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

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, Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP, Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP, Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP. Vendors: Linux, 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

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