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CVE-2026-23321

5.5 · MEDIUM

In the Linux kernel, the following vulnerability has been resolved: mptcp: pm: in-kernel: always mark signal+subflow endp as used Syzkaller managed to find a combination of actions that was gener…

Published Mar 25, 2026EPSS 0.13%

Overview

CVE-2026-23321 is a medium-severity vulnerability. It was published on March 25, 2026 and has a CVSS 3.1 base score of 5.5 (MEDIUM).

This vulnerability has a CVSS 3.1 base score of 5.5, rated MEDIUM. It requires local or adjacent network access to exploit. Some level of privileges is required for exploitation.

Technical description

In the Linux kernel, the following vulnerability has been resolved:

mptcp: pm: in-kernel: always mark signal+subflow endp as used

Syzkaller managed to find a combination of actions that was generating

this warning:

msk->pm.local_addr_used == 0

WARNING: net/mptcp/pm_kernel.c:1071 at __mark_subflow_endp_available net/mptcp/pm_kernel.c:1071 [inline], CPU#1: syz.2.17/961

WARNING: net/mptcp/pm_kernel.c:1071 at mptcp_nl_remove_subflow_and_signal_addr net/mptcp/pm_kernel.c:1103 [inline], CPU#1: syz.2.17/961

WARNING: net/mptcp/pm_kernel.c:1071 at mptcp_pm_nl_del_addr_doit+0x81d/0x8f0 net/mptcp/pm_kernel.c:1210, CPU#1: syz.2.17/961

Modules linked in:

CPU: 1 UID: 0 PID: 961 Comm: syz.2.17 Not tainted 6.19.0-08368-gfafda3b4b06b #22 PREEMPT(full)

Hardware name: QEMU Ubuntu 25.10 PC v2 (i440FX + PIIX, + 10.1 machine, 1996), BIOS 1.17.0-debian-1.17.0-1build1 04/01/2014

RIP: 0010:__mark_subflow_endp_available net/mptcp/pm_kernel.c:1071 [inline]

RIP: 0010:mptcp_nl_remove_subflow_a

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References

Refgit.kernel.org/stable/c/05799c2f1ca5eb13d65764dda688d02021b65e06Refgit.kernel.org/stable/c/198824ccfa64ffebd918bf99c939bd8170a4a4d8Refgit.kernel.org/stable/c/579a752464a64cb5f9139102f0e6b90a1f595cebRefgit.kernel.org/stable/c/67f34ab318807989b57dfdb0f79e2d4e57018290Refgit.kernel.org/stable/c/a64aa7db39392add5be09dffaedbf1f0ce5554dfRefgit.kernel.org/stable/c/c5c877e140e5f46023a74a51e577ce5edd0a4be7Refcert-portal.siemens.com/productcert/html/ssa-019113.htmlRefcert-portal.siemens.com/productcert/html/ssa-082556.html

How CyberStrike helps

Frequently asked questions

What is CVE-2026-23321?

CVE-2026-23321 is a medium-severity vulnerability. It was published on March 25, 2026 and has a CVSS 3.1 base score of 5.5 (MEDIUM).

How severe is CVE-2026-23321?

This vulnerability has a CVSS 3.1 base score of 5.5, rated MEDIUM. It requires local or adjacent network access to exploit. Some level of privileges is required for exploitation.

How do I fix or remediate CVE-2026-23321?

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2026-23321?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-23321 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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