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Security is supposed to be tight in Android, but sometimes a simple oversight leads to severe consequences. In this deep-dive, we’ll break down CVE-2022-20489—a quiet but dangerous bug that affected multiple versions of Android, letting attackers gain more privilege through a failure to store permissions reliably. We’ll look at how it happened, show you where the code went wrong, and walk through a hypothetical exploitation path, all in plain English.

What is CVE-2022-20489?

CVE-2022-20489 is a vulnerability in the Android operating system—specifically, in the way zen rules (Do Not Disturb rules) are handled in the AutomaticZenRule.java file. This bug affects multiple versions:

File: AutomaticZenRule.java

- Module: Android System UI (Do Not Disturb / Zen Mode)

The bug happens when the code tries but fails to save user- or app-provided permissions, usually because the system runs out of resources (RAM, storage, database connections, etc.). When this save fails, Android may not properly update permissions or configurations, which attackers can exploit to elevate their privileges.

Google’s Issue Tracker for this vulnerability:  
Android Issue A-242703460

Why Is This Bad?

Normally, when an app requests sensitive changes to “Zen” rules (like who can silence the phone or override Do Not Disturb), Android is supposed to check permissions, process the request, and store the change. But if the system is running low on resources, something unexpected happens: the system may silently fail to persist new settings—without warning the user, or fixing things.

This creates a so-called “race condition”: the attacker can “race” the system, force resource exhaustion and apply privileged changes right as the system gives up trying to save security checks. No extra permission or user interaction needed!

Here’s a highly simplified snippet, inspired by the logic around AutomaticZenRule.java

public boolean setZenRule(String ruleId, AutomaticZenRule rule, int userId) {
    if (!hasPermissionToChangeRule(userId)) {
        return false;
    }
    try {
        persistZenRule(ruleId, rule);
    } catch (OutOfResourcesException e) {
        // Oops, saving failed! But we never notify user...
        // BAD: Permission/state might change in memory, but NOT persist on disk
        logError(e);
        // Code fails silently, user isn’t told, attacker profits
        return false;
    }
    return true;
}

If persistZenRule() fails (maybe due to *sqlite database lock*, filesystem full, or memory spike), the change is not committed, but in some cases, the in-memory state may have changed enough for a skilled attacker to exploit until the system restarts.

Here’s how an attacker *could* use this bug to escalate privileges locally

1. Flood or exhaust resources: Fill up disk, drain memory, or otherwise ensure that persistence fails in the AutomaticZenRule.java code.
2. Apply malicious zen rule: Use an app (or code) to add a custom Zen Rule that lets them silence Do Not Disturb (or bypass it) at will.
3. Leverage inconsistent state: If the system is tricked into *thinking* the rule was added (e.g., in memory), but it’s not persisted, the attacker may get temporary privileged access (silence notifications, mask alarms, etc.) or even bypass security checks relying on Zen rules.
4. Repeat as needed: The attack can be repeated, exploiting the window every time the system exhausts its resources.

Bonus: No root, no extra permissions, no user interaction needed (other than installing a local app).

- Android Security Bulletin 2023-01-01 (Google)
- AOSP Diff / Fix (Android 13)
- Permissive Zen Rule reference
- Android Issue A-242703460

How It Was Patched

The fix is now in all supported Android releases. In simple terms, Google patched the vulnerability by:
- On every failure to persist a Zen Rule, forcefully rolling back or cleaning any in-memory or permission state

Making sure apps can’t request privileged rule changes unless persistence succeeds

- Logging and notifying users/admins when something goes wrong (no more silent/fatal fails)

Should I Worry?

You’re safe if you keep your device up-to-date. If you’re on Android 10 through 13 and haven’t updated in a while, you could still be vulnerable to tricky local attacks, especially from untrusted apps.

Final Words

CVE-2022-20489 is a classic example of how modern operating systems can still have “old fashioned” issues—resource exhaustion leading to privilege escalation, all hidden within complicated permission logic no user sees. Always keep your device patched!

Have questions? Drop a note, or check out the AOSP code fix here for more details.

References

1. Android Security Bulletin: CVE-2022-20489
2. Google Issue Tracker: A-242703460
3. AOSP commit diff
4. Zen Mode official docs

Timeline

Published on: 01/26/2023 21:15:00 UTC
Last modified on: 02/01/2023 15:38:00 UTC