Android’s massive ecosystem means vulnerabilities can have wide-reaching impact. One such vulnerability is CVE-2022-20447, discovered in Android 13’s Bluetooth Personal Area Networking (PAN) stack. In this post, I’ll break down exactly what the issue is, how it can be exploited, and why it’s dangerous. We’ll include explanations, code snippets, and all the links you need to dig deeper.

What is CVE-2022-20447?

CVE-2022-20447 is a security bug in Android’s Bluetooth PAN subsystem. The trouble is in the PAN_WriteBuf function (defined in pan_api.cc). There, a use-after-free bug can lead to an _out-of-bounds read_ — meaning data from memory, possibly belonging to other parts of the system, could be read unintentionally.

No extra permissions are needed.

- Could result in information disclosure – attackers could steal sensitive information via Bluetooth.

Android 13

- Android ID: A-233604485

Where’s the Problem? A Simple Explanation

The bug is in the way Android’s PAN_WriteBuf deals with its memory.

- When data buffers are being handled, something may be freed (memory released), but PAN_WriteBuf sometimes still uses the pointer to that freed memory.
- When the code tries to access this freed (now invalid) memory, it can accidentally read unrelated or sensitive data.

This happens in the Bluetooth PAN stack, so any process that can trigger this code over Bluetooth (including remote peers) can, in theory, exploit this bug.

Let’s imagine a simplified code flow

// pan_api.cc (simplified pseudocode)
void PAN_WriteBuf(PAN_CONN *conn, BT_HDR *buf) {
    // ... more setup code ...
    if (some_condition) {
        free(conn->some_buffer);
        // ... oops, but later ...
        process(conn->some_buffer);  // -- UAF occurs here!
    }
    // ... rest of code ...
}

process() might read data from that buffer (READ-after-free).

- That means attackers can cause the system to read and send the wrong memory — leaking secrets over Bluetooth.

What is Use-After-Free?

It’s when the program uses memory *after* it has been released (freed). The old memory might have new, unrelated, or secret values from other parts of the app or another process.

Attacker sends malicious data patterns or triggers specific PAN connection events.

3. These operations mess with the connection buffers, freeing data in a way that leaves a pointer dangling.

PAN_WriteBuf is called and reads from buffer that’s already freed.

5. Memory containing secrets (cookies, app data, keystore bits, etc.) may be packaged and sent back to the attacker.

No user action required. No special privileges. Just proximity + the right crafted Bluetooth traffic.

A (Hypothetical) Exploit Example

Since this is a read (not write) exploitation, it’s mostly useful for stealing data, not gaining code execution.

Attacker records valid PAN traffic between two Android devices.

- Attacker crafts a replay packet with slight manipulation, causing a buffer in the victim’s Bluetooth stack to be freed while PAN_WriteBuf is still referencing it.
- Attacker triggers PAN_WriteBuf to ‘echo’ back memory. The victim unknowingly returns contents of freed memory back via Bluetooth.

Update your Android device!

This bug was fixed in the November 2022 security patch. See if your device has it:
Android Security Bulletins – November 2022

Developers:

Audit your Bluetooth stack. If you’re working on or for a vendor-specific system image, make sure you’re using a patched Bluetooth library.

- Official Android Security Bulletin – November 2022
- NVD Entry for CVE-2022-20447
- AOSP Patch for A-233604485
- Basic Explanation of Use-After-Free
- Source: PAN_WriteBuf function in pan_api.cc (AOSP)

Final Take

CVE-2022-20447 is a risky Bluetooth bug affecting Android 13. It allows an attacker, within Bluetooth range, to extract sensitive info from your device — without you doing anything. The fix is out, so keep your device updated.

If you’re an Android security enthusiast, dissecting this code is a good exercise in identifying subtle, but very real, security hazards in complex memory-managed languages like C and C++.

Keep your system up to date and Bluetooth secure!

*Exclusive: This post provides a clear, easy-to-read technical breakdown not found in other online stories. Stay tuned for more CVE deep-dives!*

Timeline

Published on: 11/08/2022 22:15:00 UTC
Last modified on: 11/09/2022 13:40:00 UTC