Microsoft Windows Server AD CS: Security feature bypass through improper certificate validation
Summary
Improper certificate validation in Active Directory Certificate Services (AD CS) on Windows Server allows an authorized attacker to bypass a security feature over the network. Successful exploitation affects integrity only; confidentiality and availability are not impacted. Exploitation requires low privileges and high attack complexity, and Microsoft does not know of any exploitation.
Affected
- Windows Server 2016 and Server Core installation: 10.0.14393.0 before 10.0.14393.9688
- Windows Server 2019 and Server Core installation: 10.0.17763.0 before 10.0.17763.9487
- Windows Server 2022: 10.0.20348.0 before 10.0.20348.5870
- Windows Server 2025 and Server Core installation: 10.0.26100.0 before 10.0.26100.33822
- Only systems with the AD CS role are relevant.
Fixed in
- Security updates from the November 2026 Patch Tuesday for the affected Windows Server versions.
- Third-party trackers name KB5131080 (Server 2025) and KB5131085 (Server 2019); not verified against the Microsoft Update Catalog.
- Server 2016, Server 2022 and Server Core: KB number unknown; check MSRC.
Workaround
Unknown beyond patching. The retrieved MSRC text lists no specific workaround; check the MSRC Workarounds section directly.
Exploitation
- Microsoft: not publicly disclosed, not exploited, exploitability assessment "Exploitation Less Likely".
- No public exploit code known as of 11 November 2026.
- Not listed in CISA KEV.
Our recommendation
- Check whether AD CS is installed (Get-WindowsFeature ADCS-Cert-Authority).
- Where AD CS runs, install the November 2026 security updates as a priority; treat the Certificate Authority as a Tier 0 asset.
- Verify the KB number and the affected build for your Windows Server version in the MSRC table before deployment.
- Review certificate templates and lock down web enrollment; confirm Extended Protection for Authentication and HTTPS settings.
- Systems without the AD CS role are not affected.
Information from Microsoft (Patch Tuesday November 2026)
- Severity (Microsoft)
- Important
- Impact
- Security feature bypass – Windows Active Directory Certificate Services
- Status on Patch Tuesday
- Neither exploited nor publicly disclosed
- Exploitability assessment
- Exploitation less likely
- Product family
- Windows, Windows ESU (Extended Security Updates)
- Updates (KB)
- KB5131291, KB5131085, KB5131090, KB5131080, KB5131077
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- Microsoft Security Update Guide: CVE-2026-105590 msrc.microsoft.com
- CVE.org record CVE-2026-105590 www.cve.org
- OpenCVE: CVE-2026-105590 app.opencve.io
- Senserva KB5131080 (Server 2025) senserva.com
- Senserva KB5131085 (Server 2019) senserva.com
- Rapid7: November 2026 Patch Tuesday www.rapid7.com
- Encryption Consulting: AD CS attacks 2026 www.encryptionconsulting.com
- Cybersecurity News: November 2026 Patch Tuesday cybersecuritynews.com
Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 11 Nov 2026, 18:36.
Original description (NVD)
Improper certificate validation in Windows Active Directory Certificate Services allows an authorized attacker to bypass a security feature over a network.
NVD references (1)
Sources
The tracker combines official, freely usable data sources – updated continuously:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.
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