In 2022, security researchers discovered a startling vulnerability in the Android operating system that could leave your phone or tablet caught in an endless restart loop—effectively bricking it with just a basic local app, no special privileges, and no user interaction. This bug was tracked as CVE-2022-20414 and it affects a wide range of Android versions, from 10 all the way to 13.

In this post, we'll break down how the bug works, why it happens, and how it can be exploited. We'll also look at the vulnerable code and show you where Google patched the issue.

What is the AlarmManagerService and Why Does It Matter?

On Android, AlarmManagerService is a system service that lets apps schedule actions to happen in the future—even if the app isn't running. For example, it’s what lets your calendar send you a reminder at the right time. Because it's a core system service, it's a high-value target for attackers—if they can break it, they can disrupt the whole device.

The Bug: Uncaught Exception Leads to Boot Loop

The vulnerability centers on the setImpl method in AlarmManagerService.java. There, due to improper input handling, it's possible for a local app to trigger an unchecked exception. If this exception happens in a system process, Android design means the process is restarted. But if the process dies while handling critical alarms during startup, this can cause a boot loop—the device restarts continuously, making it unusable.

The critical part? No special permissions required. Any app installed on the device can trigger the bug, and it doesn't need you to do anything—no button tap, no popup.

Here’s a simplified snippet inspired by the vulnerable method (before the patch)

// AlarmManagerService.java
private void setImpl(int type, long triggerAtMillis, long windowMillis, long intervalMillis, 
                     PendingIntent operation, IAlarmListener listener, String listenerTag, 
                     int flags, WorkSource workSource, AlarmClockInfo alarmClock, 
                     int uid, String packageName) 
{
    // ....some code.... 

    // Problem arises when "operation" is null or malformed
    scheduleAlarm(type, triggerAtMillis, operation); 
    // No check if operation is null or valid
}

If an attacker crafts an intent or input that leads operation to be null or malformed, scheduleAlarm throws a NullPointerException. If uncaught, this kills the system server process.

Here’s a hypothetical (simplified) code snippet an attacker could use in an app

Intent intent = new Intent(); // No destination set
PendingIntent pi = null; // Or create one with conflicting parameters

AlarmManager am = (AlarmManager) getSystemService(Context.ALARM_SERVICE);

try {
    am.set(AlarmManager.RTC_WAKEUP, System.currentTimeMillis() + 500, pi);
    // Or pass a malformed pending intent crafted to trigger a bug in AlarmManagerService
} catch (Exception e) {
    // App itself may not crash, but system may be affected
}

This PoC basically asks AlarmManager to set an alarm using a null PendingIntent. Due to the missing input validation, this travels up to the system service, which isn’t expecting a null or broken PendingIntent, causing the crash.

Why the Device Boot Loops

Because AlarmManagerService is a system process and is essential for phone startup, when it fails due to the uncaught exception, the Android runtime restarts the process. But since the condition persists (the malformed alarm is still handled every time), the process dies again, and the cycle repeats—locking the device in a boot loop.

Affected Products: Android 10, 11, 12, 12L, 13

- Patch: The bug was fixed by adding proper null checks and input validation in the setImpl method.

Here’s a representative commit diff (from AOSP code review):

if (operation == null) {
    throw new IllegalArgumentException("operation must not be null");
}
// continue processing only if validation passes

You can check Google's Android Security Bulletin, Nov 2022, where this CVE was addressed.

Additional References

- NVD Entry for CVE-2022-20414
- AOSP Commit Fix for AlarmManagerService
- Original Google Bugtracker Issue A-234441463 *(log in required)*

Mitigation and Advice

If you have a device on Android 10-13, check for security updates from November 2022 or later. Devices with Google Play system updates should already have the fix. If you're a developer, never pass null or malformed PendingIntents to system services. Always validate inputs before calling into Android APIs.

Conclusion

CVE-2022-20414 shows how missing a simple null check in a critical system service can turn into a major device-crippling vulnerability. Luckily, patches are out, and the lesson is clear: always do input validation, especially at system boundaries.

Have thoughts or questions? Let us know in the comments, or check out the linked references for more technical deep dives!

Timeline

Published on: 11/08/2022 22:15:00 UTC
Last modified on: 11/09/2022 15:51:00 UTC