CVE-2023-21113 is a security vulnerability discovered in the Android platform. This flaw arises from a common security issue called a confused deputy problem, allowing local attackers to bypass certain permissions and gain elevated privileges on affected devices — all without needing user interaction, and without requiring additional permissions themselves. The vulnerability is especially dangerous since attackers don’t need to trick the user or have any special access ahead of time.

The Confused Deputy Problem

A *confused deputy* happens when a privileged process unwittingly uses its own permissions on behalf of another, less-privileged process. In this context, a malicious app can trick a system service or component into performing actions it shouldn’t, using the system’s higher privileges.

For CVE-2023-21113, this scenario played out across several locations in Android, exposing a surface for attackers to escalate their privileges on the device.

Affected Versions

Google's Android Security Bulletin - May 2023 lists CVE-2023-21113 as affecting a wide range of Android versions, primarily those prior to the listed security patch.

Exploit Details (Step by Step)

Let’s walk through a simplified version of what an attacker might do to exploit CVE-2023-21113. We’ll focus on the pattern, not on targeting any one device or service.

1. Finding the Deputy

Some system service exposes an API – say, via a bound service or a broadcast receiver – that does a privileged operation internally. However, it doesn't really check who’s requesting it. It just does the work for whoever asks.

2. Confusing the Deputy

The attacker (a normal app) communicates with the service in a crafted way, so the service ends up using its own system permissions to perform an operation the attacker couldn't do directly.

3. Attacker Gains Elevated Privileges

The attacker then receives the data or result, now with the higher privileges they didn’t have before.

Suppose there's a system Service with a method like this (Java pseudocode)

public void doPrivilegedStuff(Intent intent, IBinder callback) {
    // Check who is calling? Oops, not really.
    String secret = getSecretData(); // System permission needed here!
    // Returns the result to the caller
    IRemoteCallback cb = IRemoteCallback.Stub.asInterface(callback);
    cb.onResult(secret);
}

Now, as an attacker, I create an app that binds to this service

Intent intent = new Intent();
intent.setComponent(new ComponentName("com.android.system", "SystemService"));

ServiceConnection conn = new ServiceConnection() {
    @Override
    public void onServiceConnected(ComponentName name, IBinder service) {
        // Send a crafted intent
        ISystemService proxy = ISystemService.Stub.asInterface(service);
        proxy.doPrivilegedStuff(new Intent(), myCallback);
    }
};

context.bindService(intent, conn, Context.BIND_AUTO_CREATE);

When the malicious app receives the callback, it gets privileged data it should not have access to!

Impact

- No special permissions needed: Attackers don’t need any clever social engineering or extra app permissions.
- No user interaction: The user does not need to do anything — just installing the malicious app can allow exploitation.
- Local escalation of privilege: Allows the attacker to do things that should be limited to system or privileged components.

Original References

- Google Android Security Bulletin – May 2023
- Official Android CVE Listing
- Exploit Details on Android Security Bug Tracker (restricted)

Mitigation

If you’re a user:

Make sure your device is updated with the latest security patches from your device vendor.

If you’re an Android OEM or system developer:
- Carefully check all service, content provider, or broadcast receiver interfaces for proper caller permission checks.
- Avoid letting privileged system services perform sensitive actions solely based on data or intents provided by untrusted sources.

Conclusion

CVE-2023-21113 is a pocket-sized, high-impact vulnerability that exploits lapses in Android's privilege boundaries. By leveraging the confused deputy problem, attackers could quietly elevate their privileges with zero user interaction. This highlights why it’s important to harden inter-process communication points and always validate the identity and permissions of callers in system-level components.

Stay safe — keep your device patched!

*This post was written for educational purposes, not for exploitation. Always follow local laws and ethical guidelines when researching or reporting vulnerabilities.*

Timeline

Published on: 07/09/2024 21:15:10 UTC
Last modified on: 07/11/2024 15:05:05 UTC