Recently, a new security vulnerability known as CVE-2018-9475 has been discovered, and it could lead to remote escalation of privilege via Bluetooth. As scary as it sounds, this exploit puts any user who has enabled SIP calls on their devices at risk, with no additional execution privileges needed. What's even worse is that user interaction is not required for this exploit to be successful.

In this in-depth analysis, we will closely examine the security weakness in HeadsetInterface::ClccResponse of btif_hf.cc file, which allows an out of bounds stack write due to a missing bounds check. We will also provide you with crucial information on how this vulnerability can be exploited and how to protect your devices from any potential attacks.

The Vulnerability: HeadsetInterface::ClccResponse in btif_hf.cc

The source of this exploit lies in the HeadsetInterface::ClccResponse function within the btif_hf.cc file, which is a part of the Android Bluetooth component. The vulnerability occurs due to a missing bounds check, which gives the attacker an opportunity to perform an out-of-bounds stack write operation.

Here's a code snippet of the vulnerable function (Source: Android Open Source Project):

static bt_status_t clcc_response(bt_bdaddr_t *bd_addr, int index, int dir, int status, int mode, bool mpty, const char *number, int type) {
    CHECK_BTHF_INIT();

    tBTA_AG_RES res = BTA_AG_OK;
 //_BTA_AG_CLCC_RESPONSE Length value is 20(GTA_AG_CLCC_NUM_LEN - 3)._
    char clcc_str[BTA_AG_CLCC_NUM_LEN - 3];

    // snprintf (below) checks number is not null
    if (number == NULL) {
        res = BTA_AG_ERR_INV_CHAR;
    }

    if (is_valid_ring_address(bd_addr)) {
        snprintf(clcc_str, sizeof(clcc_str), "+CLCC: %d,%d,%d,%d,%d", index, dir, status, mode, mpty);
        BTA_AgResult(RingDevice.bd_addr_handle, res,
                    number ? btif_hf_telecom_format_number(clcc_str, sizeof(clcc_str),
                                    number, type) : cl_cc_str);
    } else {
        APPL_TRACE_WARNING("%s: different_address_connected", __PRETTY_FUNCTION__);
        res = BTA_AG_ERR_OP_NOT_SUPPORTED;
    }

    return btif_transfer_context(btif_hf_to_ag_result_code,
                                  (uint16_t)res, NULL, ,
                                  (const bt_bdaddr_t *)bd_addr);
}

The vulnerable part of the code is the following line

snprintf(clcc_str, sizeof(clcc_str), "+CLCC: %d,%d,%d,%d,%d", index, dir, status, mode, mpty);

It is here where the clcc_str buffer's size is improperly checked. If the number variable contains a sufficiently large value, it can easily cause a buffer overflow. This provides the attacker with the capability to overwrite the stack and potentially execute their malicious code remotely.

Exploiting the Vulnerability

For the exploitation to be successful, the attacker needs access to the target victim's device with Bluetooth capabilities and an active SIP call. The attacker then sends a specially crafted SIP message containing a large number value. This can cause the stack buffer overflow and eventually escalate their privileges on the victim's device.

Since no user interaction is needed for this exploit, the victim may not even notice the attack. This makes CVE-2018-9475 a dangerous and potent vulnerability.

Protecting Your Device

To securely defend against this exploit, it's essential to keep your devices updated. Google has released a security patch (Android Security Bulletin October 2018) to fix this vulnerability, and it is recommended to update your device to the latest Android version possible as soon as possible.

Additionally, it is advised to follow best practices when using Bluetooth on your devices, such as not connecting to unknown devices and turning off Bluetooth when not in use.

In conclusion, CVE-2018-9475 is a severe vulnerability found in the HeadsetInterface::ClccResponse function of btif_hf.cc due to a missing bounds check. It can lead to remote escalation of privilege via Bluetooth, especially if the target victim has enabled SIP calls. However, by keeping your devices up-to-date and following the best Bluetooth security practices, you can protect yourself from this exploit.

Timeline

Published on: 11/20/2024 18:15:19 UTC
Last modified on: 12/18/2024 15:13:24 UTC