CVE-2026-69637: Windows 10 1607 DHCP Server DOS Vulnerability

CVE-2026-69637 Overview

CVE-2026-69637 is an out-of-bounds read vulnerability [CWE-125] in the Microsoft Windows Dynamic Host Configuration Protocol (DHCP) Server service. An authorized attacker on an adjacent network can trigger the flaw to cause a denial-of-service condition against the DHCP Server. The issue affects multiple supported Windows Server releases and legacy Windows 10 builds that ship the DHCP Server component. Microsoft published the advisory on September 8, 2026 and rates the issue as medium severity, with availability impact only.

Critical Impact
Successful exploitation disrupts DHCP address leasing on the affected server, which can prevent clients from obtaining or renewing IP configuration across the local network segment.

Affected Products

Microsoft Windows Server 2012, 2012 R2, 2016, 2019, 2022, and 2025
Microsoft Windows 10 version 1607 (x86, x64)
Microsoft Windows 10 version 1809 (x86, x64)

Discovery Timeline

2026-09-08 - CVE-2026-69637 published to NVD
2026-09-09 - Last updated in NVD database

Technical Details for CVE-2026-69637

Vulnerability Analysis

The flaw resides in the Windows DHCP Server service, which manages IP address leases for network clients. An out-of-bounds read occurs when the service processes a specially crafted DHCP message and accesses memory outside the intended buffer bounds. Reading past the buffer causes an unhandled condition that terminates the DHCP Server process. The attacker requires low-privileged credentials on an adjacent network and no user interaction to trigger the condition. Confidentiality and integrity are not impacted, but the DHCP service becomes unavailable to legitimate clients on the segment.

Root Cause

The vulnerability is classified as an out-of-bounds read [CWE-125]. The DHCP Server parses attacker-supplied protocol fields without sufficient bounds checking, permitting the service to read memory beyond the allocated buffer. Microsoft's advisory does not publicly disclose the specific handler or field involved. See the Microsoft CVE-2026-69637 Advisory for vendor details.

Attack Vector

Exploitation requires network adjacency, meaning the attacker must reside on the same broadcast domain or logically adjacent network as the DHCP Server. The attacker must also hold at least low-level privileges on the network. From that position, the attacker sends a malformed DHCP request or related protocol message to the server. The service reads out-of-bounds memory during parsing and crashes, denying DHCP services to all clients relying on the affected server. No proof-of-concept exploit is publicly available at the time of publication, and the vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog.

Detection Methods for CVE-2026-69637

Indicators of Compromise

Unexpected termination or repeated restarts of the DHCPServer service on affected Windows Server hosts.
Windows Event Log entries in the System and DhcpAdminEvents channels showing service crashes, faulting module references, or lease processing failures.
Sudden inability of clients on a subnet to acquire or renew DHCP leases coinciding with malformed inbound DHCP traffic.

Detection Strategies

Monitor DHCP Server process stability and correlate crash events with inbound DHCP traffic captured on UDP ports 67 and 68.
Inspect DHCP packet captures for malformed option fields, oversized payloads, or protocol violations originating from authenticated network hosts.
Alert on repeated service restarts of DHCPServer.exe within short time windows, which may indicate exploitation attempts.

Monitoring Recommendations

Forward Windows DHCP Server audit and operational logs to a centralized SIEM for correlation with network telemetry.
Baseline normal DHCP request patterns per subnet and alert on statistical anomalies in message volume or option composition.
Track authenticated user activity on segments that host DHCP infrastructure to identify low-privilege accounts probing the service.

How to Mitigate CVE-2026-69637

Immediate Actions Required

Apply the Microsoft security update referenced in the Microsoft CVE-2026-69637 Advisory to all affected Windows Server and Windows 10 systems running the DHCP Server role.
Inventory DHCP Server deployments across the environment and prioritize patching of servers exposed to untrusted or user-accessible network segments.
Restrict access to the DHCP Server management network using segmentation and access control lists.

Patch Information

Microsoft has issued security updates for all affected products. Refer to the Microsoft CVE-2026-69637 Advisory for the specific KB articles and update packages that correspond to each supported Windows release. Install the updates through Windows Update, Windows Server Update Services (WSUS), or your patch management platform.

Workarounds

Where patching cannot be performed immediately, isolate DHCP Servers on dedicated management VLANs and restrict which hosts can send DHCP traffic to them.
Enforce DHCP snooping and port security on network switches to limit rogue or unauthorized DHCP client traffic reaching the server.
Configure DHCP failover or a secondary DHCP Server on the segment so lease services continue if the primary service crashes.

bash

# Verify the DHCP Server service state and review recent crash events on Windows Server
Get-Service -Name DHCPServer
Get-WinEvent -LogName System -MaxEvents 200 | Where-Object { $_.ProviderName -like '*Dhcp*' -or $_.Message -like '*DHCPServer*' }