CVE-2026-72071 tracing/user_events: Fix use-after-free in user_event_mm_dup()
An unprivileged local attacker can trigger a use-after-free in the Linux kernel's user_events tracing subsystem during fork, potentially leading to code execution or privilege escalation.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-72071?
CVE-2026-72071 is a high-severity use after free vulnerability in Linux, published on 15 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
tracing/user_events: Fix use-after-free in user_event_mm_dup()
user_event_mm_dup() walks the parent mm's enabler list locklessly under rcu_read_lock() during fork() (from copy_process()); it does not take event_mutex:
rcu_read_lock(); list_for_each_entry_rcu(enabler, &old_mm->enablers, mm_enablers_link) enabler->event = user_event_get(orig->event);
user_event_enabler_destroy() removes an enabler from that list with list_del_rcu() and then, without waiting for a grace period, drops the enabler's user_event reference with user_event_put() and frees the enabler with kfree(). A reader that loaded the enabler before the list_del_rcu() can still be walking it, which leads to two use-after-frees:
- kfree(enabler) frees the enabler while that reader dereferences enabler->event.
- user_event_put() may drop the last reference to the user_event, which is then freed (via delayed_destroy_user_event() on a work queue), while the same reader does user_event_get(orig->event) on it.
Both are reachable by an unprivileged task that can open user_events_data: one multithreaded process that registers an enabler and then concurrently unregisters it and calls fork() triggers the race. KASAN reports a slab-use-after-free in user_event_mm_dup() during clone(), with a "refcount_t: addition on 0" warning when the user_event is freed.
The enabler use-after-free was found first; the user_event one was reported by XIAO WU, and the earlier enabler-only fix did not address it.
Defer both the user_event_put() and the kfree(enabler) to a work item queued with queue_rcu_work(), so they run only after an RCU grace period, once all readers walking the enabler list have finished. The put must run in process context because user_event_put() takes event_mutex on the last reference, so a work queue is used rather than call_rcu(). The now-unlocked put lets the locked argument of user_event_enabler_destroy() be removed; all callers are updated.
Which versions are affected by CVE-2026-72071?
How do I fix CVE-2026-72071?
Apply the vendor's patch.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2026-72071 being exploited?
There is no known exploitation of CVE-2026-72071 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-72071, DEBIAN-CVE-2026-72071, GHSA-c3qx-9jfj-8c4p, UBUNTU-CVE-2026-72071.