CVE-2026-31416: 
Linux Kernel vulnerability analysis and mitigation

CVE-2026-31416 is a vulnerability in the Linux kernel's netfilter nfnetlink_log module where NLMSG_DONE fails to properly account for the netlink header size — only the attribute size is considered — resulting in malformed message length calculations. It affects Linux kernel versions from 3.18 up through multiple stable branches, with fixed versions including 5.10.253, 5.15.203, 6.1.168, 6.6.134, 6.12.81, 6.18.22, 6.19.12, and 7.0. The vulnerability was published on April 13, 2026, and has a CVSS v3.1 base score of 5.5 (Medium), exploitable locally with low privileges (GitHub Advisory, Feedly).

The root cause is an off-by-one-style size accounting error (CWE-131: Incorrect Calculation of Buffer Size) in the nfnetlink_log subsystem of the Linux kernel's netfilter framework. When constructing a NLMSG_DONE message, the code accounts only for the netlink attribute payload size and omits the fixed-size netlink message header (struct nlmsghdr), causing the computed message length to be smaller than the actual message. This is described as a follow-up to a prior bug fix that was itself incomplete. The flaw is locally exploitable by a low-privileged user and requires no user interaction (GitHub Advisory, Feedly).

Exploitation of this vulnerability results in kernel WARN splat messages and the subsequent dropping of netlink messages by the kernel, impacting availability of the netfilter logging subsystem. There is no confidentiality or integrity impact. The primary consequence is degraded visibility into network filtering events, which could impair security monitoring tools and intrusion detection systems that rely on netlink log messages from netfilter (GitHub Advisory, Feedly).

There is no known public proof-of-concept exploit and no evidence of in-the-wild exploitation as of the time of this report. The EPSS score is approximately 0.024% (0.000240), indicating a very low probability of exploitation in the near term. The vulnerability is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog. No threat actor attribution has been reported (GitHub Advisory, Feedly).

• Logs: Kernel log entries containing WARN splat messages originating from the nfnetlink_log or netfilter subsystem, particularly referencing message size or NLMSG_DONE handling.
• System Behavior: Unexpected drops of netlink messages from the netfilter logging subsystem; security monitoring tools relying on nfnetlink_log reporting gaps or missing log entries.

Update the Linux kernel to a patched version. Fixed releases include 5.10.253, 5.15.203, 6.1.168, 6.6.134, 6.12.81, 6.18.22, 6.19.12, and 7.0. Patches are available via the stable kernel git repository across multiple commits. Distributions including Amazon Linux 2023, SUSE, and Debian have issued security updates incorporating these fixes. No configuration-based workaround is available; upgrading is the recommended remediation (GitHub Advisory, Amazon Linux Advisory, SUSE Advisory).