CVE-2026-31555

Technical Description

In the Linux kernel, the following vulnerability has been resolved:

futex: Clear stale exiting pointer in futex_lock_pi() retry path

Fuzzying/stressing futexes triggered:

WARNING: kernel/futex/core.c:825 at wait_for_owner_exiting+0x7a/0x80, CPU#11: futex_lock_pi_s/524

When futex_lock_pi_atomic() sees the owner is exiting, it returns -EBUSY

and stores a refcounted task pointer in 'exiting'.

After wait_for_owner_exiting() consumes that reference, the local pointer

is never reset to nil. Upon a retry, if futex_lock_pi_atomic() returns a

different error, the bogus pointer is passed to wait_for_owner_exiting().

CPU0 CPU1 CPU2

futex_lock_pi(uaddr)

// acquires the PI futex

exit()

futex_cleanup_begin()

futex_state = EXITING;

futex_lock_pi(uaddr)

futex_lock_pi_atomic()

attach_to_pi_owner()

// observes EXITING

*exiting = owner; // takes ref

return -EBUSY

wait_for_owner_exiting(-EBUSY, owner)

pu

Remediation

Check the references section for vendor advisories and patches from linux. Update linux_kernel to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

Affected Products

References