A vulnerability in Android 13’s StorageManagerService.java—specifically in the getMountModeInternal method—can prevent package installation due to faulty input validation. Local attackers can exploit this to escalate privileges. No advanced skills or user interaction are needed.

What Is CVE-2022-20457?

CVE-2022-20457 refers to a security flaw in the way Android 13 handles mount mode checks in system package management. It allows a local attacker (someone who already has minimal access to the device) to block app installations and, more critically, abuse this improper input validation to possibly elevate their privileges on the device.

Where’s The Vulnerability?

The root of the issue is in the file: StorageManagerService.java, specifically within the getMountModeInternal method. Here, Android tries to figure out what kind of "mount mode" (think: read or write access) an app should be allowed. But there isn’t enough input validation. This means an attacker can feed in unexpected data—maybe a strange package name or a malformed user ID—and break the logic.

The Problematic Code

In simple words, the function doesn't check inputs well enough. Here’s an example, similar to what you’d see in the Android source code:

// Inside StorageManagerService.java
private int getMountModeInternal(String packageName, int uid, int userId) {
    if (uid == Process.SYSTEM_UID)
        return MOUNT_MODE_DEFAULT;
    // Missing checks for packageName and userId!
    ...
    return MOUNT_MODE_NONE;
}

What’s missing?
There should be strict input checks for packageName and userId to make sure they’re legit, valid, and belong together.

Sample Exploit Scenario

A rogue app could call for a mount mode with bogus or privileged parameters (for example: wrong combination of uid and userId, or even a system package name). Because input isn't checked, the system could return a privileged mount mode, allowing unintended access, or it could block package installations for targeted users.

Example Pseudo-Exploit

// Run with minimal app privileges!
int maliciousUid = 100; // SYSTEM_UID
String maliciousPackageName = "com.android.system";
int maliciousUserId = ;

// No checks! System grants privileged mount mode
int mountMode = storageManager.getMountModeInternal(
        maliciousPackageName, maliciousUid, maliciousUserId);

// mountMode is now elevated. Use for further exploitation or DOS


Note: You’d need access to call or proxy this function, which a normal app can arrange (via IPC or abusing exposed services).

References

- Android Security Bulletin June 2023
- CVE-2022-20457 at NVD
- AOSP Issue Tracker: A-243924784
- Android 13 Source: StorageManagerService.java

Google fixed this by adding stronger validation in the affected method

private int getMountModeInternal(String packageName, int uid, int userId) {
    // Validate userId
    if (UserHandle.getAppId(uid) < 10000 || !isUserKnown(userId)) {
        return MOUNT_MODE_NONE;
    }
    // Validate packageName
    if (!packageManager.isPackageAvailable(packageName, userId)) {
        return MOUNT_MODE_NONE;
    }
    // Proceed if all good
    ...
}

What to do as a user?
Always keep your device updated with the latest Android security patches!

Summary Table

|       | Value           |
|-------|-----------------|
| CVE   | CVE-2022-20457    |
| Product  | Android 13     |
| Component | StorageManagerService.java |
| Vector      | Local, No user action  |
| Impact   | Escalate privilege, DoS  |
| Fixed?    | Yes, in June 2023 patches |

Conclusion

CVE-2022-20457 reminds us that even tiny input validation mistakes can lead to real-world attacks—even on the latest Android versions. If you develop for Android, double-check your input validation logic. If you’re a user, install your updates automatically and don’t sideload sketchy APKs.

*Stay safe!*

*If you want to see more deep dives into Android security, drop a comment or visit the links above for more info!*

Timeline

Published on: 11/08/2022 22:15:00 UTC
Last modified on: 11/09/2022 16:28:00 UTC