Summary:
CVE-2025-22438 is a critical use-after-free vulnerability in the Android framework, specifically in the InputDispatcher.cpp file. Attackers exploiting this flaw can potentially escalate their privileges on a vulnerable device—no additional permissions or user interaction required.

This post offers a deep, step-by-step look at how the bug happens, the exploit details, and prevention tips. We’ll also show some code snippets and link you to authoritative sources.

Background: What is InputDispatcher.cpp?

InputDispatcher.cpp is part of the Android source code that handles input events (like touches and key presses) from the system to apps. The function afterKeyEventLockedInterruptable() processes these key events. Unfortunately, a bug in memory management in this function can let a local attacker mess with pointers after the memory they reference is freed—a "use-after-free" scenario.

Use-after-free bugs can be powerful weapons for escalating privileges or compromising a device, since they may allow bad actors to control memory and inject malicious logic.

Vulnerability Details

The heart of the problem is that afterKeyEventLockedInterruptable() accesses objects in memory after they have been freed. This opens the door for attackers to manipulate the state of the program by making a malicious object appear at the location of the freed object.

Below is a simplified illustration of the problematic function in InputDispatcher.cpp

void InputDispatcher::afterKeyEventLockedInterruptable(KeyEntry* keyEntry) {
    // ... previous operations ...

    // Call that may free or invalidate keyEntry
    if (shouldRemoveKeyEntry(keyEntry)) {
        removeKeyEntryLocked(keyEntry);  // Frees keyEntry in certain cases
    }

    // Use-after-free bug: keyEntry may be gone, but we use it anyway!
    if (keyEntry->someFlag) {            // <--- DANGEROUS
        doSomething(keyEntry);
    }

    // ... rest of the logic ...
}

If removeKeyEntryLocked() frees or otherwise invalidates keyEntry, but code after that still uses it, anything can happen—crash, or worse, exploit.

The attacker can get the system to give them control of the memory at keyEntry and then use the dangling pointer to run arbitrary code.

Exploitation Overview

1. Trigger free: The attacker creates input events that trigger the freeing of a key event object inside the dispatcher.
2. Fill with evil: Right after freeing, the attacker allocates their own object at that memory address.
3. Hijack execution: Since the code later tries to use the now-stale pointer, attacker’s code gets executed.

In pseudo-code, exploiting the bug could go as follows

# 1. Send crafted key events so keyEntry is freed
send_input_event(free_key_entry=True)

# 2. Spray memory with controlled data, such as a malicious object
for i in range(100):
    allocate_object_with_payload(payload=my_shell_code)

# 3. Trigger code that uses keyEntry->someFlag (now points to attacker's object)
send_input_event(trigger_use_after_free=True)

Note: Implementing such an exploit for real would require deep Android internals knowledge. But the key idea is: control the timing of free and allocation to ensure your data occupies the slot of the freed key entry.

Impact

- Local privilege escalation: A normal user can gain higher privileges, potentially full control of the device.

Mitigations

- Patch your OS: Google and Android partners have released patches. Always keep your device updated.
- App Sandboxing: Even though regular apps can attempt this attack, strong process isolation makes exploitation harder. But don't rely just on that.

References & Further Reading

- Android Security Advisory - CVE-2025-22438 *(Update once published)*
- Android InputDispatcher.cpp Source (AOSP)
- Google Security Blog: Use-After-Free Vulnerabilities
- Mitre CVE Details: CVE-2025-22438

Conclusion

CVE-2025-22438 is a textbook example of how a simple use-after-free bug can give attackers total control over a system. Always update your devices and practice defense-in-depth to limit the damage from such unforeseen bugs.

If you're a developer: use smart pointers and double-check resource lifecycles. If you're a user: patch early, patch often!


*If you found this breakdown helpful, share with your team and stay secure!*

Timeline

Published on: 09/02/2025 23:15:35 UTC
Last modified on: 09/04/2025 16:37:48 UTC