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VulnerabilityPublished Updated

CVE-2025-39823: Linux kernel · KVM: x86: use array_index_nospec with indices that come from guest

Affects Linux kernelSource CVE Database V5

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Not known to be exploited · fixed in f49161646e03d107ce81a99c6ca5da682fe5fb69 : update Linux kernel when convenient.

Data as of 5 Nov 2026, 21:35 UTC

Severity
Medium

Rated Medium by Threat Radar's AI analysis · No CVSS score from NVD or the CNA

Thin evidence

One scorer or none
CISA SSVC
Exploitation
No evidence of active exploitation and no public proof of concept
Automatable
Attackers cannot reliably automate steps 1–4 of the kill chain
Technical impact
Limited control over the software or limited information exposure

CISA SSVC assessment, 2026-11-05.

Patch
Available – fixed in f49161646e03d107ce81a99c6ca5da682fe5fb69, f57a4bd8d6cb5af05b8ac1be9098e249034639fb, d51e381beed5e2f50f85f49f6c90e023754efa12 +5

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 16 Sep 2025

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq 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 5 Nov 2026.

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

ProductAffectedFixed in
LinuxLinuxAffected
  • ≥ 4180bf1b655a791a0a6ef93a2ffffc762722c782, < f49161646e03d107ce81a99c6ca5da682fe5fb69
Fixed in
  • f49161646e03d107ce81a99c6ca5da682fe5fb69
LinuxLinuxAffected
  • ≥ 4180bf1b655a791a0a6ef93a2ffffc762722c782, < f57a4bd8d6cb5af05b8ac1be9098e249034639fb
Fixed in
  • f57a4bd8d6cb5af05b8ac1be9098e249034639fb
LinuxLinuxAffected
  • ≥ 4180bf1b655a791a0a6ef93a2ffffc762722c782, < d51e381beed5e2f50f85f49f6c90e023754efa12
Fixed in
  • d51e381beed5e2f50f85f49f6c90e023754efa12
LinuxLinuxAffected
  • ≥ 4180bf1b655a791a0a6ef93a2ffffc762722c782, < c87bd4dd43a624109c3cc42d843138378a7f4548
Fixed in
  • c87bd4dd43a624109c3cc42d843138378a7f4548
LinuxLinuxAffected
  • ≥ 4180bf1b655a791a0a6ef93a2ffffc762722c782, < 72777fc31aa7ab2ce00f44bfa3929c6eabbeaf48
Fixed in
  • 72777fc31aa7ab2ce00f44bfa3929c6eabbeaf48
LinuxLinuxAffected
  • ≥ 4180bf1b655a791a0a6ef93a2ffffc762722c782, < 67a05679621b7f721bdba37a5d18665d3aceb695
Fixed in
  • 67a05679621b7f721bdba37a5d18665d3aceb695

AI-suggested

A fix is available and has been applied in Linux kernel version 4.19. Users should update to the fixed kernel versions containing the referenced commits to mitigate this vulnerability.

Description

A vulnerability in the Linux kernel's KVM x86 component involves improper handling of guest-controlled indices. The flaw was addressed by applying array_index_nospec() to clamp these indices after bounds checks, mitigating speculative execution side-channel risks.

References

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