CVE-2026-53334: Linux Kernel Use-After-Free Vulnerability

CVE-2026-53334 Overview

CVE-2026-53334 is a NULL pointer dereference vulnerability in the Linux kernel's mm/damon/reclaim subsystem. The Data Access MONitor (DAMON) reclaim module fails to handle allocation failures for its damon_ctx object during initialization. When the allocation fails, damon_reclaim_enabled_store() proceeds to call damon_commit_ctx() with a NULL ctx pointer, causing a kernel NULL pointer dereference.

The issue was discovered by Sashiko and reported to the Linux kernel maintainers. The upstream fix returns -ENOMEM when ctx is NULL, preventing the dereference.

Critical Impact
A NULL pointer dereference in kernel memory management code can cause a kernel oops or system crash, resulting in denial of service on affected Linux systems using the DAMON reclaim feature.

Affected Products

Linux kernel versions containing the DAMON_RECLAIM subsystem prior to the fixing commits
Systems with CONFIG_DAMON_RECLAIM enabled
Distributions shipping vulnerable stable kernel branches

Discovery Timeline

2026-07-01 - CVE-2026-53334 published to NVD
2026-07-01 - Last updated in NVD database

Technical Details for CVE-2026-53334

Vulnerability Analysis

DAMON is the Linux kernel's Data Access MONitoring framework used for tracking memory access patterns. DAMON_RECLAIM is a proactive reclamation module built on top of DAMON that identifies cold memory regions and reclaims them.

The module allocates a damon_ctx object during its initialization routine. This object holds the context used by the kdamond kernel thread. The function damon_reclaim_enabled_store(), invoked when userspace writes to the module's sysfs enabled attribute, assumed the allocation always succeeded.

When the allocation failed, execution continued into damon_commit_ctx() while ctx was NULL. Dereferencing this NULL pointer inside kernel context triggers an oops. While the allocation is small and rarely fails on typical systems, memory pressure or fault injection can reliably trigger the condition.

Root Cause

The root cause is a missing NULL check after a kernel memory allocation. The damon_reclaim init path does not propagate the allocation failure state, and the sysfs store handler does not validate ctx before use. This is a classic missing-error-handling bug in kernel initialization code [CWE-476].

Attack Vector

A local user with permission to write to the DAMON reclaim sysfs interface can trigger the code path. Combined with induced memory pressure or allocation failure conditions, this leads to a kernel NULL pointer dereference and system crash. The vulnerability requires local access and does not enable code execution or privilege escalation beyond denial of service.

Exploitation code is not published. The upstream commits 635b45ce61de, 66bc00ea37fa, and 7e2ed8a29427 document the fix by returning -ENOMEM when ctx is NULL.

Detection Methods for CVE-2026-53334

Indicators of Compromise

Kernel oops messages referencing damon_commit_ctx or damon_reclaim_enabled_store in dmesg output
Unexpected system crashes or panics on hosts with CONFIG_DAMON_RECLAIM=y
Repeated writes to /sys/module/damon_reclaim/parameters/enabled from non-administrative processes

Detection Strategies

Inventory Linux kernel versions across the fleet and correlate against the patched stable branches referenced in the upstream commits
Monitor kernel ring buffer logs for NULL pointer dereference traces originating in the mm/damon subsystem
Audit sysfs write activity targeting DAMON reclaim controls to identify anomalous local activity

Monitoring Recommendations

Ship /var/log/kern.log and journald kernel entries to a centralized log platform for anomaly detection
Alert on kernel panic and oops events tied to memory management subsystems
Track unpatched kernel builds using configuration management tooling and vulnerability scanners

How to Mitigate CVE-2026-53334

Immediate Actions Required

Apply the upstream stable kernel patches referenced by commits 635b45ce61de53a9357e28ac97461428cdb650f0, 66bc00ea37fa8ec14be5a3909d067a5967ef234b, and 7e2ed8a29427af534bf2cb9b8bc51762b8b6e654
Update to distribution kernel packages that incorporate the DAMON_RECLAIM allocation-failure fix
Restrict write access to DAMON sysfs interfaces to root only

Patch Information

The fix returns -ENOMEM from damon_reclaim_enabled_store() when the damon_ctx allocation fails, preventing the NULL dereference. A companion patch in the series applies the equivalent fix to DAMON_LRU_SORT. Reference the upstream commits: 635b45ce61de, 66bc00ea37fa, and 7e2ed8a29427.

Workarounds

Disable the DAMON_RECLAIM feature by unloading the module or setting enabled=N where kernel configuration allows
Rebuild custom kernels without CONFIG_DAMON_RECLAIM if the feature is not required
Restrict CAP_SYS_ADMIN and sysfs write permissions to prevent untrusted local users from exercising the vulnerable path

bash

# Verify kernel version and DAMON configuration
uname -r
grep CONFIG_DAMON /boot/config-$(uname -r)

# Disable DAMON reclaim at runtime (if module)
sudo modprobe -r damon_reclaim

# Prevent module autoload
echo 'blacklist damon_reclaim' | sudo tee /etc/modprobe.d/blacklist-damon-reclaim.conf