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NVD / CVE Program· CNA Linux

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

Noroxi assessment

Priority: Monitor (action score 31/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.18% (FIRST EPSS).
  • Someone with local access to the system can trigger it. A low-privileged account is enough. No user action is required. No special conditions are required; it is repeatable.
  • Fixed version: Linux Linux 31a0ad2f60cb4816e06218b63e695eb72ce74974, 33e974c2d5a82b2f9d9ba0ad9cbaabc1c8e3985f, 67a05679621b7f721bdba37a5d18665d3aceb695; azl3 kernel 6.6.96.2-2 on Azure Linux 3.0 6.6.104.2-1; cbl2 kernel 5.15.186.1-1 on CBL Mariner 2.0 5.15.200.1-1.

Low priority for now. Upgrade to Linux Linux 31a0ad2f60cb4816e06218b63e695eb72ce74974, 33e974c2d5a82b2f9d9ba0ad9cbaabc1c8e3985f, 67a05679621b7f721bdba37a5d18665d3aceb695; azl3 kernel 6.6.96.2-2 on Azure Linux 3.0 6.6.104.2-1; cbl2 kernel 5.15.186.1-1 on CBL Mariner 2.0 5.15.200.1-1 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

In the Linux kernel, the following vulnerability has been resolved: KVM: x86: use array_index_nospec with indices that come from guest min and dest_id are guest-controlled indices. Using array_index_nospec() after the bounds checks clamps these values to mitigate speculative execution side-channels.

HighCVSS 7.8 · v3.1—No exploit Fix available
Published
Sep 16, 2025
Updated
Nov 5, 2026
EPSS
0.1% · 7th percentile

Report tools

JSON

Action score

31

Monitor

Low priority for now.

CVSS
31 / 40 · 7.8 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.1%

CISA SSVC decision

Exploitation
none
Automatable
no
Technical impact
partial

Vulnrichment: CISA's decision-tree inputs.

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • A fix has been released

If any of these changes, we'll tell you in the daily email digest.

Follow CVE-2025-39823

When you'll hear from us

  • when it enters CISA KEV
  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
linuxlinux kernel
debiandebian linux

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • debian debian linux11.0
  • linux linux kernel5.5 and later · before 5.10.242
  • linux linux kernel5.11 and later · before 5.15.191
  • linux linux kernel5.16 and later · before 6.1.150
  • linux linux kernel4.19 and later · before 5.4.298
  • linux linux kernel6.7 and later · before 6.12.45
  • linux linux kernel6.13 and later · before 6.16.5
  • linux linux kernel6.2 and later · before 6.6.104
  • linux linux kernel6.17

Versions reported by the vendor

Affected version ranges reported by the assigning authority (Linux). Independent of NVD's CPE analysis and usually ahead of it.

  • Linux Linux

    • 4.19affected
    • 4180bf1b655a791a0a6ef93a2ffffc762722c782 and later · before 72777fc31aa7ab2ce00f44bfa3929c6eabbeaf48affected · git
    • 4180bf1b655a791a0a6ef93a2ffffc762722c782 and later · before 31a0ad2f60cb4816e06218b63e695eb72ce74974affected · git
    • 4180bf1b655a791a0a6ef93a2ffffc762722c782 and later · before d51e381beed5e2f50f85f49f6c90e023754efa12affected · git
    • 4180bf1b655a791a0a6ef93a2ffffc762722c782 and later · before 33e974c2d5a82b2f9d9ba0ad9cbaabc1c8e3985faffected · git
    • 4180bf1b655a791a0a6ef93a2ffffc762722c782 and later · before f49161646e03d107ce81a99c6ca5da682fe5fb69affected · git
    • 4180bf1b655a791a0a6ef93a2ffffc762722c782 and later · before 67a05679621b7f721bdba37a5d18665d3aceb695affected · git
    • 4180bf1b655a791a0a6ef93a2ffffc762722c782 and later · before f57a4bd8d6cb5af05b8ac1be9098e249034639fbaffected · git
    • 4180bf1b655a791a0a6ef93a2ffffc762722c782 and later · before c87bd4dd43a624109c3cc42d843138378a7f4548affected · git
    • before 4.19not affected · semver

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Debian:12linuxbefore 6.1.153-16.1.153-1
Debian:13linuxbefore 6.12.48-16.12.48-1
Debian:14linuxbefore 6.16.5-16.16.5-1

Same product

linux: all records

Other highest-scoring records for the same primary product.

