# CVE-2026-31680: Linux Kernel use-after-free in IPv6 flowlabel

Source: https://junglewise.ai/threats/cve-2026-31680-linux-kernel-use-after-free-in-ipv6-flowlabel  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-04-25. Updated: 2026-07-14  
License: CC BY 4.0 with a link back

CVE-2026-31680 · Severity: high · CVSS 7.8 · Published 2026-04-25

A vulnerability in the Linux kernel's networking component could allow a local user to crash the system. The issue occurs when the system attempts to read network flow information while that information is simultaneously being deleted. This can lead to a system instability or a complete crash, potentially disrupting operations or services running on the affected machine.

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). Vendors: [Linux](https://junglewise.ai/threats/vendors/linux), [Siemens](https://junglewise.ai/threats/vendors/siemens).

## Quick answers

**Is CVE-2026-31680 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-31680 being exploited in the wild.

**How severe is CVE-2026-31680?** High severity, with a CVSS score of 7.8, published 25 April 2026.

**Which products and versions are affected?** Linux Kernel Fixed in 6.14, 6.13, 6.12, 6.11, 6.6, 6.1, 5.15, 5.10, 5.4, 4.19; 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.

**Is there a fix for CVE-2026-31680?** A patch was published on 2026-04-18: Patched in various stable kernel branches Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-31680 attacked?** It is attacked with local access, in an operating system.

**Am I affected by CVE-2026-31680?** Check whether you run Linux Kernel, Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP or Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP 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 use-after-free vulnerability exists in net/ipv6/ip6_flowlabel.c due to a race condition between flowlabel release and RCU-protected readers. The function fl_release() prematurely frees 'fl->opt' for exclusive flowlabels when the user count drops to zero, even though the parent 'struct ip6_flowlabel' remains visible in the global hash table until garbage collection. A concurrent reader of /proc/net/ip6_flowlabel (via ip6fl_seq_show) can dereference this freed memory, resulting in a kernel oops or crash. The fix defers the freeing of the option block until the final RCU teardown in fl_free_rcu(). This affects various Linux kernel versions and downstream products like Siemens SIMATIC S7-1500 CPUs.

## Affected products

- Linux Linux Kernel Fixed in 6.14, 6.13, 6.12, 6.11, 6.6, 6.1, 5.15, 5.10, 5.4, 4.19
- 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

## Timeline

- 2026-04-25: disclosed
- 2026-04-18: patched: Patched in various stable kernel branches

## References

- [https://git.kernel.org/stable/c/3c54b66c83fb8fcbde8e6a7bf90b65856e39f827](https://git.kernel.org/stable/c/3c54b66c83fb8fcbde8e6a7bf90b65856e39f827)
- [https://git.kernel.org/stable/c/414726b69921fe6355ae453f5b35e68dd078342a](https://git.kernel.org/stable/c/414726b69921fe6355ae453f5b35e68dd078342a)
- [https://git.kernel.org/stable/c/4b6798024f7b2d535f3db1002c760143cdbd1bd3](https://git.kernel.org/stable/c/4b6798024f7b2d535f3db1002c760143cdbd1bd3)
- [https://git.kernel.org/stable/c/572ce62778519a7d4d1c15f55dd2e45a474133c4](https://git.kernel.org/stable/c/572ce62778519a7d4d1c15f55dd2e45a474133c4)
- [https://git.kernel.org/stable/c/5a6b15f861b7c1304949e3350d23490a5fe429fd](https://git.kernel.org/stable/c/5a6b15f861b7c1304949e3350d23490a5fe429fd)
- [https://git.kernel.org/stable/c/6c7fbdb8ffde6413640de7cfbd7c976c353e89f8](https://git.kernel.org/stable/c/6c7fbdb8ffde6413640de7cfbd7c976c353e89f8)
- [https://git.kernel.org/stable/c/8027964931785cb73d520ac70a342a3dc16c249b](https://git.kernel.org/stable/c/8027964931785cb73d520ac70a342a3dc16c249b)

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