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Microsoft Security Response CenterCVE-2026-23666

.NET Framework Denial of Service Vulnerability

Improper input validation in .NET Framework allows an unauthorized attacker to deny service over a network.

Read the vendor bulletin Get alerts for Microsoft .NET Framework 4.8 on Windows
7.5CVSS out of 10Critical severity
Scope

What the vendor says is affected

  • Microsoft .NET Framework 4.8 on Windows 10 Version 1607 for 32-bit Systems
  • Microsoft .NET Framework 4.8 on Windows 10 Version 1607 for x64-based Systems
  • Microsoft .NET Framework 4.8 on Windows Server 2012
  • Microsoft .NET Framework 4.8 on Windows Server 2012 (Server Core installation)
  • Microsoft .NET Framework 4.8 on Windows Server 2012 R2
  • Microsoft .NET Framework 4.8 on Windows Server 2012 R2 (Server Core installation)
  • Microsoft .NET Framework 3.5 AND 4.8 on Windows 10 Version 1809 for 32-bit Systems
  • Microsoft .NET Framework 3.5 AND 4.8 on Windows 10 Version 1809 for x64-based Systems
  • Microsoft .NET Framework 3.5 AND 4.8 on Windows 10 Version 1809 for ARM64-based Systems
  • Microsoft .NET Framework 3.5 AND 4.8 on Windows Server 2022
  • Microsoft .NET Framework 3.5 AND 4.8 on Windows Server 2022 (Server Core installation)
  • Microsoft .NET Framework 3.5 AND 4.8 on Windows 10 Version 21H2 for 32-bit Systems
  • Microsoft .NET Framework 3.5 AND 4.8 on Windows 10 Version 21H2 for ARM64-based Systems
  • Microsoft .NET Framework 3.5 AND 4.8 on Windows 10 Version 21H2 for x64-based Systems
  • Microsoft .NET Framework 3.5 AND 4.8 on Windows 10 Version 22H2 for x64-based Systems
  • Microsoft .NET Framework 3.5 AND 4.8 on Windows 10 Version 22H2 for ARM64-based Systems
  • Microsoft .NET Framework 3.5 AND 4.8 on Windows 10 Version 22H2 for 32-bit Systems
  • Microsoft .NET Framework 3.5 AND 4.7.2 on Windows 10 Version 1809 for 32-bit Systems
  • Microsoft .NET Framework 3.5 AND 4.7.2 on Windows 10 Version 1809 for x64-based Systems
  • Microsoft .NET Framework 3.5 AND 4.7.2 on Windows 10 Version 1809 for ARM64-based Systems
  • Microsoft .NET Framework 4.6.2/4.7/4.7.1/4.7.2 on Windows Server 2012
  • Microsoft .NET Framework 4.6.2/4.7/4.7.1/4.7.2 on Windows Server 2012 (Server Core installation)
  • Microsoft .NET Framework 4.6.2/4.7/4.7.1/4.7.2 on Windows Server 2012 R2
  • Microsoft .NET Framework 4.6.2/4.7/4.7.1/4.7.2 on Windows Server 2012 R2 (Server Core installation)

Versions the vendor lists as fixed

  • 4.8.4801.0
  • 2.0.50727.9068 & 3.0.30729.9065 & 4.8.4801.0
  • 2.0.50727.9181 & 3.0.30729.9165 & 4.8.4801.0
  • 2.0.50727.9068 & 3.0.30729.9065 & 4.7.4141.0
  • 4.7.4141.0
  • 2.0.50727.9181 & 3.0.30729.9165 & 4.8.9332.0
  • 2.0.50727.8982 & 3.0.30729.8976
Next step

What the vendor recommends

Install KB5082411. Install KB5082403. Install KB5082404. Install KB5082414. Install KB5082427. Install KB5082426. Install KB5082413. Install KB5082400. Install KB5082402. Install KB5082425. Install KB5082419. Install KB5082424. Install KB5082417. Install KB5082418. Install KB5082420. Install KB5082398. Install KB5082406. Install KB5082421.

Review the complete instructions on the vendor's site
Timeline

When this advisory changed

  1. Published by Microsoft Security Response Center

    The publication date reported by the vendor.

  2. Updated by Microsoft Security Response Center

    The vendor changed the advisory after it was first published.

  3. Added to SecurityAlert

    We collected the advisory from the official source.

Vulnerabilities

CVEs named in this advisory

CVE-2026-23666View CVSS, KEV, EPSS, and threat context
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