  • CVE-2026-31431crypto: algif_aead - Revert to operating out-of-placeKEV
    90Now
  • CVE-2022-0847A flaw was found in the way the "flags" member of the new pipe buffer structure was lacking proper initialization in copy_page_to_iter_pipe KEV
    89Now
  • CVE-2021-22555Heap Out-Of-Bounds Write in Netfilter IP6T_SO_SET_REPLACEKEV
    85Now

Published before and after this one in the same product

  • ← EarlierCVE-2025-39821Sep 16, 2025 · perf: Avoid undefined behavior from stopping/starting inactive events
    31Monitor
  • ← EarlierCVE-2025-39822Sep 16, 2025 · io_uring/kbuf: fix signedness in this_len calculation
    22Monitor
  • Later →CVE-2025-39824Sep 16, 2025 · HID: asus: fix UAF via HID_CLAIMED_INPUT validation
    31Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
Linux Linux31a0ad2f60cb4816e06218b63e695eb72ce74974Vendor (CNA)
Linux Linux33e974c2d5a82b2f9d9ba0ad9cbaabc1c8e3985fVendor (CNA)
Linux Linux67a05679621b7f721bdba37a5d18665d3aceb695Vendor (CNA)
Linux Linux72777fc31aa7ab2ce00f44bfa3929c6eabbeaf48Vendor (CNA)
Linux Linuxc87bd4dd43a624109c3cc42d843138378a7f4548Vendor (CNA)
Linux Linuxd51e381beed5e2f50f85f49f6c90e023754efa12Vendor (CNA)
Linux Linuxf49161646e03d107ce81a99c6ca5da682fe5fb69Vendor (CNA)
Linux Linuxf57a4bd8d6cb5af05b8ac1be9098e249034639fbVendor (CNA)
azl3 kernel 6.6.96.2-2 on Azure Linux 3.06.6.104.2-1 · CBL-Mariner ReleasesMicrosoft (MSRC)
cbl2 kernel 5.15.186.1-1 on CBL Mariner 2.05.15.200.1-1 · CBL-Mariner ReleasesMicrosoft (MSRC)
debian:linux6.1.153-1 · Debian:12Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

  • CVE-2021-47548480 days apartethernet: hisilicon: hns: hns_dsaf_misc: fix a possible array overflow in hns_dsaf_ge_srst_by_port()
    39Monitor
  • CVE-2026-64018306 days apartnet: mana: validate rx_req_idx to prevent out-of-bounds array access
    37Monitor
  • CVE-2026-23246183 days apartwifi: mac80211: bounds-check link_id in ieee80211_ml_reconfiguration
    35Monitor
  • CVE-2026-43110232 days apartwifi: brcmfmac: validate bsscfg indices in IF events
    35Monitor
  • CVE-2026-43172232 days apartwifi: iwlwifi: fix 22000 series SMEM parsing
    35Monitor
  • CVE-2022-503151 days apartata: ahci: Match EM_MAX_SLOTS with SATA_PMP_MAX_PORTS
    31Monitor

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

  • Someone with local access to the system can trigger it.
  • A low-privileged account is enough.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
high · data can be read
Integrity
high · data or configuration can be modified
Availability
high · the service can be disrupted
Attack vector
Local
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality impact
High
Integrity impact
High
Availability impact
High

Weakness class (CWE)

CWE-129 · Improper Validation of Array Index

CVSS vector

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

nvd-primary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

ATT&CK techniques

—

Change log

  1. SSVC exploitation— → none
  2. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Show all references (10 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records