Junglewise Threat Intelligence

CVE-2026-31671: Linux Kernel information leak in xfrm_user build_report

CVE-2026-31671 · Severity: medium · CVSS 5.5 · Published 2026-04-24

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

Executive brief

A security vulnerability has been identified in the Linux kernel's networking subsystem, specifically affecting how it handles IPsec (XFRM) reports. This flaw allows small amounts of sensitive kernel memory to leak to user-level applications because certain internal data structures were not properly cleared before being shared. While this specific bug is primarily noted for causing potential stability issues or minor data exposure, it represents a weakness in how the system protects private kernel information from ordinary users.

Technical details

An information leak vulnerability exists in the Linux kernel's net/xfrm/xfrm_user.c component. The 'xfrm_user_report' structure contains a single-byte 'proto' field followed by an 'xfrm_selector' structure, resulting in three bytes of uninitialized padding. Because this structure is copied to userspace without being zeroed (e.g., via memset), sensitive kernel stack or heap data residing in those padding bytes can be disclosed to local users. The fix involves explicitly zeroing the structure before populating its members. This affects various Linux stable branches and integrated products like Siemens SIMATIC S7-1500 MFP CPUs that utilize the Linux kernel.

Affected products

  • Linux Linux Kernel All versions prior to the April 2026 patches
  • 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

  • 2026-04-06: patched: Initial patch authored by Greg Kroah-Hartman
  • 2026-04-24: advisory: CVE published to NVD
  • 2026-07-14: other: Siemens advisory added to record

References

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