Microsoft Security Response CenterCVE-2026-77499

Windows DHCP Server Denial of Service Vulnerability

Access of resource using incompatible type ('type confusion') in Windows DHCP Server allows an unauthorized attacker to deny service over a network.

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7.5CVSS out of 10High severity

Scope

What the vendor says is affected

Windows 10 Version 1809 for 32-bit Systems
Windows 10 Version 1809 for x64-based Systems
Windows Server 2019
Windows Server 2019 (Server Core installation)
Windows Server 2022
Windows Server 2022 (Server Core installation)
Windows Server 2025 (Server Core installation)
Windows Server 2025
Windows 10 Version 1607 for 32-bit Systems
Windows 10 Version 1607 for x64-based Systems
Windows Server 2016
Windows Server 2016 (Server Core installation)
Windows Server 2012
Windows Server 2012 (Server Core installation)
Windows Server 2012 R2
Windows Server 2012 R2 (Server Core installation)

Versions the vendor lists as fixed

10.0.17763.9245
10.0.20348.5622
10.0.26100.33438
10.0.14393.9512
6.2.9200.26349
6.3.9600.23397

Next step

What the vendor recommends

Install KB5122876. Install KB5122882. Install KB5122871. Install KB5123099. Install KB5123065. Install KB5123066.

Review the complete instructions on the vendor's site

Update history

What changed in later vendor updates

SecurityAlert records field-level changes from the point we begin following a bulletin. Earlier vendor changes may not have a field-by-field record.

Sep 11, 2026 at 8:15 PM UTC
- The vendor changed the advisory's last-updated date.

Timeline

When this advisory changed

Sep 8, 2026 at 7:00 AM UTC
Published by Microsoft Security Response Center
The publication date reported by the vendor.
Sep 8, 2026 at 7:15 PM UTC
Added to SecurityAlert
We collected the advisory from the official source.
Sep 11, 2026 at 7:00 AM UTC
Updated by Microsoft Security Response Center
The vendor changed the advisory after it was first published.
Sep 13, 2026 at 2:40 AM UTC
Confirmed at the source
Our collector saw this advisory during a later source check.

Vulnerabilities

CVEs named in this advisory

CVE-2026-77499View CVSS, KEV, EPSS, and threat context

Source

Start with the vendor's bulletin

SecurityAlert organizes the fields the vendor published. The original bulletin remains the source of record for affected versions, fixes, and later changes.

Vendor: Microsoft Security Response Center
Advisory ID: CVE-2026-77499
Last source check: Sep 13, 2026 at 2:40 AM UTC

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What the vendor says is affected

Versions the vendor lists as fixed

What the vendor recommends

What changed in later vendor updates

When this advisory changed

CVEs named in this advisory

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