Linux kernel KEV remediation: verify each CVE against the distribution package and running kernel

What it is

Status as of 25 October 2026. CISA's KEV catalogue includes the following distinct Linux kernel flaws. Re-check each KEV action and your distribution's package status before closing a finding. The Ubuntu CVE-2026-31431 page and CloudLinux's three-CVE advisory used here both show an update dated 12 October 2026.

CVE	Defensive scope	KEV addition
CVE-2026-31431	Copy Fail: cryptographic-interface privilege escalation	1 May 2026
CVE-2026-53362	IPv6 subsystem privilege escalation	27 August 2026
CVE-2026-53266	Out-of-bounds write in bridge filtering	18 September 2026
CVE-2025-39682	Incorrect condition handling in kernel TLS	18 September 2026
CVE-2025-39964	Race condition in the cryptographic socket interface	18 September 2026

Why it matters

These entries are not interchangeable names for one fix. Ubuntu describes Copy Fail as permitting local privilege escalation and possible container escape. CloudLinux documents different affected-product and livepatch coverage for the other three flaws it assesses. Avoid classifying every entry as having identical prerequisites or impact.

A distribution may supply a security fix within its existing kernel family. For the Ubuntu linux source package, Copy Fail is fixed in 6.8.0-117.117 on 24.04 LTS and 5.15.0-179.189 on 22.04 LTS. Those package versions are the relevant examples here; an upstream major-version threshold would discard the distribution's own assessment.

How to apply

• Identify what is running. Record cat /etc/os-release and uname -r. On a packaged Ubuntu installation, use dpkg-query -W "linux-image-$(uname -r)" to identify the active image package. Record its flavour, architecture and repository; cloud, hardware-enablement and vendor kernels need their own advisory rows.
• Build a CVE-by-host matrix. For each listed CVE, retain the distribution's affected, fixed or not-affected determination and the advisory revision. The Ubuntu fixes above apply only to Copy Fail in the named source-package family. They do not establish that the IPv6, bridge, TLS or socket-race findings are closed.
• Install and activate the correct kernel. Use the distribution's supported security-update path, then schedule a reboot into the fixed kernel. Re-run the inventory commands after reboot. Compare package versions using the distribution's version rules, and verify that the intended image actually booted. A newer package remaining on disk is insufficient.
• Treat livepatch as separate evidence. On Ubuntu, inspect canonical-livepatch status; the documented output distinguishes kernel support from patch state. Require the vendor's coverage notice for each applicable CVE and that exact running kernel. For KernelCare deployments, CloudLinux specifies kcarectl --patch-info to inspect CVE coverage; --info is only a summary. Without explicit applicable coverage, retain the kernel-update-and-reboot action.
• Use only scoped interim mitigation. Ubuntu's USN-8226-1, dated 30 April 2026, documents a temporary kmod update blocking algif_aead and requires a reboot. Treat that as a vendor-specific Copy Fail mitigation, not a permanent replacement for a fixed kernel or protection against every cryptographic flaw. Check the current notice before applying or removing any restriction.

Pitfalls

Do not unload cryptographic or networking components merely because another distribution recommends it. CloudLinux specifically warns that module blocking does not disable its built-in interface for CVE-2025-39964. Missing crashes or a successful livepatch check-in cannot prove absence of compromise. If investigation establishes unauthorized privileged changes, preserve evidence and rebuild from trusted media rather than using patch installation as an integrity verdict.