details

From the F-Secure Mobile Threat Report Q3 2013:

In July [2013], security researchers publicly announced the discovery of a vulnerability in cryptographic signature verification for Android apps that, if exploited, would allow an attacker to modify a legitimate app’s code without affecting its cryptographic signature - essentially keeping the tampering from being detected during verification. Shortly after the announcement, researchers were able to find samples of such modified apps being distributed.

Google was reportedly notified of the "Masterkey" issue earlier in the year, and at the time of the announcement had fixed the issue in the Android open source codebase. Users would however still need to wait for a firmware update from their device manufacturer in order to receive the patched code.

Vulnerability Protection

The vulnerability leveraged by the exploit is application or platform specific; in other words, a specific program (or even a specific version of a particular program) must be installed in order for the exploit to be effective.

To prevent exploitation of such vulnerabilities, please refer to the application or device vendor for the latest updates and additional advice.

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