CVE-2026-31459: Linux Kernel Privilege Escalation Flaw

CVE-2026-31459 Overview

CVE-2026-31459 is a memory leak vulnerability in the Linux kernel's DAMON (Data Access MONitor) sysfs interface. The vulnerability occurs in the damon_sysfs_commit_input() function where param_ctx is leaked when damon_sysfs_new_test_ctx() fails. This happens because the early return path skips the cleanup code at the out label, resulting in memory not being properly freed.

Additionally, the DAMON_SYSFS subsystem can perform NULL pointer dereferences when a privileged user executes improper sequences of control operations. This patch series addresses both the memory leak and NULL dereference issues present in the sysfs interface.

Critical Impact

A privileged local attacker could potentially cause memory exhaustion through repeated exploitation of the memory leak, or trigger a kernel crash via NULL pointer dereference through improper control sequences.

Affected Products

• Linux kernel (DAMON sysfs subsystem)

Discovery Timeline

• April 22, 2026 - CVE-2026-31459 published to NVD
• April 23, 2026 - Last updated in NVD database

Technical Details for CVE-2026-31459

Vulnerability Analysis

The vulnerability resides within the DAMON sysfs interface, specifically in the memory management code path of damon_sysfs_commit_input(). When allocation fails during the creation of a new test context via damon_sysfs_new_test_ctx(), the function returns early without properly destroying the previously allocated param_ctx structure.

Under normal operation, the cleanup of param_ctx occurs at the out label at the end of the function. However, the early return on allocation failure bypasses this cleanup path entirely, leaving the allocated memory orphaned. This constitutes a classic memory leak pattern in kernel code.

The associated NULL pointer dereference vulnerability occurs when privileged users issue control operations in an incorrect sequence, causing the kernel to attempt operations on uninitialized or already-freed memory structures.

Root Cause

The root cause is improper error handling in the damon_sysfs_commit_input() function. When damon_sysfs_new_test_ctx() returns failure, the code performs an early return that bypasses the out label where param_ctx destruction occurs. The fix ensures that param_ctx is properly destroyed before the early return.

Attack Vector

The attack requires local access with elevated privileges to interact with the DAMON sysfs interface. An attacker would need to:

1. Trigger repeated allocation failures in damon_sysfs_new_test_ctx() to cause memory leaks
2. Or issue improper control sequences through the sysfs interface to trigger NULL pointer dereferences

While this requires privileged access, the vulnerability could be exploited as part of a privilege escalation chain or to cause denial of service conditions on systems where DAMON is enabled.

Detection Methods for CVE-2026-31459

Indicators of Compromise

• Unusual memory consumption growth in kernel space over time
• Kernel oops or panic messages referencing DAMON sysfs functions
• Unexplained system instability when DAMON features are in use
• Kernel log entries showing NULL pointer dereferences in mm/damon/sysfs.c

Detection Strategies

• Monitor kernel logs for DAMON-related error messages and NULL pointer dereference warnings
• Track kernel memory usage for unexpected growth patterns
• Implement auditd rules to monitor access to DAMON sysfs interface paths
• Use SentinelOne Singularity to detect anomalous kernel behavior patterns

Monitoring Recommendations

• Enable kernel memory leak detection tools such as kmemleak during testing
• Monitor /sys/kernel/mm/damon/ directory for suspicious access patterns
• Implement alerting on kernel oops events related to memory management subsystems

How to Mitigate CVE-2026-31459

Immediate Actions Required

• Update to patched Linux kernel versions that include the fix commits
• Restrict access to DAMON sysfs interfaces to only necessary privileged users
• Monitor systems for signs of exploitation while awaiting patches
• Consider disabling DAMON if not required in production environments

Patch Information

The Linux kernel maintainers have released patches to address this vulnerability. The fix ensures that param_ctx is properly destroyed before the early return when damon_sysfs_new_test_ctx() fails. The following kernel commits contain the fix:

• Kernel Git Commit 7fe000eb
• Kernel Git Commit e9de9f3c
• Kernel Git Commit f76f0a96

Administrators should apply kernel updates from their distribution vendor as they become available.

Workarounds

• Restrict access to the DAMON sysfs interface using file system permissions
• Disable the DAMON sysfs interface if not required by setting appropriate kernel configuration options
• Use SELinux or AppArmor policies to limit access to /sys/kernel/mm/damon/ paths

# Restrict access to DAMON sysfs interface
chmod 700 /sys/kernel/mm/damon/
chown root:root /sys/kernel/mm/damon/