CVE-2023-20951: A Deep Dive into the Android Out-of-Bounds Write Vulnerability in gatt_process_prep_write_rsp of gatt_cl.cc

In the world of cybersecurity, a Common Vulnerabilities and Exposures (CVE) ID is essential for tracking and mitigating potential vulnerabilities that can affect software systems. CVE-2023-20951 is one such vulnerability that has been identified in Android's Generic Attribute Profile (GATT). This post aims to provide a comprehensive overview of the vulnerability, including its nature, the associated risks, and feasible exploitation methods.

Vulnerability Overview

The vulnerability in question exists in the gatt_process_prep_write_rsp function of the gatt_cl.cc source file in Android's GATT implementation. It is an out-of-bounds write vulnerability due to a missing bounds check which, if exploited, could permit an attacker to remotely execute code without any additional privileges. Moreover, no user interaction is required to carry out this exploitation. The flaw affects Android versions 11, 12, 12L, and 13, making it a critical issue to address.

Here's a snippet of the vulnerable function in gatt_cl.cc

static void gatt_process_prep_write_rsp(tGATT_TCB* p_tcb, uint8_t op_code,
                                        BT_HDR* p_msg) {
  ...
  auto& buf = *p_rcb->p_clcb->p_src_data;

  if (p_rcb->offset < buf.size()) {
    p_value = p_rsp->value.get() + buf.size() - len;
    p_value_src = buf.data();

    // Out-of-bounds write occurs here:
    memcpy(p_value, p_value_src, len);
  }
  ...
}

Notice the lack of bounds checking while performing memcpy, which results in an out-of-bounds write.

Bugreport can be found here

- AOSP Bug Tracker

For more information related to the Android Bluetooth stack and its security implications, refer to these resources:

- Android Security Bulletin
- Android Bluetooth Low Energy Overview

Exploit Scenario

Imagine a scenario in which an attacker is within Bluetooth range of a vulnerable Android device. By manipulating (spoofing) a Bluetooth Low Energy (BLE) peripheral device, the attacker could initiate a GATT communication exchange with the target Android device. The attacker can then send a crafted response packet which triggers the out-of-bounds write vulnerability in the gatt_process_prep_write_rsp function. As a result, an attacker may remotely execute arbitrary code with the same privileges as the Android Bluetooth subsystem, leading to potential device compromise.

Mitigations & Recommendations

To mitigate this vulnerability, it is critical to promptly apply the latest Android security patches, which address this and other security issues. Stay informed of the latest Android vulnerabilities and patches by regularly visiting the official Android Security Bulletin. Furthermore, disabling unnecessary Bluetooth features and ensuring that Bluetooth is only activated when required can minimize the risk of exploitation.

Conclusion

CVE-2023-20951 is a critical out-of-bounds write vulnerability in Android's GATT implementation. If left unpatched, it can leave an Android device exposed to remote code execution attacks, with no user interaction necessary for exploitation. To protect your device, it is essential to install the latest security updates and adopt secure Bluetooth usage practices. Always remember that cybersecurity is a continuous and evolving process that requires ongoing vigilance.

Timeline

Published on: 03/24/2023 20:15:00 UTC
Last modified on: 03/29/2023 07:31:00 UTC