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Windows Server 2008Operating system · Microsoft

CVE-2025-26647

HIGH · 8.8 CVSS v3.1 Published 2025-04-08
Fix available
A fix is available. Upgrade to 10.0.14393.7969 / 10.0.17763.7136 or later.
See remediation →
94/100
Remediation priority · Urgent
Remotely reachable Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
Improper input validation in Windows Kerberos allows an authorized attacker to elevate privileges over a network.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · moderate confidence

Improper input validation in Windows Kerberos allows an authorized attacker to elevate privileges over a network. The vulnerability stems from insufficient validation of Kerberos protocol messages, enabling authenticated attackers to manipulate authentication flows and gain elevated access.

MitigationApply Microsoft security updates for Windows Kerberos when released. Monitor Microsoft Security Response Center for patch availability and implement network segmentation to limit exposure until remediation.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Windows Server 2008Operating system
Affected:all versions= r2
Windows Server 2012Operating system
Affected:all versions= r2
Windows Server 2016Operating system
Affected:< 10.0.14393.7969
Windows Server 2019Operating system
Affected:< 10.0.17763.7136
Windows Server 2022Operating system
Affected:< 10.0.20348.3453
Windows Server 2022 23h2Operating system
Affected:< 10.0.25398.1551
Windows Server 2025Operating system
Affected:< 10.0.26100.3775

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

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

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify Windows Server version and build
    Open Command Prompt or PowerShell and run 'winver' or 'systeminfo | findstr /B /C:"OS Name" /C:"OS Version"' to obtain the exact Windows Server version and build number
    Affected if The build number is lower than 14393.7969 (Server 2016), 17763.7136 (Server 2019), 20348.3453 (Server 2022), 25398.1551 (Server 2022 23h2), or 26100.3775 (Server 2025); or if running Server 2008/2012 (any version)
  2. Confirm system is a Windows Server
    Check the operating system type by running 'systeminfo' and verifying the OS Name contains 'Server' rather than 'Professional' or 'Enterprise' client editions
    Affected if The system is any edition of Windows Server 2008, 2012, 2016, 2019, 2022, or 2025
  3. Determine if Kerberos authentication is active
    On the target server, run 'klist' to list cached Kerberos tickets; if tickets exist or the system is joined to a domain, Kerberos is in use
    Affected if The system participates in Active Directory domain authentication using Kerberos (default on domain-joined servers)
  4. Identify if system is a Domain Controller
    Run 'netdom query fsmo' or check 'Reg Query HKLM\SYSTEM\CurrentControlSet\Services\NTDS\Parameters' to determine if the server holds the Domain Controller role
    Affected if The server is configured as an Active Directory Domain Controller, as the vulnerability description specifically targets Windows domain controllers

A user is affected if they run any version of Windows Server 2008/2012, or any Windows Server 2016/2019/2022/2022 23h2/2025 with a build number below the specified thresholds, AND the system uses Kerberos authentication (typical on domain controllers and domain-joined servers).

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 10.0.14393.7969 / 10.0.17763.7136 / 10.0.20348.3453 or later
Fixed in 10.0.14393.796910.0.17763.713610.0.20348.3453
Interim mitigation

Apply Microsoft security updates for Windows Kerberos when released. Monitor Microsoft Security Response Center for patch availability and implement network segmentation to limit exposure until remediation.

Recommended fix High confidence

Windows Server 2016 to build 10.0.14393.7969; Windows Server 2019 to build 10.0.17763.7136; Windows Server 2022 to build 10.0.20348.3453; Windows Server 2022 23h2 to build 10.0.25398.1551; Windows Server 2025 to build 10.0.26100.3775. Windows Server 2008 and 2012 are end-of-life with no patch availa

  1. Identify the current Windows Server build version by running 'winver' or 'systeminfo' in command prompt
  2. Download the applicable security update from Microsoft Update Catalog or Windows Update for your specific Windows Server version
  3. For Windows Server 2016: Apply update KB5055529 (build 10.0.14393.7969)
  4. For Windows Server 2019: Apply update KB5055536 (build 10.0.17763.7136)
  5. For Windows Server 2022: Apply update KB5055547 (build 10.0.20348.3453)
  6. For Windows Server 2022 23h2: Apply update KB5055548 (build 10.0.25398.1551)
  7. For Windows Server 2025: Apply update KB5055530 (build 10.0.26100.3775)
  8. Restart the server after applying the update
Caveat Standard patching risks apply (test in staging first); Windows Server 2008/2012 have no patch and require full OS migration

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Windows Server 2008 Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA3.0 h
21.0 hours of engineering $3,680
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Scan for this in your stack

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2025-26647 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data