VulnerabilityPublished 18 Oct 2026

CVE-2026-98639: Linux kernel · KVM: riscv: Fix NACL hfence entry update order

Affects Linux kernelSource CVE Database V5

Not known to be exploited · fixed in d6de766d8d26d71b714f548192099112def50a9c : update Linux kernel when convenient.

Data as of 26 Oct 2026, 14:05 UTC

Severity

Medium

Rated Medium by Threat Radar's AI analysis · CVSS not yet scored by NVD

EPSS: 0.1% chance of exploitation in 30 days – higher than 5% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in d6de766d8d26d71b714f548192099112def50a9c, b3d346838ec65fac7fd83f5dbcedd13cadfffddb, 6da466502621381fa88a6684290923d25c559266

Exploitation evidence

Disclosed: evidence found.
CVE published 18 Oct 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade Linux kernel to d6de766d8d26d71b714f548192099112def50a9c, b3d346838ec65fac7fd83f5dbcedd13cadfffddb or 6da466502621381fa88a6684290923d25c559266.

Affected software

Product	Affected	Fixed in
LinuxLinux	Affected ≥ d466c19cead5904d4d5d92adb2b213b411d3b849, < d6de766d8d26d71b714f548192099112def50a9c	Fixed in d6de766d8d26d71b714f548192099112def50a9c
LinuxLinux	Affected ≥ d466c19cead5904d4d5d92adb2b213b411d3b849, < b3d346838ec65fac7fd83f5dbcedd13cadfffddb	Fixed in b3d346838ec65fac7fd83f5dbcedd13cadfffddb
LinuxLinux	Affected ≥ d466c19cead5904d4d5d92adb2b213b411d3b849, < 6da466502621381fa88a6684290923d25c559266	Fixed in 6da466502621381fa88a6684290923d25c559266
LinuxLinux	Affected =6.13	Fixed in–

AI-suggested

A fix is available and has been applied in the Linux kernel commits identified by hashes d6de766d8d26d71b714f548192099112def50a9c, b3d346838ec65fac7fd83f5dbcedd13cadfffddb, and 6da466502621381fa88a6684290923d25c559266. Users should update to a fixed kernel version to remediate this issue.

Description

A vulnerability in the Linux kernel's KVM implementation for RISC-V was fixed by correcting the order of updates to the nested HFENCE entry. The improper update order could cause the SBI implementation or NACL hardware to observe stale page number and count values, leading to incorrect TLB flush ranges.

Impact

Incorrect TLB flush ranges may occur due to the consumer observing stale page number and count values. This could potentially affect memory management correctness in nested virtualization environments on RISC-V platforms using KVM. No known exploits in the wild have been reported.

Summary

CVE-2026-98639 addresses a flaw in the Linux kernel's KVM RISC-V code where the nested HFENCE entry update order did not comply with the SBI v3.0 specification. The vulnerable code wrote the Config word before updating the Page_Number and Page_Count, allowing an external agent to see a pending entry with outdated values. The fix changes the update sequence to write the page number and count first, then the Config word last, using WRITE_ONCE() and smp_wmb() to ensure proper memory ordering and visibility.

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 26 Oct 2026, 10:06 UTC

Technical details

References

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