CVE-2026-53163
MediumCVSS 5.5Exploitation Probability (EPSS)
Low risk3th percentile — higher than 3% of all known CVEs
Summary
A vulnerability was found in the Linux kernel's rtmutex locking mechanism, where remove_waiter() can be called for a non-enqueued waiter, leading to a NULL pointer dereference. The issue occurs during FUTEX_CMP_REQUEUE_PI operations when the waiter is not properly registered in the wait queue.
Risk Assessment
An attacker could exploit this vulnerability to cause a kernel panic or potentially escalate privileges by manipulating futex operations, threatening system stability and security.
Recommendation
Immediately update the Linux kernel to a version containing the fix (commit that removes the unnecessary remove_waiter() call in rt_mutex_start_proxy_lock()). Check for the patch in your distribution.
Original NVD description (English source)
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().