CVE-2026-31518: Linux Kernel memory leak in ESP over TCP with async crypto

CVE-2026-31518 · Severity: medium · CVSS 5.5 · Published 2026-04-22

A memory management vulnerability has been identified in the Linux kernel's networking component, specifically affecting systems using IPsec (ESP) over TCP with asynchronous encryption. When the network transmission queue becomes full, the system fails to properly release memory associated with network packets. This can lead to a memory leak that eventually causes system instability or a crash, resulting in a denial of service.

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-2026-31518 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-31518 being exploited in the wild.
How severe is CVE-2026-31518?
Medium severity, with a CVSS score of 5.5, published 22 April 2026.
Which products and versions are affected?
Linux Kernel Fixed in 6.1.85, 6.6.26, 6.8.5, and other stable branches; affects versions with espintcp support; 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-2026-31518?
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-2026-31518 attacked?
It is attacked with local access, in an operating system.
Am I affected by CVE-2026-31518?
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 memory leak (CWE-401) exists in the Linux kernel's ESP (Encapsulating Security Payload) implementation within net/ipv4/esp4.c and net/ipv6/esp6.c. The vulnerability occurs when using TCP encapsulation for ESP (espintcp) combined with asynchronous cryptographic operations. When the transmit (TX) queue is full, the function esp_output_tail_tcp returns an error; however, unlike the synchronous crypto path where the XFRM output code handles packet disposal, the asynchronous path (esp_output_done) fails to free the socket buffer (skb). A local attacker could potentially exploit this to exhaust system memory, leading to a denial of service. The issue has been resolved by ensuring kfree_skb is called when esp_output_tail_tcp returns an error in the async path.

Affected products

  • Linux Linux Kernel Fixed in 6.1.85, 6.6.26, 6.8.5, and other stable branches; affects versions with espintcp support
  • 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

  • 2026-02-24: disclosed: Initial patch authored by Sabrina Dubroca
  • 2026-04-22: advisory: NVD publication date
  • 2026-07-14: other: Siemens advisory enrichment added to CVE record

References

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