CVE-2025-39823

Guest-to-host disclosure via speculative array indexing

Published Sep 16, 2025 · Updated Sep 16, 2025

Information disclosure in Linux KVM x86 allows guest OS users to expose host data through speculative execution of array accesses. The local APIC and x86 code bounds-check guest-controlled min and dest_id values but then index arrays without clamping speculation, allowing transient out-of-bounds access. Guest OS users able to run code in a KVM guest can target host-side data indirectly; the public record does not establish direct reads, writes, or code execution.

CVSS severity7.8
High
EPSS probability0.18%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Information disclosure in Linux KVM x86 allows guest OS users to expose host data through speculative execution of array accesses. The local APIC and x86 code bounds-check guest-controlled min and dest_id values but then index arrays without clamping speculation, allowing transient out-of-bounds access. Guest OS users able to run code in a KVM guest can target host-side data indirectly; the public record does not establish direct reads, writes, or code execution.

The record

CVE
CVE-2025-39823
Published
Sep 16, 2025
Updated
Sep 16, 2025
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-129
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Sep 16, 2025CVE publishedPublication date reported by the CVE source.
  2. Sep 16, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=4180bf1b655a791a0a6ef93a2ffffc762722c782 <31a0ad2f60cb4816e06218b63e695eb72ce74974
  2. Affected versionversion=4180bf1b655a791a0a6ef93a2ffffc762722c782 <33e974c2d5a82b2f9d9ba0ad9cbaabc1c8e3985f
  3. Affected versionversion=4180bf1b655a791a0a6ef93a2ffffc762722c782 <67a05679621b7f721bdba37a5d18665d3aceb695
  4. Affected versionversion=4180bf1b655a791a0a6ef93a2ffffc762722c782 <72777fc31aa7ab2ce00f44bfa3929c6eabbeaf48
  5. Affected versionversion=4180bf1b655a791a0a6ef93a2ffffc762722c782 <c87bd4dd43a624109c3cc42d843138378a7f4548
  6. Affected versionversion=4180bf1b655a791a0a6ef93a2ffffc762722c782 <d51e381beed5e2f50f85f49f6c90e023754efa12
  7. Affected versionversion=4180bf1b655a791a0a6ef93a2ffffc762722c782 <f49161646e03d107ce81a99c6ca5da682fe5fb69
  8. Affected versionversion=4180bf1b655a791a0a6ef93a2ffffc762722c782 <f57a4bd8d6cb5af05b8ac1be9098e249034639fb
  9. Affected versionversion=4.19

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=4180bf1b655a791a0a6ef93a2ffffc762722c782 <31a0ad2f60cb4816e06218b63e695eb72ce74974; version=4180bf1b655a791a0a6ef93a2ffffc762722c782 <33e974c2d5a82b2f9d9ba0ad9cbaabc1c8e3985f; version=4180bf1b655a791a0a6ef93a2ffffc762722c782 <67a05679621b7f721bdba37a5d18665d3aceb695; version=4180bf1b655a791a0a6ef93a2ffffc762722c782 <72777fc31aa7ab2ce00f44bfa3929c6eabbeaf48; version=4180bf1b655a791a0a6ef93a2ffffc762722c782 <c87bd4dd43a624109c3cc42d843138378a7f4548; version=4180bf1b655a791a0a6ef93a2ffffc762722c782 <d51e381beed5e2f50f85f49f6c90e023754efa12; version=4180bf1b655a791a0a6ef93a2ffffc762722c782 <f49161646e03d107ce81a99c6ca5da682fe5fb69; version=4180bf1b655a791a0a6ef93a2ffffc762722c782 <f57a4bd8d6cb5af05b8ac1be9098e249034639fb; version=4.19

Published CVSS scores

7.8NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-129Improper Validation of Array Index

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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