CVE-2022-1516: Linux Kernel X.25 Protocol DoS Vulnerability

CVE-2022-1516 Overview

A NULL pointer dereference vulnerability was discovered in the Linux kernel's X.25 set of standardized network protocols functionality. The flaw occurs when a user terminates their session using a simulated Ethernet card and continues usage of this connection. This vulnerability allows a local user to crash the system, resulting in a denial of service condition.

Critical Impact

Local users can exploit this NULL pointer dereference to crash the Linux kernel, causing system-wide denial of service affecting all running processes and services.

Affected Products

• Linux Kernel version 5.18-rc1
• Debian Linux 9.0
• Debian Linux 10.0

Discovery Timeline

• May 5, 2022 - CVE-2022-1516 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2022-1516

Vulnerability Analysis

This vulnerability is classified as both a NULL pointer dereference (CWE-476) and a use-after-free condition (CWE-416) within the Linux kernel's X.25 networking protocol implementation. The X.25 protocol is a legacy packet-switched data network protocol that was commonly used in WAN communications.

The flaw manifests when a local user establishes a connection using a simulated Ethernet card over the X.25 protocol stack. When the user terminates their session but continues to interact with the connection, the kernel fails to properly validate pointer references, resulting in a NULL pointer dereference that triggers a kernel panic.

The vulnerability requires local access to the system and low privileges to exploit, making it primarily a denial of service vector rather than a code execution risk. The attack does not require user interaction and impacts system availability without affecting confidentiality or integrity.

Root Cause

The root cause lies in improper pointer handling within the X.25 protocol implementation. When a session using a simulated Ethernet card is terminated, the kernel fails to properly clean up or validate connection state references. Subsequent operations on the terminated connection attempt to dereference a pointer that has either been freed (use-after-free) or set to NULL, causing the kernel to crash.

The combination of CWE-416 (Use After Free) and CWE-476 (NULL Pointer Dereference) indicates that memory management issues in the session cleanup code path create conditions where stale or invalid pointers are accessed.

Attack Vector

The attack requires local access to the target system with low-level user privileges. An attacker would need to:

1. Establish an X.25 network connection using a simulated Ethernet card interface
2. Terminate the session while maintaining references to the connection
3. Attempt further operations on the terminated connection
4. The kernel dereferences an invalid pointer, causing a system crash

Since the vulnerability is exploited locally and the attack complexity is low, any authenticated user on a vulnerable system can potentially trigger this denial of service condition. The vulnerability does not require any user interaction to exploit.

Detection Methods for CVE-2022-1516

Indicators of Compromise

• Unexpected kernel panics or system crashes associated with X.25 network subsystem
• Kernel crash dumps showing NULL pointer dereference in X.25 related functions
• Unusual activity involving simulated Ethernet card configurations
• Log entries indicating X.25 protocol session termination anomalies

Detection Strategies

• Monitor kernel logs (dmesg, /var/log/kern.log) for NULL pointer dereference errors in X.25 subsystem
• Implement kernel crash analysis to identify patterns matching this vulnerability
• Deploy endpoint detection solutions to monitor for suspicious X.25 protocol activity
• Review system configuration for unnecessary X.25 protocol enablement

Monitoring Recommendations

• Enable kernel auditing for network protocol operations involving X.25
• Configure crash dump collection to capture kernel panics for forensic analysis
• Monitor system uptime and unexpected reboots as potential indicators of exploitation
• Implement SentinelOne Singularity platform for real-time kernel-level threat detection and automated response

How to Mitigate CVE-2022-1516

Immediate Actions Required

• Update the Linux kernel to a patched version containing commit 7781607938c8
• Apply vendor-provided security patches from your Linux distribution
• If X.25 protocol is not required, consider disabling the X.25 kernel module
• Restrict local user access to systems where X.25 functionality is required

Patch Information

The vulnerability has been addressed in the Linux kernel through commit 7781607938c8. The fix is available in the Linux Kernel Commit Update. Debian users should refer to Debian Security Advisory DSA-5173 and the Debian LTS Announcement for distribution-specific patch information.

Additional technical discussion can be found in the Openwall OSS Security Discussion.

Workarounds

• Disable the X.25 kernel module if not required: modprobe -r x25
• Blacklist the X.25 module to prevent automatic loading
• Restrict access to simulated Ethernet card functionality through user permissions
• Implement network segmentation to limit access to systems requiring X.25 protocol

# Configuration example
# Disable X.25 kernel module
sudo modprobe -r x25

# Blacklist X.25 module to prevent automatic loading
echo "blacklist x25" | sudo tee /etc/modprobe.d/blacklist-x25.conf

# Verify module is not loaded
lsmod | grep x25