CVE-2026-69679: Windows 10 1607 DHCP Server DOS Vulnerability

CVE-2026-69679 Overview

CVE-2026-69679 is an out-of-bounds read vulnerability [CWE-125] in the Microsoft Windows Dynamic Host Configuration Protocol (DHCP) Server service. An authenticated attacker on an adjacent network can trigger the flaw to cause a denial-of-service condition on the DHCP server. The vulnerability affects a wide range of supported Windows client and server versions, including Windows Server 2012 through Windows Server 2025. Microsoft published the advisory on September 8, 2026 and assigned it a medium severity rating. No public exploit code, proof-of-concept, or in-the-wild exploitation has been reported at the time of publication.

Critical Impact
Successful exploitation disrupts DHCP address leasing, which can prevent clients from acquiring or renewing IP addresses across affected network segments.

Affected Products

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

Discovery Timeline

2026-09-08 - CVE-2026-69679 published to NVD
2026-09-09 - Last updated in NVD database

Technical Details for CVE-2026-69679

Vulnerability Analysis

The flaw resides in the Windows DHCP Server service, which allocates IP addresses and network configuration data to clients on a local network. An out-of-bounds read occurs when the service processes a malformed DHCP message and reads memory outside the intended buffer boundary. The invalid memory access causes the DHCP service process to terminate or become unresponsive. Clients on the affected network then fail to acquire new leases or renew existing ones. The impact is limited to availability; the vulnerability does not expose confidentiality or integrity of data, per the Microsoft advisory.

Root Cause

The root cause is missing or insufficient bounds validation when the DHCP server parses attacker-controlled fields in an incoming DHCP packet. The condition is classified under CWE-125: Out-of-bounds Read. Detailed root-cause information beyond the Microsoft advisory has not been published.

Attack Vector

Exploitation requires the attacker to be on an adjacent network segment, such as the same broadcast domain as the DHCP server, and to hold low-privilege authenticated access. The attacker sends a specially crafted DHCP request or related protocol message to the vulnerable server. User interaction is not required. Because DHCP relies on broadcast and relay traffic, an attacker with a foothold on a trusted VLAN or via a compromised host can reach the service. See the Microsoft CVE-2026-69679 Update Guide for vendor-provided technical context.

Detection Methods for CVE-2026-69679

Indicators of Compromise

Unexpected termination or repeated restarts of the DHCPServer service (dhcpserver.exe) on affected hosts.
Windows Event Log entries indicating a DHCP service crash or Service Control Manager restart events for the DHCP role.
Spikes in DHCPDISCOVER or DHCPREQUEST traffic from a single adjacent source preceding a service outage.

Detection Strategies

Monitor Windows System and Application event logs for DHCP service faults and application error events referencing dhcpserver.exe.
Baseline DHCP traffic patterns and alert on abnormal packet rates or malformed option fields observed by network sensors.
Correlate authenticated network sessions on adjacent VLANs with DHCP availability incidents to identify potential source hosts.

Monitoring Recommendations

Enable DHCP audit logging and forward logs to a centralized SIEM for correlation with endpoint telemetry.
Alert on client-side DHCP renewal failures across multiple hosts within short time windows.
Track service uptime and process crash telemetry for the DHCP server role.

How to Mitigate CVE-2026-69679

Immediate Actions Required

Apply the Microsoft security update referenced in the Microsoft CVE-2026-69679 Update Guide to all affected Windows Server and Windows 10 systems running the DHCP Server role.
Inventory hosts running the DHCP Server service and prioritize patching for servers on segments accessible to less trusted clients.
Restrict which authenticated users and devices can reach DHCP server segments while updates are staged.

Patch Information

Microsoft has released updates addressing CVE-2026-69679 for Windows Server 2012, 2012 R2, 2016, 2019, 2022, 2025, and Windows 10 versions 1607 and 1809. Refer to the vendor advisory for the specific KB numbers applicable to each affected build and installation channel.

Workarounds

Segment the network so that DHCP servers only accept traffic from trusted VLANs and authorized relay agents.
Enforce DHCP snooping and port security on access switches to limit rogue or malformed DHCP traffic from adjacent hosts.
Deploy redundant DHCP servers with failover configured to maintain lease availability if a primary service is disrupted.

bash

# Example: verify DHCP service status and recent crashes on Windows Server
Get-Service -Name DHCPServer
Get-WinEvent -LogName System -MaxEvents 200 | Where-Object { $_.ProviderName -like '*DHCP*' -or $_.Message -like '*dhcpserver*' }