CVE-2025-39823: Linux kernel · KVM: x86: use array_index_nospec with indices that come from guest
Affects Linux kernelSource CVE Database V5
Not known to be exploited · fixed in f49161646e03d107ce81a99c6ca5da682fe5fb69 : update Linux kernel when convenient.
Data as of 5 Nov 2026, 21:35 UTC
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
Disclosed: evidence found.
CVE published 16 Sep 2025
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: 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 5 Nov 2026.
What to do
Upgrade to a fixed release listed under Affected software.
Affected software
| Product | Affected | Fixed in |
|---|---|---|
| LinuxLinux | Affected
| Fixed in
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| LinuxLinux | Affected
| Fixed in
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| LinuxLinux | Affected
| Fixed in
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| LinuxLinux | Affected
| Fixed in
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| LinuxLinux | Affected
| Fixed in
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| LinuxLinux | Affected
| Fixed in
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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
- git.kernel.org/stable/c/72777fc31aa7ab2ce00f44bfa3929c6eabbeaf48 (opens in a new tab)
- git.kernel.org/stable/c/31a0ad2f60cb4816e06218b63e695eb72ce74974 (opens in a new tab)
- git.kernel.org/stable/c/d51e381beed5e2f50f85f49f6c90e023754efa12 (opens in a new tab)
- git.kernel.org/stable/c/33e974c2d5a82b2f9d9ba0ad9cbaabc1c8e3985f (opens in a new tab)
- git.kernel.org/stable/c/f49161646e03d107ce81a99c6ca5da682fe5fb69 (opens in a new tab)
- git.kernel.org/stable/c/67a05679621b7f721bdba37a5d18665d3aceb695 (opens in a new tab)
- git.kernel.org/stable/c/f57a4bd8d6cb5af05b8ac1be9098e249034639fb (opens in a new tab)
- git.kernel.org/stable/c/c87bd4dd43a624109c3cc42d843138378a7f4548 (opens in a new tab)
- lists.debian.org/debian-lts-announce/2025/10/msg00008.html (opens in a new tab)
- lists.debian.org/debian-lts-announce/2025/10/msg00007.html (opens in a new tab)
- cert-portal.siemens.com/productcert/html/ssa-032379.html (opens in a new tab)