CVE-2022-42895: Linux Kernel Information Disclosure Flaw

CVE-2022-42895 Overview

CVE-2022-42895 is an information disclosure vulnerability in the Linux kernel's Bluetooth L2CAP (Logical Link Control and Adaptation Protocol) implementation. The flaw exists in the l2cap_parse_conf_req function within net/bluetooth/l2cap_core.c, where the code attempts to access uninitialized memory. This vulnerability can be exploited remotely by an attacker within adjacent network range to leak kernel pointers, potentially enabling further exploitation such as bypassing kernel address space layout randomization (KASLR).

Critical Impact

Attackers within Bluetooth range can remotely leak sensitive kernel memory addresses, potentially defeating KASLR and enabling more sophisticated attacks against the Linux kernel.

Affected Products

• Linux Kernel (all versions prior to the security patch)
• Systems with Bluetooth L2CAP functionality enabled
• Devices running unpatched Linux distributions with Bluetooth support

Discovery Timeline

• 2022-11-23 - CVE CVE-2022-42895 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2022-42895

Vulnerability Analysis

This vulnerability is classified as CWE-824 (Access of Uninitialized Pointer), a type of memory information disclosure weakness. The flaw occurs in the Bluetooth L2CAP subsystem of the Linux kernel, specifically within the configuration request parsing logic. The vulnerability allows an attacker on an adjacent network (within Bluetooth range) to trigger the information leak without requiring any privileges or user interaction.

The attack exploits a logic error where the code accesses EFS (Extended Flow Specification) structure fields without first verifying that a remote EFS option was actually received. This leads to the use of uninitialized stack memory, which may contain sensitive kernel pointer values that can be leaked to the attacker.

Root Cause

The root cause lies in the l2cap_parse_conf_req function failing to validate whether a remote EFS structure was actually received before accessing its fields. When the FLAG_EFS_ENABLE flag is set on a channel but no remote EFS option was provided in the configuration request, the code would access the uninitialized efs structure on the stack. This uninitialized memory could contain kernel pointers from previous function calls, which would then be processed and potentially leaked to the remote attacker.

Attack Vector

An attacker within Bluetooth range can send specially crafted L2CAP configuration requests to a vulnerable Linux system. By manipulating the configuration options, the attacker can trigger the vulnerable code path where the kernel accesses uninitialized EFS structure data. The leaked kernel pointers can then be used to defeat KASLR protections, making subsequent memory corruption exploits more reliable.

 			l2cap_add_conf_opt(&ptr, L2CAP_CONF_RFC,
 					   sizeof(rfc), (unsigned long) &rfc, endptr - ptr);
 
-			if (test_bit(FLAG_EFS_ENABLE, &chan->flags)) {
+			if (remote_efs &&
+			    test_bit(FLAG_EFS_ENABLE, &chan->flags)) {
 				chan->remote_id = efs.id;
 				chan->remote_stype = efs.stype;
 				chan->remote_msdu = le16_to_cpu(efs.msdu);

Source: GitHub Linux Commit

The patch adds a check for the remote_efs variable to ensure that the remote EFS option was actually received before accessing the efs structure fields, preventing the use of uninitialized memory.

Detection Methods for CVE-2022-42895

Indicators of Compromise

• Unusual Bluetooth L2CAP configuration request traffic from unknown devices
• Suspicious pairing attempts or connection requests from devices within Bluetooth range
• Unexpected L2CAP channel establishment activity in system logs
• Evidence of Bluetooth scanning activity targeting the system

Detection Strategies

• Monitor kernel logs for L2CAP-related errors or warnings using dmesg or journalctl
• Deploy network monitoring solutions capable of inspecting Bluetooth traffic for anomalous L2CAP configuration requests
• Use intrusion detection systems with rules to detect Bluetooth-based exploitation attempts
• Implement endpoint detection solutions like SentinelOne that can identify kernel-level exploitation attempts

Monitoring Recommendations

• Enable verbose Bluetooth logging on critical systems using btmon or similar tools
• Configure centralized logging to aggregate Bluetooth subsystem events across the environment
• Establish baselines for normal Bluetooth activity to identify anomalous connection patterns
• Deploy SentinelOne agents to monitor for suspicious kernel memory access patterns

How to Mitigate CVE-2022-42895

Immediate Actions Required

• Update the Linux kernel to a version containing commit b1a2cd50c0357f243b7435a732b4e62ba3157a2e or later
• Apply vendor-specific kernel patches from your Linux distribution
• Disable Bluetooth functionality on systems where it is not required
• Restrict physical access to systems to limit Bluetooth attack surface

Patch Information

The vulnerability has been addressed in the upstream Linux kernel. The fix is available in commit b1a2cd50c0357f243b7435a732b4e62ba3157a2e which adds proper validation of the remote_efs variable before accessing EFS structure fields. System administrators should apply kernel updates from their Linux distribution that include this patch.

For reference:

• GitHub Linux Commit
• Kernel Dance Reference

Workarounds

• Disable Bluetooth on systems where it is not required to eliminate the attack surface
• Use Bluetooth management tools to restrict discoverable mode and limit pairing capabilities
• Implement physical security controls to prevent adversaries from approaching within Bluetooth range
• Blacklist the bluetooth kernel module on systems that do not require Bluetooth functionality

# Disable Bluetooth kernel module
echo "blacklist bluetooth" >> /etc/modprobe.d/blacklist-bluetooth.conf
echo "blacklist btusb" >> /etc/modprobe.d/blacklist-bluetooth.conf

# Disable Bluetooth service
systemctl disable bluetooth
systemctl stop bluetooth

# Verify Bluetooth is disabled
rfkill block bluetooth