CVE-2026-69845: Windows 10 1607 Buffer Overflow Vulnerability

CVE-2026-69845 Overview

CVE-2026-69845 is a heap-based buffer overflow in the Microsoft Windows Dynamic Host Configuration Protocol (DHCP) Server service. An unauthenticated remote attacker can exploit this flaw by sending crafted DHCP traffic to a vulnerable server, resulting in arbitrary code execution in the context of the DHCP service. The weakness is rooted in improper input validation [CWE-20] during message processing on the server. Because DHCP servers commonly run with high privileges on Windows domain infrastructure, successful exploitation gives attackers a foothold suitable for lateral movement and privilege escalation across the network.

Critical Impact
Unauthenticated network-based remote code execution against Windows DHCP Server, affecting Windows Server 2012 through Windows Server 2025.

Affected Products

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

Discovery Timeline

2026-09-08 - CVE-2026-69845 published to the National Vulnerability Database
2026-09-10 - Last updated in NVD database

Technical Details for CVE-2026-69845

Vulnerability Analysis

The vulnerability resides in the Windows DHCP Server service, which listens on UDP port 67 for client requests. The service fails to correctly validate the size or structure of attacker-supplied fields within a DHCP message before copying data into a heap-allocated buffer. This condition allows an out-of-bounds write on the heap, corrupting adjacent memory structures.

Because DHCP servers accept broadcast and unicast messages from unauthenticated clients on the local network segment, exploitation does not require credentials or user interaction. An attacker with network reachability to the DHCP service can trigger the flaw remotely. Successful memory corruption enables control-flow hijacking and arbitrary code execution in the DHCP service process.

Windows DHCP Server typically runs as NT AUTHORITY\SYSTEM or an equivalently privileged service account. Code execution in this context provides full local control of the host and a pivot point into Active Directory and adjacent network segments.

Root Cause

The root cause is improper input validation [CWE-20] leading to a heap-based buffer overflow. The DHCP Server component does not enforce bounds checks on attacker-controlled length or option fields before writing them into a fixed-size heap buffer, allowing adjacent heap metadata and object pointers to be overwritten.

Attack Vector

Exploitation occurs entirely over the network. An attacker sends a specially crafted DHCP message, such as a DHCPDISCOVER or DHCPREQUEST, containing malformed options or oversized fields to the DHCP Server. No authentication is required, and the attack requires no user interaction. Public technical details and proof-of-concept code are not currently available. Consult the Microsoft Security Update for CVE-2026-69845 for authoritative details.

Detection Methods for CVE-2026-69845

Indicators of Compromise

Unexpected crashes, restarts, or Windows Error Reporting entries for the DHCPServer service (svchost.exe hosting dhcpssvc.dll).
Anomalous child processes spawned by the DHCP Server service host, particularly command shells or scripting interpreters.
Outbound network connections initiated from a DHCP server host to unknown external endpoints shortly after receipt of DHCP traffic.

Detection Strategies

Enable DHCP audit logging and inspect logs under %windir%\System32\dhcp\ for malformed packets, parsing errors, or high volumes of requests from a single source.
Deploy endpoint behavioral analytics on DHCP servers to identify service crashes followed by process creation or memory injection activity.
Correlate Windows Event Log entries for service failures (Event IDs 7031, 7034) with network telemetry showing DHCP option anomalies.

Monitoring Recommendations

Monitor UDP port 67 for oversized packets or non-standard option fields using network intrusion detection signatures.
Alert on any process creation whose parent is the DHCP Server service host on servers running the DHCP role.
Track privileged account activity originating from DHCP servers for signs of lateral movement into Active Directory.

How to Mitigate CVE-2026-69845

Immediate Actions Required

Apply the Microsoft security update for CVE-2026-69845 to all Windows Server systems running the DHCP Server role.
Inventory all hosts with the DHCP Server role enabled, including Windows 10 1607 and 1809 systems, and prioritize patching for internet- or perimeter-exposed servers.
Restrict network reachability of the DHCP service to trusted client subnets using firewall rules and VLAN segmentation.

Patch Information

Microsoft has released a security update addressing this vulnerability. Refer to the Microsoft Security Update Guide for CVE-2026-69845 for the specific KB articles and update packages that apply to each affected Windows version.

Workarounds

If patching cannot be completed immediately, disable the DHCP Server service on hosts where it is not required and migrate DHCP functionality to a patched server.
Block unsolicited UDP traffic to port 67 on hosts that do not require the DHCP Server role using the Windows Firewall or upstream network ACLs.
Enforce DHCP snooping and rate limiting on network switches to reduce exposure to malformed DHCP messages from untrusted ports.

bash

# Disable the DHCP Server service on hosts where the role is not required
sc.exe stop DHCPServer
sc.exe config DHCPServer start= disabled

# Block inbound DHCP server traffic at the Windows Firewall
netsh advfirewall firewall add rule name="Block DHCP Server Inbound" ^
  dir=in action=block protocol=UDP localport=67