CVE-2026-99082 Linux CVE debrief

Who should care

System administrators and security teams responsible for managing Linux-based systems and KVM-based virtualization infrastructure should assess their exposure to this vulnerability and apply patches or mitigations as necessary.

Why it matters

This vulnerability in the Linux kernel's KVM subsystem could potentially allow a guest to cause unintended behavior, highlighting the need for system administrators and security teams to assess their exposure and apply patches or mitigations.

• Verify and apply patches to prevent potential guest-to-host attacks
• Monitor system logs for exploitation attempts
• Implement additional security controls to prevent similar attacks

Technical summary

The Linux kernel's KVM subsystem is vulnerable to an issue caused by the incorrect use of memslots for the per-vCPU MMIO cache. This can lead to a guest accessing valid RAM as if it were MMIO, potentially causing unintended behavior. The issue was introduced when the SMM address space was added, but the helpers were not converted to use the active memslots. Affected product deployments should review and apply patches to prevent potential guest-to-host attacks. System administrators and security teams should assess their exposure and implement additional security controls to prevent similar attacks.

Defensive priority

High

Recommended defensive actions

• Review and apply the available patches to update the KVM subsystem
• Monitor system logs for potential exploitation attempts
• Implement additional security controls to prevent guest-to-host attacks
• Verify whether affected product deployments exist in managed environments
• Review compensating controls for exposed systems while remediation is scheduled
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented

Evidence notes

The vulnerability is caused by the incorrect use of memslots in the KVM subsystem. The issue was introduced when the SMM address space was added, but the helpers were not converted to use the active memslots. This can lead to a stale MMIO cache entry being used after a memslot update, causing a guest to access valid RAM as if it were MMIO. The CVE Program record and the NVD vulnerability detail page provide additional information about this vulnerability.

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.