MSRC-CVE-2026-56159 — DHCP Server Service Remote Code Execution Vulnerability

Summary

Impact: Remote Code Execution. Microsoft rating: Critical. Not known to be exploited — Exploitation Unlikely. Customer action: Required.

Details

How could an attacker exploit this vulnerability?
An unauthenticated attacker could exploit this vulnerability by sending specially crafted packet to a Dynamic Host Configuration Protocol (DHCP) Server configured to provide data for Option 43.

Security updates
10.0.17763.9020 — https://support.microsoft.com/help/5099538
10.0.20348.5386 — https://support.microsoft.com/help/5099540
10.0.26100.33158 — https://support.microsoft.com/help/5099536
10.0.14393.9339 — https://support.microsoft.com/help/5099535
6.2.9200.26226 — https://support.microsoft.com/help/5099445
6.3.9600.23291 — https://support.microsoft.com/help/5099444

Vulnerabilities 1

Critical 9.8

CVE-2026-56159

DHCP Server Service Remote Code Execution Vulnerability

Heap-based buffer overflow in Windows DHCP Server allows an unauthorized attacker to execute code over a network.

Microsoft Windows Server 2019 Windows Server 2019 (Server Core installation) Windows 10 Version 1809 Windows

Jul 14, 2026

Revision history

2026-07-27 #3
Updated an acknowledgement. This is an informational change only.
2026-07-17 #2
Added acknowledgements. This is an informational change only.
2026-07-14 #1
Information published.

References

CVE-2026-56159 DHCP Server Service Remote Code Execution Vulnerability - HTML
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-56159
Microsoft Exploitability Index
https://www.microsoft.com/en-us/msrc/exploitability-index?rtc=1
Microsoft Support Lifecycle
https://support.microsoft.com/lifecycle
Common Vulnerability Scoring System
https://www.first.org/cvss