CVE-2026-31555
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Vulnerability report for CVE-2026-31555, including description, CVSS score, EPSS score, affected products, exploitability, helpful resources, and attack-flow context.
Publication date: 2026-04-24
Last updated on: 2026-04-27
Assigner: kernel.org
Description
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)
put_task_struct(); // drops ref
// exiting still points to owner
goto retry;
futex_lock_pi_atomic()
lock_pi_update_atomic()
cmpxchg(uaddr)
*uaddr ^= WAITERS // whatever
// value changed
return -EAGAIN;
wait_for_owner_exiting(-EAGAIN, exiting) // stale
WARN_ON_ONCE(exiting)
Fix this by resetting upon retry, essentially aligning it with requeue_pi.
CVSS Scores
EPSS Scores
| Probability: | |
| Percentile: |
Meta Information
Affected Vendors & Products
| Vendor | Product | Version / Range |
|---|---|---|
| linux | linux_kernel | 5.5 |
| linux | linux_kernel | 7.0 |
| linux | linux_kernel | 7.0 |
| linux | linux_kernel | 7.0 |
| linux | linux_kernel | 7.0 |
| linux | linux_kernel | 7.0 |
| linux | linux_kernel | 7.0 |
| linux | linux_kernel | 7.0 |
| linux | linux_kernel | From 5.11 (inc) to 5.15.203 (exc) |
| linux | linux_kernel | From 5.16 (inc) to 6.1.168 (exc) |
| linux | linux_kernel | From 6.13 (inc) to 6.18.21 (exc) |
| linux | linux_kernel | From 6.19 (inc) to 6.19.11 (exc) |
| linux | linux_kernel | From 6.2 (inc) to 6.6.131 (exc) |
| linux | linux_kernel | From 6.7 (inc) to 6.12.80 (exc) |
| linux | linux_kernel | From 5.5.1 (inc) to 5.10.253 (exc) |
| linux | linux_kernel | From 4.14.158 (inc) to 4.15 (exc) |
| linux | linux_kernel | From 4.19.172 (inc) to 4.20 (exc) |
| linux | linux_kernel | From 4.4.255 (inc) to 4.5 (exc) |
| linux | linux_kernel | From 4.9.255 (inc) to 4.10 (exc) |
| linux | linux_kernel | From 5.4.1 (inc) to 5.5 (exc) |
Helpful Resources
Exploitability
CWE
KEV
| CWE ID | Description |
|---|---|
| CWE-UNKNOWN |
