CVE-2026-43035: Linux kernel information leak in tc_chain_fill_node

CVE-2026-43035 · Severity: medium · CVSS 5.5 · Published 2026-05-01

A vulnerability in the Linux kernel's networking subsystem could allow a local user to access sensitive information from the system's memory. This occurs because certain internal messages were not properly cleared before being sent to user-accessible areas. While this specific flaw primarily impacts system privacy, it could potentially be used to facilitate more complex attacks against the operating system or affected industrial hardware.

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-2026-43035 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-43035 being exploited in the wild.
How severe is CVE-2026-43035?
Medium severity, with a CVSS score of 5.5, published 1 May 2026.
Which products and versions are affected?
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-2026-43035?
A patch was published on 2026-04-11: Patches committed to stable kernel trees Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-43035 attacked?
It is attacked with local access, in an operating system.
Am I affected by CVE-2026-43035?
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

An information leak vulnerability exists in the Linux kernel's net/sched/cls_api.c component due to an uninitialized resource (CWE-908). The function tc_chain_fill_node() fails to initialize the tcm_info field of the tcmsg structure. Because the underlying memory allocation is not zeroed, 4 bytes of kernel heap memory are leaked to userspace when netlink messages are constructed. A local attacker with basic privileges can exploit this to read sensitive kernel memory. The issue has been resolved in multiple stable kernel branches by explicitly zeroing the tcm_info field.

Affected products

  • Linux Linux Kernel
  • 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

  • 2026-03-29: disclosed: Initial patch authored by Yochai Eisenrich
  • 2026-04-11: patched: Patches committed to stable kernel trees
  • 2026-05-01: advisory: CVE published to NVD
  • 2026-07-14: advisory: Siemens updated advisory with affected industrial products

References

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