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STACKIT-2026-003: Critical Vulnerability in Linux Kernel IPv4 TCP Handling

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Advisory metadata

Section titled “Advisory metadata”
Attribute Value
Advisory ID STACKIT-2026-003
Published date 2026-10-29
Severity High
Affected service STACKIT-managed services / self-managed Linux workloads

Overview

Section titled “Overview”

A race condition in the Linux kernel’s handling of IPv4 TCP connection establishment was disclosed on 2026-10-15 (CVE-2026-98432). The vulnerability exists in all Linux kernel versions since 4.4 and affects IPv4 only; the related IPv6 processing is not affected. The affected code path is reportedly reachable through an MPTCP listener.

Exploitation of this vulnerability allows unauthenticated threat actors to trigger a use-after-free condition in the kernel, which can result in the disclosure of adjacent kernel memory, corruption of kernel memory, or a system crash. A working proof of concept was reported on 2026-10-27; as of 2026-10-29, no exploitation of this vulnerability on STACKIT infrastructure is known. The vulnerability is addressed in the kernel releases 5.10.272, 5.15.223, 6.1.190, 6.6.159, 6.12.113, 6.18.56, 7.2.10, and 7.3.

STACKIT is aware that this vulnerability affects multiple of its managed services. In response to reports that a frontier AI model was able to develop an exploitation path in a controlled lab environment, further actions have been taken to protect STACKIT and its customers. The responsible teams have been notified immediately and are addressing the remediation across the affected services; this bulletin is updated as significant changes or additional information become available. Customers who operate self-managed Linux systems must install the vendor or distribution updates directly. In addition, all customers must review and restrict network access to their Linux systems until patching is complete.

Affected versions

Section titled “Affected versions”

The vulnerability affects the following Linux kernel versions:

  • All Linux kernel versions from 4.4 up to the resolved releases
  • Linux kernel < 5.10.272 (5.10 branch)
  • Linux kernel < 5.15.223 (5.15 branch)
  • Linux kernel < 6.1.190 (6.1 branch)
  • Linux kernel < 6.6.159 (6.6 branch)
  • Linux kernel < 6.12.113 (6.12 branch)
  • Linux kernel < 6.18.56 (6.18 branch)
  • Linux kernel < 7.2.10 (7.2 branch)

Kernel versions that have reached end of life and receive no security updates require migration to a maintained branch.

Identified CVEs

Section titled “Identified CVEs”

The advisory addresses the following Common Vulnerabilities and Exposures (CVEs):

Required actions

Section titled “Required actions”

Self-managed systems

Section titled “Self-managed systems”
  • Inspect all self-managed Linux systems, including virtual machines and embedded Linux components, for affected kernel versions (for example with uname -r).
  • Apply the security updates to upgrade to one of the resolved versions: Linux kernel ≥ 5.10.272, ≥ 5.15.223, ≥ 6.1.190, ≥ 6.6.159, ≥ 6.12.113, ≥ 6.18.56, or ≥ 7.2.10, ≥ 7.3, or apply the corresponding vendor or distribution kernel updates.
  • Verify the installed kernel version against your distribution’s fixed version, as distribution packages include the fix under different version numbers.
  • Restrict network access to self-managed Linux systems to authorized client hosts and internal networks until patching is complete.

STACKIT-managed services

Section titled “STACKIT-managed services”
  • Platform updates: STACKIT initiated platform updates for the affected services to apply kernel security patches across the service infrastructure.
  • For STACKIT Kubernetes Engine (SKE): Flatcar OS preview version 4757.2.2-containerd2.2.10, released on 2026-10-26, ships Linux kernel 6.12.113 and includes the fix for CVE-2026-98432. As a preview version it is not deployed automatically; update the OS version of your worker nodes to this version to obtain the fix.
  • For virtual machines running on STACKIT: review the kernel version used by your systems and update to one of the resolved versions.

References

Section titled “References”

Contact and support

Section titled “Contact and support”

For questions regarding this advisory or assistance with system configuration, contact STACKIT Support:

  • Open a ticket through the STACKIT Help Center.
  • Contact the support team by email at cybersecurity@stackit.cloud.