CVE-2026-43240 Linux CVE debrief

Who should care

Linux kernel maintainers, distro security teams, operators using kexec-based reboots, and environments that rely on IMA measurement continuity for attestation or compliance should prioritize this issue, especially on systems that use memory-limiting boot parameters.

Technical summary

NVD describes CVE-2026-43240 as an x86 kexec sanity-check problem in the Linux kernel. When booting a second-stage kernel via kexec with a constrained memory map, the previous kernel’s carried-over IMA kexec buffer can point to a physical range that is no longer backed by RAM. The restore path can then fault in ima_restore_measurement_list(), producing a kernel panic. The issue affects availability only in the supplied CVSS vector, and the published fix adds a range sanity check on x86 similar to checks already used by other architectures, validating the buffer against memory bounds before restoration.

Defensive priority

Medium. The CVSS score is 5.5 (MEDIUM), but the operational impact can be high for systems that depend on uninterrupted booting or attestation workflows.

Recommended defensive actions

• Apply the upstream/stable Linux kernel fixes referenced by the official patch links.
• Upgrade to a vendor kernel version that includes the CVE-2026-43240 backport for your branch.
• Review any systems that use kexec together with IMA and memory-limiting boot parameters such as mem=<size>.
• Test reboot and attestation workflows after patching to confirm the IMA measurement list still restores correctly.
• If patching is delayed, assess whether kexec-based reboots can be temporarily avoided on affected x86 systems.
• Monitor distro security advisories for the specific fixed kernel builds in your supported release train.

Evidence notes

The supplied NVD record marks the issue as analyzed and provides a CVSS vector of CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H. The description states that the problem occurs when a kexec-booted second-stage kernel uses a limiting command line such as mem=<size>, causing the previous kernel’s IMA measurement list to fall outside truncated RAM and trigger a page fault/panic. NVD lists Linux kernel version ranges affected and links to official kernel patch commits. No exploit details beyond the boot-time fault condition are included.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.