--- id: CVE-2026-31555 title: |- 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+… summary: |- 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+… severity: medium cvss: 5.5 cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H' cwe: - CWE-825 vendor: linux product: linux_kernel affected: - 'linux_kernel >= 4.4.255, < 4.5' - 'linux_kernel >= 4.9.255, < 4.10' - 'linux_kernel >= 4.14.158, < 4.15' - 'linux_kernel >= 4.19.172, < 4.20' - 'linux_kernel >= 5.4.1, < 5.5' - 'linux_kernel >= 5.5.1, < 5.10.253' - 'linux_kernel >= 5.11, < 5.15.203' - 'linux_kernel >= 5.16, < 6.1.168' - 'linux_kernel >= 6.2, < 6.6.131' - 'linux_kernel >= 6.7, < 6.12.80' - 'linux_kernel >= 6.13, < 6.18.21' - 'linux_kernel >= 6.19, < 6.19.11' - linux_kernel = 5.5 - linux_kernel = 7.0 patched: - linux_kernel 6.19.11 published: '2026-04-24' updated: '2026-10-15' sourceUpdated: '2026-10-15T02:19:11.080' source: NVD sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-31555' references: - url: 'https://git.kernel.org/stable/c/210d36d892de5195e6766c45519dfb1e65f3eb83' label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 - url: 'https://git.kernel.org/stable/c/33095ae3bdde5e5c264d7e88a2f3e7703a26c7aa' label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 - url: 'https://git.kernel.org/stable/c/5e8e06bf8909e79b4acd950cf578cfc2f10bbefa' label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 - url: 'https://git.kernel.org/stable/c/71112e62807d1925dc3ae6188b11f8cfc85aec23' label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 - url: 'https://git.kernel.org/stable/c/7475dfad10a05a5bfadebf5f2499bd61b19ed293' label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 - url: 'https://git.kernel.org/stable/c/92e47ad03e03dbb5515bdf06444bf6b1e147310d' label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 - url: 'https://git.kernel.org/stable/c/de7c0c04ad868f2cee6671b11c0a6d20421af1da' label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 - url: 'https://git.kernel.org/stable/c/e7824ec168d2ac883a213cd1f4d6cc0816002a85' label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 - url: 'https://cert-portal.siemens.com/productcert/html/ssa-019113.html' label: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e - url: 'https://cert-portal.siemens.com/productcert/html/ssa-082556.html' label: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e - url: 'https://cert-portal.siemens.com/productcert/html/ssa-457936.html' label: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e - url: >- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-31555.json - url: 'https://access.redhat.com/security/cve/CVE-2026-31555' - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2461473' - url: 'https://www.cve.org/CVERecord?id=CVE-2026-31555' - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-31555' - url: >- https://lore.kernel.org/linux-cve-announce/2026042456-CVE-2026-31555-ba94@gregkh/T - url: 'https://access.redhat.com/errata/RHSA-2026:51035' tags: - nvd - csaf - vex - red-hat - cve.org epss: 0.00129 epssPercentile: 0.02501 ingestedAt: '2026-09-08T15:33:26.990Z' --- ## Overview 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. ## Affected - `linux_kernel >= 4.4.255, < 4.5` - `linux_kernel >= 4.9.255, < 4.10` - `linux_kernel >= 4.14.158, < 4.15` - `linux_kernel >= 4.19.172, < 4.20` - `linux_kernel >= 5.4.1, < 5.5` - `linux_kernel >= 5.5.1, < 5.10.253` - `linux_kernel >= 5.11, < 5.15.203` - `linux_kernel >= 5.16, < 6.1.168` - `linux_kernel >= 6.2, < 6.6.131` - `linux_kernel >= 6.7, < 6.12.80` - `linux_kernel >= 6.13, < 6.18.21` - `linux_kernel >= 6.19, < 6.19.11` - `linux_kernel = 5.5` - `linux_kernel = 7.0` ## Remediation Upgrade past the affected range: - `linux_kernel 6.19.11` ## Vendor advisories - **RHSA-2026:51035** · Red Hat · fixed in: Red Hat Enterprise Linux AppStream (v. 9), Red Hat Enterprise Linux BaseOS (v. 9), Red Hat Enterprise Linux CodeReady Linux Builder (v. 9), Red Hat Enterprise Linux Real Time for NFV (v. 9), Red Hat Enterprise Linux Real Time (v. 9) · released 2026-08-06 · [advisory](https://access.redhat.com/errata/RHSA-2026:51035) - **Red Hat VEX** · Moderate · affected: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 7, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9 · no fix planned: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 7, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9 · updated 2026-09-15 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-31555.json)