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Linux KernelOperating system · Linux

CVE-2026-31555

MEDIUM · 5.5 CVSS v3.1 Published 2026-04-24
Fix available
A fix is available. Upgrade to 4.5 / 4.10 or later.
See remediation →
57/100
Remediation priority · Elevated
Zero-click Patch available

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis

A detailed technical summary for this CVE is being prepared.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Linux KernelOperating system
Affected:>= 4.4.255, < 4.5>= 4.9.255, < 4.10>= 4.14.158, < 4.15>= 4.19.172, < 4.20>= 5.4.1, < 5.5>= 5.5.1, < 5.10.253>= 5.11, < 5.15.203>= 5.16, < 6.1.168>= 6.2, < 6.6.131>= 6.7, < 6.12.80>= 6.13, < 6.18.21>= 6.19, < 6.19.11

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Local
Complexity
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 4.5 / 4.10 / 4.15 or later
Fixed in 4.54.104.15
Vendor patch git.kernel.org →
Recommended fix High confidence

4.5, 4.10, 4.15, or 4.20 (depending on which branch you are on)

  1. Identify the currently running Linux kernel version using `uname -r`
  2. Determine which version range your current kernel falls into: 4.4.255-4.4.x, 4.9.255-4.9.x, 4.14.158-4.14.x, or 4.19.172-4.19.x
  3. Upgrade the kernel to the next stable release in that branch: 4.5.x, 4.10.x, 4.15.x, or 4.20.x respectively
  4. Reboot the system to load the patched kernel
  5. Verify the fix is applied by checking the kernel version with `uname -r`
Caveat Kernel upgrades may require rebuilding out-of-tree kernel modules; ensure driver compatibility before upgrading

Generated from the published advisory — verify against the referenced sources before acting.

We can perform the upgrade in your staging environment and verify nothing breaks — typical engagement from $1,600. Get the upgrade done

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-31555 in production — separate from our analysis above.

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