---

Android is the world’s most popular mobile operating system, and with its popularity comes continuous scrutiny from the security community. One of the newly identified vulnerabilities impacting Android devices is CVE-2024-23713. This security issue was found in the NotificationManagerService.java class, specifically within the migrateNotificationFilter method. The flaw is tied to faulty input validation, which, as we’ll see, can be exploited locally by malicious applications to escalate privileges—all without user interaction.

Let’s dive in to understand what’s behind CVE-2024-23713, how it can be abused, and how you can protect your device.

What is CVE-2024-23713?

CVE-2024-23713 allows an attacker with local access (such as a malicious app) to get elevated privileges by exploiting improper input validation in Android’s system component responsible for handling notification filters. Due to how some inputs are handled—or *not* handled, to be exact—a privileged action can occur when it shouldn’t, impacting user privacy and device security.

The vulnerability is in the following method inside NotificationManagerService.java

private void migrateNotificationFilter(UserHandle user, NotificationFilter filter) {
    // ... other code ...
    if (filter != null && filter.getAllowedPackages() != null) {
        for (String pkg : filter.getAllowedPackages()) {
            if ( /* missing or weak input validation here */ ) {
                // Add package to notification settings
            }
        }
        // Save the settings
    }
    // ... other code ...
}

Due to lack of proper validation on pkg, a maliciously crafted package name or filter can slip through, manipulating notification settings, which persist *across reboots* and users.

What’s Missing?

Proper input validation for pkg. For example, a malicious app might supply input that tricks the system into updating or migrating notification settings not intended for it.

Vulnerable Code Example

for (String pkg : filter.getAllowedPackages()) {
    // No validation: Is 'pkg' a real package for the calling UID? Is it a reserved name?
    mSettings.addAllowedPackage(pkg);
}

Safer Code Example

for (String pkg : filter.getAllowedPackages()) {
    if (PackageManager.isPackageValid(pkg, user) && !isSystemOrProtectedPackage(pkg)) {
        mSettings.addAllowedPackage(pkg);
    }
}

How Can This Flaw Be Exploited?

A malicious local app could create a fake NotificationFilter object or send a carefully modified intent to the system, making it believe it should migrate or persist certain notification settings for packages it doesn’t own. This could:

Because the migration code runs without verifying the package’s legitimacy, an attacker can tamper with notification system data used by other apps or even the system itself.

Exploit Example (Simplified)

// Pseudocode: running in malicious app context
NotificationFilter filter = new NotificationFilter();
filter.setAllowedPackages(Arrays.asList("com.android.systemui", "com.victim.app"));

// Send the filter to the system (actual exploit details require further reverse engineering):
Intent exploitIntent = new Intent();
exploitIntent.setAction("android.service.notification.MIGRATE_FILTER");
exploitIntent.putExtra("filter", filter);
context.sendBroadcast(exploitIntent);

If the system service receives and acts upon this, notification settings for privileged apps might be changed. On next boot or notification event, the system behaves as if the malicious package was allowed control.

Proof of Concept (POC)

While actual exploitation requires careful crafting and may depend on Android version, here’s the general local attack flow:

Due to lack of checks, system persists notification settings as if the malicious app is trusted.

4. Malicious app either silences system notifications, or sets itself as a handler for notification events.

References & Original Sources

- Android Security Bulletin – June 2024
- AOSP Source: NotificationManagerService.java

Conclusion

CVE-2024-23713 is a classic example of how the smallest gap in input validation—even in tightly controlled system code—can have outsized consequences. This vulnerability could allow a malicious app to escalate privileges and disrupt the user’s notification experience at a deep level. While Google and the Android Open Source Project are expected to patch the issue quickly, awareness and understanding are your best defenses.

If you’re a developer, always validate inputs—especially those that come near system boundaries!

Stay safe, and keep your Android updated.

*This analysis is original work based on publicly available information, intended for educational purposes only. For full technical details, see the links above.*

Timeline

Published on: 05/07/2024 21:15:09 UTC
Last modified on: 07/03/2024 01:48:05 UTC