CVE-2026-68283: Linux Kernel Use-After-Free Vulnerability

CVE-2026-68283 Overview

CVE-2026-68283 is a use-after-free vulnerability in the Linux kernel's tracing subsystem. The flaw resides in the event trigger teardown path, where satellite data structures are freed without waiting for concurrent tracepoint handlers to complete. A prior change moved kfree() of event_trigger_data to a kthread that runs tracepoint_synchronize_unregister(), removing the implicit synchronization that trigger .free callbacks previously relied on. As a result, event_hist_trigger_free(), event_hist_trigger_named_free(), and event_enable_trigger_free() release their satellite data (hist_data, cmd_ops, enable_data) while a concurrent tracepoint handler can still reference the trigger through the list_del_rcu()'d entry.

Critical Impact
A local attacker with the ability to configure event triggers can trigger a race that dereferences freed kernel memory, leading to kernel memory corruption, privilege escalation, or denial of service.

Affected Products

Linux kernel versions containing commit 61d445af0a7c ("tracing: Add bulk garbage collection of freeing event_trigger_data")
Distributions shipping affected upstream stable kernels prior to the fix
Systems exposing tracefs event trigger interfaces to privileged users

Discovery Timeline

2026-08-10 - CVE-2026-68283 published to NVD
2026-08-13 - Last updated in NVD database

Technical Details for CVE-2026-68283

Vulnerability Analysis

The vulnerability originates in the Linux kernel's ftrace event trigger infrastructure. Event triggers attach actions to trace events and rely on RCU (Read-Copy-Update) semantics to safely detach entries from live tracepoint handlers. The upstream commit 61d445af0a7c optimized trigger teardown by deferring kfree() calls to a garbage-collection kthread that first calls tracepoint_synchronize_unregister(). This preserved safety for the trigger structure itself but broke an implicit contract with per-trigger .free callbacks.

Three callbacks free satellite data immediately after trigger_data_free() returns: event_hist_trigger_free() releases hist_data, event_hist_trigger_named_free() releases cmd_ops, and event_enable_trigger_free() releases enable_data. Because synchronization now runs asynchronously in the kthread, a tracepoint handler executing on another CPU may still hold a reference to the trigger and reach through it into freed satellite memory. The result is a classic use-after-free [CWE-416].

Root Cause

The root cause is a mismatch between the deferred RCU grace period used to free event_trigger_data and the synchronous free of satellite structures owned by the trigger. Deferring the trigger free without also deferring the dependent frees leaves a window where in-flight tracepoint callbacks dereference dangling pointers.

Attack Vector

An attacker with permission to write to tracefs event trigger files can rapidly register and unregister histogram or enable triggers while generating events that fire those triggers. Racing the teardown against a live tracepoint handler causes the handler to dereference freed hist_data, cmd_ops, or enable_data, corrupting kernel memory.

The upstream fix, applied in commits 79097812153b826fc156a2930ec8a90ed9edf4a2 and b9c8a1400a3bf633f32820d184f3e05fed0f4af7, makes histogram teardown wait on tracepoint_synchronize_unregister() before freeing satellite data. For the enable trigger path, an optional private_data_free() callback runs inside the free kthread after its grace period, freeing enable_data safely without re-serializing the fast path.

Detection Methods for CVE-2026-68283

Indicators of Compromise

Unexpected kernel oops or panic entries in dmesg referencing event_hist_trigger_free, event_enable_trigger_free, or trigger_data_free
KASAN (Kernel Address Sanitizer) reports of use-after-free in ftrace trigger code paths
Unexplained kernel memory corruption on systems where tracefs is accessible to non-root users or containers

Detection Strategies

Enable KASAN on test and staging kernels to catch use-after-free conditions during trigger churn
Audit which users, containers, or services have CAP_SYS_ADMIN or write access to /sys/kernel/tracing/events/*/trigger
Correlate kernel crash telemetry with recent writes to tracefs trigger interfaces

Monitoring Recommendations

Collect kernel logs centrally and alert on oops or BUG signatures containing ftrace trigger symbols
Monitor process activity that writes to tracefs paths from unprivileged or containerized workloads
Track kernel version and patch state across the fleet to identify unpatched hosts

How to Mitigate CVE-2026-68283

Immediate Actions Required

Apply the upstream kernel patches from commits 79097812153b826fc156a2930ec8a90ed9edf4a2 and b9c8a1400a3bf633f32820d184f3e05fed0f4af7 or the corresponding vendor updates
Restrict access to tracefs and debugfs so only trusted administrators can create event triggers
Reboot systems after patching to ensure the fixed kernel is active

Patch Information

The fix is available in the mainline Linux kernel via the Kernel Git Commit Log and Kernel Git Commit Log. Distribution vendors backport these commits to supported stable kernel branches. Verify your running kernel includes both changes before considering systems remediated.

Workarounds

Unmount or restrict tracefs on production systems that do not require live tracing: mount -o remount,mode=0700 /sys/kernel/tracing
Deny CAP_SYS_ADMIN and tracefs write access to container workloads via seccomp, AppArmor, or SELinux policies
Disable histogram and enable triggers in environments where tracing is not required

bash

# Configuration example: restrict tracefs access to root only
mount -o remount,mode=0700,uid=0,gid=0 /sys/kernel/tracing

# Verify kernel version includes the fix
uname -r

# Audit users with write access to trigger files
find /sys/kernel/tracing/events -name trigger -perm /o+w 2>/dev/null