CVE-2026-53163 locking/rtmutex: Skip remove_waiter() when waiter is not enqueued
A null pointer dereference in the Linux kernel's rtmutex locking mechanism allows local attackers to cause a system crash via futex operations.
- 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-2026-53163?
CVE-2026-53163 is a medium-severity vulnerability in Linux kernel, published on 25 Jun 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:
locking/rtmutex: Skip remove_waiter() when waiter is not enqueued
syzbot triggered the following splat in remove_waiter() via FUTEX_CMP_REQUEUE_PI:
KASAN: null-ptr-deref in range [0x0000000000000a88-0x0000000000000a8f] class_raw_spinlock_constructor remove_waiter+0x159/0x1200 kernel/locking/rtmutex.c:1561 rt_mutex_start_proxy_lock+0x103/0x120 futex_requeue+0x10e4/0x20d0 __x64_sys_futex+0x34f/0x4d0
task_blocks_on_rt_mutex() does not arm the waiter upon deadlock detection, leaving waiter->task nil, where 3bfdc63936dd ("rtmutex: Use waiter::task instead of current in remove_waiter()") made this fatal.
Furthermore, rt_mutex_start_proxy_lock() should not be calling into remove_waiter() upon a successfully grabbing the rtmutex. 1a1fb985f2e2 ("futex: Handle early deadlock return correctly"), moved the remove_waiter() out of __rt_mutex_start_proxy_lock() (where 'ret' was only ever 0 or < 0) into the wrapper. Tighten this check to account for try_to_take_rt_mutex().
Weakness: CWE-476
Which versions are affected by CVE-2026-53163?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-53163?
Apply the vendor's patch.
Is CVE-2026-53163 being exploited?
There is no known exploitation of CVE-2026-53163 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as AZL-90620, BELL-CVE-2026-53163, DEBIAN-CVE-2026-53163, GHSA-4w7w-2mrj-36vw, ROOT-OS-DEBIAN-12-CVE-2026-53163, ROOT-OS-DEBIAN-13-CVE-2026-53163 and 2 more.