In February 2023, Google patched a critical vulnerability in the Android Bluetooth stack, tracked as CVE-2023-20954. This flaw, located in the SDP_AddAttribute function of sdp_db.cc, potentially allows an attacker to achieve remote code execution by sending specially crafted Bluetooth packets.

Let’s break down this vulnerability in simple terms, see the relevant code, walk through how it can be exploited, and discuss mitigation steps.

Component: Bluetooth SDP (Service Discovery Protocol)

- CVE: CVE-2023-20954
- Bug ID: A-261867748

What is the SDP_AddAttribute Vulnerability?

SDP (Service Discovery Protocol) lets Bluetooth devices discover each other’s services. When a device receives a new service attribute, the SDP_AddAttribute function in sdp_db.cc adds it to a database.

The flaw? The function fails to properly check the size of the input. That lets an attacker craft a packet which "tricks" the function into writing data outside allotted memory (buffer overflow). This overflow can change program behavior, crash the Bluetooth process, or allow for remote code execution on the device.

Here’s a simplified version of the vulnerable code before the fix

// sdp_db.cc

BOOL SDP_AddAttribute( tSDP_RECORD *p_rec, UINT16 id, UINT8 type, UINT32 len, UINT8 *p_val ) {
    tSDP_ATTRIBUTE *p_attr;
    
    // ... (Some checks and setup)

    p_attr->id = id;
    p_attr->type = type;
    p_attr->len = len;

    if (len >  && p_val) {
        // 🚨 VULNERABLE: No proper bound check on len vs buffer size
        memcpy(p_attr->value, p_val, len);
    }

    // ... (Rest of function)
    return TRUE;
}

The code assumes that p_attr->value is always big enough for len bytes, but doesn’t check.

- A malicious packet could specify a huge len, letting the attacker write outside the expected memory region.

Exploit Scenario

An attacker within Bluetooth range (up to 10 meters) crafts a malicious SDP packet designed to trigger the bug. Here’s a high-level attack scenario:

Device Discovery: Attacker’s device discovers the vulnerable Android phone over Bluetooth.

2. SDP Packet: Attacker sends a malformed SDP service attribute addition, with an oversized len value and controlled payload.
3. Out-of-bounds Write: The target device receives and processes the packet. The function writes len bytes, overflowing the buffer in memory.
4. Arbitrary Code Execution: With careful construction, the attacker’s payload can overwrite memory in a way that allows them to execute code with the Bluetooth process’s privileges.

The Patch

Google’s fix for this bug adds length checks before copying the attribute data. Here’s the gist of the fixed code:

if (len >  && p_val) {
    if (len <= sizeof(p_attr->value)) {  // ✅ Now checks the len
        memcpy(p_attr->value, p_val, len);
    } else {
        // Handle error: attribute too large
        return FALSE;
    }
}


This ensures attribute data can never overflow the buffer.

See the official patch:

> Reference:  
> Android Open Source Project Commit
>
> > "Check attribute size before memcpy in SDP_AddAttribute()"

Exploit Details

While full public exploits are not (yet) available, the nature of the bug means attackers can craft packets like this (Python pseudocode):

import bluetooth

# Replace with target's address
target_address = "XX:XX:XX:XX:XX:XX"

# Build malformed SDP request (pseudo-protocol)
malicious_len = x100  # very large len
payload = b"A" * malicious_len

# Packet would target the SDP channel, sending over a crafted Attribute Add request
# Actual exploit development would require knowledge of the packet structure

sock = bluetooth.BluetoothSocket(bluetooth.RFCOMM)
sock.connect((target_address, 1))
sock.send(build_sdp_attribute_payload(malicious_len, payload))
sock.close()


With the right payload, this can lead to memory corruption and code execution. In the wild, we have seen similar vulnerabilities chained for both device takeover and lateral movement inside networks.

If you use Android 11, 12, 12L, or 13

- Update immediately. The bug is patched in security updates from February 2023 onwards (Android Security Bulletin).
- If you can’t update, turn off Bluetooth if you’re in a high-risk location or think you might be targeted.

References

- CVE-2023-20954 - NIST
- Android Security Bulletin, Feb 2023
- Patch Commit on Android Open Source Project

Conclusion

CVE-2023-20954 is a textbook example of why strict bounds checking is critical for device security. This Bluetooth flaw lets attackers compromise unpatched Android devices without any interaction, just by being nearby. If you haven’t updated your phone to the latest Android version, now’s the time!

Stay safe, and always keep your device up to date!

Timeline

Published on: 03/24/2023 20:15:00 UTC
Last modified on: 03/29/2023 15:00:00 UTC