CVE-2026-31574: Linux Kernel DOS Vulnerability

CVE-2026-31574 Overview

CVE-2026-31574 is a kernel vulnerability affecting the Linux kernel's clockevents subsystem. The vulnerability stems from missing resets of the next_event_forced flag in the timer interrupt starvation prevention mechanism. This flaw can lead to system stalls and denial of service conditions when the flag becomes stale during clock event state transitions or when non-forced events are armed.

Critical Impact
This vulnerability can cause system stalls and missed timer interrupts, potentially leading to denial of service conditions on affected Linux systems.

Affected Products

Linux Kernel (all affected versions prior to patch)

Discovery Timeline

2026-04-24 - CVE CVE-2026-31574 published to NVD
2026-04-27 - Last updated in NVD database

Technical Details for CVE-2026-31574

Vulnerability Analysis

This vulnerability exists within the Linux kernel's clockevents subsystem, specifically in the timer interrupt starvation prevention mechanism. The core issue involves the next_event_forced flag not being properly reset in several critical code paths, which can result in timer-related stalls affecting system stability.

The vulnerability manifests in three distinct scenarios:

Clock Event State Changes: When the clock event device transitions through a shutdown/startup sequence, the next_event_forced flag can become stale, persisting across state changes where it should have been cleared.
Non-Forced Event Arming: When a non-forced timer event is armed, the failure to reset the flag prevents rearming before that event fires. If the scheduled event is far in the future, this creates a window where timer interrupts can be missed.
Suspend Wakeup Handler: The suspend/resume path similarly fails to reset the flag, potentially causing timer-related issues after system wake-up events.

Root Cause

The root cause is the absence of proper flag state management in the clockevents subsystem. The next_event_forced flag is designed to prevent timer interrupt starvation, but the implementation failed to reset this flag in multiple code paths where state transitions occur. This oversight allows the flag to retain stale values that no longer reflect the actual intended behavior, causing the timer subsystem to malfunction under specific conditions.

Attack Vector

This vulnerability requires local access to the system to trigger. An attacker with local privileges could potentially exploit this flaw to cause denial of service by manipulating timer-related system calls or triggering specific clock event state transitions that expose the stale flag condition. The attack does not require user interaction and affects system availability by causing stalls and missed timer interrupts.

The vulnerability exploitation would involve triggering clock event state changes in a manner that leaves the next_event_forced flag in an inconsistent state, subsequently leading to timer interrupt starvation and system responsiveness issues.

Detection Methods for CVE-2026-31574

Indicators of Compromise

System log entries indicating timer-related stalls or missed interrupts
Kernel messages showing clockevents subsystem warnings or errors
Unexpected system hangs or unresponsive periods during normal operation
Increased CPU softlockup warnings in kernel logs

Detection Strategies

Monitor kernel logs (dmesg) for clockevents-related error messages and timer stall warnings
Implement system health monitoring to detect unexpected latency spikes or timer anomalies
Use kernel tracing tools (ftrace, perf) to monitor clockevents subsystem behavior
Deploy endpoint detection solutions capable of identifying kernel-level anomalies

Monitoring Recommendations

Enable kernel audit logging to capture timer subsystem events and state transitions
Configure alerting for system stall events and softlockup detection messages
Monitor system uptime and responsiveness metrics for anomalies indicating timer issues
Implement continuous kernel integrity monitoring on production systems

How to Mitigate CVE-2026-31574

Immediate Actions Required

Update the Linux kernel to a patched version that includes the next_event_forced flag reset fixes
Review and apply available kernel patches from the official Linux kernel stable branches
Schedule maintenance windows for kernel updates on production systems
Consider temporarily reducing workloads on affected systems until patches are applied

Patch Information

The Linux kernel development team has released patches to address this vulnerability by adding the missing resets of the next_event_forced flag in all affected code paths. The patches are available through the official kernel stable branches:

These commits add proper flag resets during clock event state changes, non-forced event arming, and in the suspend wakeup handler.

Workarounds

No official workarounds are available; applying the kernel patch is the recommended remediation
Consider implementing system monitoring to detect and respond to timer-related stalls
Enable watchdog timers to automatically recover from system stalls caused by this vulnerability
Reduce the frequency of suspend/resume cycles on critical systems until patched

bash

# Check current kernel version and update to patched version
uname -r
# Update kernel using your distribution's package manager
# For Debian/Ubuntu:
sudo apt update && sudo apt upgrade linux-image-generic
# For RHEL/CentOS:
sudo yum update kernel
# Reboot to apply the new kernel
sudo reboot