CVE-2022-4269 Overview
A flaw was found in the Linux kernel Traffic Control (TC) subsystem that allows a local unprivileged user to trigger a CPU soft lockup condition. The vulnerability occurs when using a specific networking configuration that redirects egress packets to ingress using the TC action "mirred." When the transport protocol in use (TCP or SCTP) performs a retransmission under these conditions, an ABBA deadlock can occur, resulting in a denial of service condition.
Critical Impact
Local unprivileged users can cause complete system unresponsiveness through CPU soft lockup, impacting system availability and potentially requiring a hard reboot to recover.
Affected Products
- Linux Kernel (versions from 4.1-rc1 and later)
- linux linux_kernel
- Debian-based distributions using affected kernel versions
Discovery Timeline
- December 5, 2022 - CVE CVE-2022-4269 published to NVD
- April 14, 2025 - Last updated in NVD database
Technical Details for CVE-2022-4269
Vulnerability Analysis
This vulnerability stems from an ABBA deadlock condition (CWE-833: Deadlock) in the Linux kernel's Traffic Control subsystem. The issue manifests when network traffic is configured to use the "mirred" TC action, which redirects egress packets back to ingress. This creates a circular packet flow that, under specific circumstances involving TCP or SCTP retransmissions, leads to a deadlock scenario.
The deadlock occurs because two locks are acquired in reverse order by different code paths. When a packet is redirected from egress to ingress while a retransmission is occurring, the system attempts to acquire locks in conflicting orders across different execution contexts, causing a classic ABBA deadlock pattern. This results in a CPU soft lockup that renders the affected system unresponsive.
Root Cause
The root cause is an improper lock ordering in the Traffic Control subsystem when handling packets that are redirected from egress to ingress via the mirred action. The vulnerability is classified as CWE-833 (Deadlock), indicating that the system can enter a state where two or more threads are blocked forever, each waiting for resources held by the other. The specific trigger requires the transport layer (TCP or SCTP) to perform retransmission while packets are being redirected through the mirred action.
Attack Vector
The attack vector is local, requiring the attacker to have local access to the system. An unprivileged user can exploit this vulnerability by:
- Configuring TC rules that redirect egress traffic to ingress using the mirred action
- Generating network traffic that triggers TCP or SCTP retransmissions under this configuration
- The combination of these conditions causes the kernel to enter a deadlock state, resulting in CPU soft lockup
The exploitation does not require elevated privileges, making it accessible to any local user with the ability to configure traffic control rules or generate network traffic on interfaces with such configurations already in place.
Detection Methods for CVE-2022-4269
Indicators of Compromise
- Kernel log messages indicating CPU soft lockup conditions (BUG: soft lockup - CPU#X stuck for Xs!)
- System unresponsiveness or hung processes related to network operations
- Presence of TC rules using the mirred action redirecting egress to ingress (tc filter show and tc action show)
Detection Strategies
- Monitor kernel logs for soft lockup warnings using tools like dmesg or journalctl
- Audit Traffic Control configurations for mirred action rules that redirect egress to ingress
- Deploy kernel-level monitoring to detect prolonged lock contention in networking subsystems
- Use SentinelOne's real-time kernel monitoring capabilities to identify anomalous lock behavior
Monitoring Recommendations
- Implement continuous monitoring of kernel log messages for soft lockup indicators
- Set up alerts for unusual network configuration changes, particularly TC rule modifications
- Monitor system load and CPU utilization for signs of lockup conditions
- Review network traffic patterns for anomalous retransmission behavior on interfaces with mirred configurations
How to Mitigate CVE-2022-4269
Immediate Actions Required
- Update the Linux kernel to a patched version that addresses the deadlock condition
- Review and modify TC configurations to avoid redirecting egress packets to ingress using mirred action
- Restrict access to Traffic Control configuration utilities for unprivileged users
- Monitor affected systems for signs of exploitation while awaiting patch deployment
Patch Information
Patches have been released addressing this vulnerability. Administrators should consult their distribution's security advisories for specific patch information:
The fix involves correcting the lock ordering in the TC subsystem to prevent the ABBA deadlock scenario. Technical details of the patch discussion are available in the Kernel Mailing List Discussion.
Workarounds
- Remove or modify TC rules that use the mirred action to redirect egress traffic to ingress
- Restrict local user access to TC configuration commands using appropriate permission controls
- Consider implementing network namespaces to isolate potentially vulnerable configurations
- Apply kernel live patching solutions if available while planning for a full kernel update
# Check for mirred rules redirecting egress to ingress
tc filter show dev <interface> egress | grep mirred
tc action show action mirred
# Remove problematic mirred rules if found (example)
tc filter del dev <interface> egress
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
