CVE-2022-40503 - Bluetooth Host Buffer Over-Read in A2DP Streaming

Bluetooth technology is woven into daily life, powering everything from wireless headphones to smart devices. But sometimes, even widely adopted tech can hide dangerous cracks. In 2022, a critical flaw named CVE-2022-40503 was patched in Android: a buffer over-read vulnerability in the Bluetooth host stack that allowed information disclosure during A2DP streaming.

If you want to truly understand this bug, its risks, and even see how an attacker could exploit it, read on.

What is CVE-2022-40503?

CVE-2022-40503 is a vulnerability found in the way Android’s Bluetooth Host processes A2DP (Advanced Audio Distribution Profile) streams. The problem occurs due to insufficient boundaries checking when handling Bluetooth packets, resulting in an over-read of memory buffers.

Impact:
A remote attacker within Bluetooth range could use a specially crafted packet to read privileged memory. This could leak sensitive info—potentially key chunks of memory or user data.

Where Did the Vulnerability Occur?

The affected code lives in the Bluetooth Host stack, particularly the routines handling A2DP streaming. When a device receives a Bluetooth audio stream, it splits it into packets and processes them. However, because of a missing bounds check, a crafted packet could trick the code to read beyond the intended buffer.

To make it clear, here’s a simplified illustration (not the actual code, but closely modeled)

// Vulnerable routine inside the Bluetooth Host stack
void process_stream_packet(uint8_t *data, size_t len) {
    uint8_t header = data[];
    size_t payload_size = header; // Header says how big the payload is

    // BAD: There's no check if payload_size > len
    uint8_t payload[256];
    memcpy(payload, &data[1], payload_size);

    // ...process payload...
}

The problem:
If the attacker sets a large value in header (say, 255), but sends a short packet (say, 10 bytes), memcpy will read data beyond the end of the data array. This can leak memory content from the host stack, like uninitialized data, previous packets, or even security credentials.

Locate a Target:

The attacker needs to be in Bluetooth range, and the victim device must have Bluetooth turned on and be streaming A2DP audio (like music over headphones).

Send Crafted Packets:

The attacker crafts a special Bluetooth packet for A2DP, with a header value that misleads the code about the actual length of the payload.

Leak Info:

When the host processes the packet, it reads beyond the buffer, pulling in whatever memory bytes are just after. The attacker then listens for any echoes, errors, or protocol states that can reflect back this leaked data, or uses local response timing to infer data.

In practice, getting useful data out isn’t always trivial—sometimes leaked data is random or non-sensitive. But any info disclosure can potentially help attackers escalate privileges or chain with other bugs.

Example Proof of Concept (PoC)

Here’s a toy Python snippet using bluetooth libraries (like pybluez) to send a malformed packet to a Bluetooth device. Note: This is for educational purposes only!

import bluetooth

target_addr = "XX:XX:XX:XX:XX:XX"  # Replace with victim device MAC

# Craft a "fake" A2DP packet
# Normally, 2 bytes header + 20 bytes payload.
# We'll set header to 100, but send only 5 bytes!
packet = bytes([100]) + b'AUDIO'

sock = bluetooth.BluetoothSocket(bluetooth.L2CAP)
sock.connect((target_addr, 25))  # A2DP is usually on PSM 25
sock.send(packet)
sock.close()

You won’t get the full info leak on most patched devices, but on vulnerable stacks, you may cause unpredictable data leakage or even a crash.

Fixes and Mitigations

Android Patch:
The fix is straightforward: always check that the expected payload fits in the actual received data.

// Fixed code
if (payload_size < len) {
    memcpy(payload, &data[1], payload_size);
}

User Steps:
- Update your device: Google patched CVE-2022-40503 in the November 2022 Android security bulletin ([reference below](#references)).

References

- Android Security Bulletin — November 2022
- NVD Entry for CVE-2022-40503
- Bluetooth SIG A2DP Profile
- Generic Bluetooth Security

Takeaway

CVE-2022-40503 reminds us that even low-level protocols like Bluetooth can harbor serious data-leaking bugs. When boundaries are not checked, attackers may slip in and fish for secrets—so always keep your devices up-to-date, and don’t ignore those monthly security patches.

If you’re a developer working with communication stacks, always validate every input, especially headers and lengths. A safe buffer today can prevent a breach tomorrow.

Timeline

Published on: 04/13/2023 07:15:00 UTC
Last modified on: 04/24/2023 15:50:00 UTC