# CVE-2026-31555: Linux Kernel stale pointer in futex_lock_pi retry path

Source: https://junglewise.ai/threats/cve-2026-31555-linux-kernel-stale-pointer-in-futex-lock-pi-retry-path  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-04-24. Updated: 2026-07-14  
License: CC BY 4.0 with a link back

CVE-2026-31555 · Severity: medium · CVSS 5.5 · Published 2026-04-24

A vulnerability was identified in the Linux kernel's futex subsystem, which manages how different programs coordinate access to shared resources. Under specific conditions where a process is exiting while another tries to lock a resource, the system can encounter a memory error that causes a kernel warning or potential instability. This could be used by a local attacker to cause a system crash or denial-of-service, impacting the availability of the affected machine or industrial controller.

Technologies: [Linux Kernel](https://junglewise.ai/threats/technologies/kernel), [Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP](https://junglewise.ai/threats/technologies/simatic-s7-1500-cpu-1518-4-pn-dp-mfp), [Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP](https://junglewise.ai/threats/technologies/simatic-s7-1500-cpu-1518f-4-pn-dp-mfp), [Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP](https://junglewise.ai/threats/technologies/siplus-s7-1500-cpu-1518-4-pn-dp-mfp). Vendors: [Linux](https://junglewise.ai/threats/vendors/linux), [Siemens](https://junglewise.ai/threats/vendors/siemens).

## Quick answers

**Is CVE-2026-31555 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-31555 being exploited in the wild.

**How severe is CVE-2026-31555?** Medium severity, with a CVSS score of 5.5, published 24 April 2026.

**Which products and versions are affected?** Linux Kernel All versions prior to the fix (including 5.x, 6.x); Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP V3.1.5, V3.1.6; Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP V3.1.5, V3.1.6; Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP V3.1.5, V3.1.6.

**Is there a fix for CVE-2026-31555?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-31555 attacked?** It is attacked with local access, in an operating system.

**Am I affected by CVE-2026-31555?** Check whether you run Linux Kernel, Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP, Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP or one of the others listed at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A vulnerability exists in the Linux kernel futex subsystem due to a stale pointer in the futex_lock_pi() retry path. When futex_lock_pi_atomic() detects an exiting owner, it returns -EBUSY and stores a refcounted task pointer in 'exiting'. If wait_for_owner_exiting() consumes the reference but the operation retries and subsequently returns a different error (like -EAGAIN), the 'exiting' pointer remains populated with a stale value. This stale pointer is then passed back into wait_for_owner_exiting(), triggering a kernel warning (WARN_ON_ONCE) and potential memory corruption or instability. The fix involves explicitly resetting the 'exiting' pointer to NULL at the start of the retry loop.

## Affected products

- Linux Linux Kernel All versions prior to the fix (including 5.x, 6.x)
- Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP V3.1.5, V3.1.6
- Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP V3.1.5, V3.1.6
- Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP V3.1.5, V3.1.6

## Timeline

- 2026-03-25: other: Patch authored by Davidlohr Bueso
- 2026-04-24: disclosed: CVE published

## References

- [https://git.kernel.org/stable/c/210d36d892de5195e6766c45519dfb1e65f3eb83](https://git.kernel.org/stable/c/210d36d892de5195e6766c45519dfb1e65f3eb83)
- [https://git.kernel.org/stable/c/33095ae3bdde5e5c264d7e88a2f3e7703a26c7aa](https://git.kernel.org/stable/c/33095ae3bdde5e5c264d7e88a2f3e7703a26c7aa)
- [https://git.kernel.org/stable/c/5e8e06bf8909e79b4acd950cf578cfc2f10bbefa](https://git.kernel.org/stable/c/5e8e06bf8909e79b4acd950cf578cfc2f10bbefa)
- [https://git.kernel.org/stable/c/71112e62807d1925dc3ae6188b11f8cfc85aec23](https://git.kernel.org/stable/c/71112e62807d1925dc3ae6188b11f8cfc85aec23)
- [https://git.kernel.org/stable/c/7475dfad10a05a5bfadebf5f2499bd61b19ed293](https://git.kernel.org/stable/c/7475dfad10a05a5bfadebf5f2499bd61b19ed293)
- [https://git.kernel.org/stable/c/92e47ad03e03dbb5515bdf06444bf6b1e147310d](https://git.kernel.org/stable/c/92e47ad03e03dbb5515bdf06444bf6b1e147310d)
- [https://git.kernel.org/stable/c/de7c0c04ad868f2cee6671b11c0a6d20421af1da](https://git.kernel.org/stable/c/de7c0c04ad868f2cee6671b11c0a6d20421af1da)

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