# CVE-2026-31496: Linux Kernel information leak in netfilter nf_conntrack_expect

Source: https://junglewise.ai/threats/cve-2026-31496-linux-kernel-information-leak-in-netfilter-nf-conntrack-expect  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-04-22. Updated: 2026-07-14  
License: CC BY 4.0 with a link back

CVE-2026-31496 · Severity: medium · CVSS 5.5 · Published 2026-04-22

A vulnerability in the Linux kernel's networking subsystem could allow a local user to view connection tracking information belonging to other isolated network environments (namespaces). This component is responsible for managing how the system tracks active network connections. While primarily a privacy and isolation issue, it could be used by an attacker to gain insights into the network activity of other users or containers on the same physical host.

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-2026-31496 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-31496 being exploited in the wild.

**How severe is CVE-2026-31496?** Medium severity, with a CVSS score of 5.5, published 22 April 2026.

**Which products and versions are affected?** Linux Kernel 9b03f38d0487 to 3db5647984de; 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-2026-31496?** 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-2026-31496 attacked?** It is attacked with local access, in an operating system.

**Am I affected by CVE-2026-31496?** 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 in nf_conntrack_expect.c within the Linux kernel's netfilter subsystem allowed the dumping of connection tracking expectations from other network namespaces via the /proc interface. The root cause was a missing namespace check in the exp_seq_show function, which failed to verify if the expectation entry belonged to the current sequence file's namespace. A local attacker with low privileges could exploit this to leak network state information across namespace boundaries. The issue has been resolved by adding a net_eq check to skip expectations that do not reside in the caller's namespace. Patches are available in various stable kernel branches.

## Affected products

- Linux Linux Kernel 9b03f38d0487 to 3db5647984de
- 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
- 2026-04-22: disclosed: CVE published

## References

- [https://git.kernel.org/stable/c/168145c87444619e3e649322bbe7719ecd00d411](https://git.kernel.org/stable/c/168145c87444619e3e649322bbe7719ecd00d411)
- [https://git.kernel.org/stable/c/2028405ea6987b4448784e439413202cfe19f43f](https://git.kernel.org/stable/c/2028405ea6987b4448784e439413202cfe19f43f)
- [https://git.kernel.org/stable/c/3265ad619987cb551edaf797ed056d80ac450225](https://git.kernel.org/stable/c/3265ad619987cb551edaf797ed056d80ac450225)
- [https://git.kernel.org/stable/c/3db5647984de03d9cae0dcddb509b058351f0ee4](https://git.kernel.org/stable/c/3db5647984de03d9cae0dcddb509b058351f0ee4)
- [https://git.kernel.org/stable/c/9ca8c7452493d915f9bbf2f39331e6c583d07a23](https://git.kernel.org/stable/c/9ca8c7452493d915f9bbf2f39331e6c583d07a23)
- [https://git.kernel.org/stable/c/dcfcd95b3ae7683e8ae55c92284b3430ce614bc7](https://git.kernel.org/stable/c/dcfcd95b3ae7683e8ae55c92284b3430ce614bc7)
- [https://cert-portal.siemens.com/productcert/html/ssa-019113.html](https://cert-portal.siemens.com/productcert/html/ssa-019113.html)

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