CVE-2026-20856
HIGHCVSS 8.1/10EPSS 1.07%
Last modified
CVE-2026-20856 is a high-severity vulnerability rated 8.1/10 on the CVSS scale. Improper input validation in Windows Server Update Service allows an unauthorized attacker to execute code over a network.. EPSS estimates a 1.07% chance of exploitation in the next 30 days.
Description
Improper input validation in Windows Server Update Service allows an unauthorized attacker to execute code over a network.
Metrics
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
Weakness Enumeration
Affected Software
| Vendor | Product | Versions |
|---|---|---|
| Microsoft | Windows 10 1607 | < 10.0.14393.8783 |
| Microsoft | Windows 10 1809 | < 10.0.17763.8276 |
| Microsoft | Windows 10 21h2 | < 10.0.19044.6809 |
| Microsoft | Windows 10 22h2 | < 10.0.19045.6809 |
| Microsoft | Windows 11 23h2 | < 10.0.22631.6491 |
| Microsoft | Windows 11 24h2 | < 10.0.26100.7623 |
| Microsoft | Windows 11 25h2 | < 10.0.26200.7623 |
| Microsoft | Windows Server 2012 | All versions |
| Microsoft | Windows Server 2012 | r2 |
| Microsoft | Windows Server 2016 | < 10.0.14393.8783 |
| Microsoft | Windows Server 2019 | < 10.0.17763.8276 |
| Microsoft | Windows Server 2022 | < 10.0.20348.4648 |
| Microsoft | Windows Server 2022 23h2 | < 10.0.25398.2092 |
| Microsoft | Windows Server 2025 | < 10.0.26100.32230 |
References
Timeline
- Published
- Last Modified
- Status
- Analyzed
Frequently Asked Questions
What is CVE-2026-20856?
Improper input validation in Windows Server Update Service allows an unauthorized attacker to execute code over a network.
How severe is CVE-2026-20856?
CVE-2026-20856 has a CVSS score of 8.1/10 (HIGH severity). The EPSS model estimates a 1.07% probability of exploitation in the next 30 days.
How do I fix CVE-2026-20856?
Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.
How Strix Helps
- How Strix found a critical auth bypass in etcdStrix autonomously discovered a critical authentication bypass in etcd, later designated CVE-2026-33413.
- Autonomous PentestingAI agents that find and validate exploitable vulnerabilities like this one across your applications.
- PR ReviewsPentest every pull request so vulnerable code is caught before it ships to production.
- AI Penetration TestingHow AI-driven penetration testing continuously covers your attack surface.
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Are you affected by CVE-2026-20856?
Run a free Strix scan to check your systems for this vulnerability.
Scan your code nowSource: NVD / NIST