CVE-2026-43040: Linux Kernel information leak in IPv6 ndisc nduseroptmsg

CVE-2026-43040 · Severity: high · CVSS 7.1 · Published 2026-05-01

A vulnerability in the Linux kernel's networking component could allow a local user to view sensitive information stored in the system's memory. This occurs because certain internal data structures used for IPv6 networking do not properly clear old data before sharing it with other parts of the system. An attacker could exploit this to gain insights into kernel operations or bypass security protections, potentially impacting the confidentiality of system data.

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-2026-43040 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-43040 being exploited in the wild.
How severe is CVE-2026-43040?
High severity, with a CVSS score of 7.1, published 1 May 2026.
Which products and versions are affected?
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.
Is there a fix for CVE-2026-43040?
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-2026-43040 attacked?
It is attacked with local access, in an operating system.
Am I affected by CVE-2026-43040?
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 kernel information leak exists in net/ipv6/ndisc.c within the ndisc_ra_useropt function. When the kernel processes IPv6 Router Advertisements (RA) containing user options, it constructs an RTM_NEWNDUSEROPT netlink message using the nduseroptmsg structure. This structure contains three padding fields (nduseropt_pad1, nduseropt_pad2, and nduseropt_pad3) that were not explicitly initialized to zero. Consequently, uninitialized kernel stack or heap memory could be leaked to userspace via netlink. An attacker with local access can monitor these netlink messages to extract sensitive kernel data. The vulnerability has been addressed by explicitly zeroing these padding fields in various stable kernel branches.

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

  • 2026-03-25: other: Patch authored by Yochai Eisenrich
  • 2026-05-01: disclosed: CVE published
  • 2026-07-14: other: Siemens advisory data added to record

References

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