CVE-2026-98639 Linux CVE debrief

Who should care

Linux KVM RISC-V deployment administrators and security teams should assess exposure and apply patches. The vulnerability affects Linux KVM RISC-V deployments, and administrators and security teams should verify patch implementation to ensure fix effectiveness. The fix updates the Page_Number and Page_Count words before the Config word.

Why it matters

A vulnerability in the Linux kernel's KVM implementation for RISC-V could lead to incorrect TLB flush ranges. Assess exposure and apply patches.

• Incorrect TLB flush ranges could lead to data integrity issues
• Verify patch implementation to ensure fix effectiveness

Technical summary

The Linux kernel's KVM implementation for RISC-V had an issue with the ordering of updates to nested HFENCE entries. This could result in incorrect TLB flush ranges. The fix updates the Page_Number and Page_Count words before the Config word. The SBI v3.0 specification requires a specific ordering of updates to nested HFENCE entries. The vulnerability affects Linux KVM RISC-V deployments, and administrators should assess exposure and apply patches. The fix ensures that the Page_Number and Page_Count words are updated before the Config word.

Defensive priority

Assess exposure and apply patches for Linux KVM RISC-V deployments.

Recommended defensive actions

• Assess exposure of Linux KVM RISC-V deployments
• Apply patches from Linux kernel developers
• Verify fix implementation
• Review compensating controls for exposed systems while remediation is scheduled and verified
• 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
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up

Evidence notes

The CVE record and NVD entry provide details on the vulnerability. Linux kernel developers have addressed the issue. The fix updates the Page_Number and Page_Count words before the Config word. Assess exposure and apply patches for Linux KVM RISC-V deployments. Verify patch implementation to ensure fix effectiveness. The SBI v3.0 specification (section 15.1.2) requires a nested HFENCE entry to be populated as follows: 1) find an unused entry with Config.Pending == 0 2) update the Page_Number and Page_Count words 3) update the Config

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.