CVE-2026-44815: Windows DHCP Client Buffer Overflow Flaw

CVE-2026-44815 Overview

CVE-2026-44815 is a stack-based buffer overflow [CWE-121] in the Windows Dynamic Host Configuration Protocol (DHCP) Client. An unauthenticated attacker on an adjacent or routable network can send a malformed DHCP response that overflows a fixed-size stack buffer in the client, leading to remote code execution. Exploitation requires no user interaction and no prior privileges on the target host. The flaw affects the DHCP client service that runs by default on Windows endpoints and servers, making any system that requests an IP lease a potential target. Microsoft has published a security update guide entry tracking the issue.

Critical Impact

Network-reachable code execution against the Windows DHCP Client without authentication or user interaction enables full host compromise via a rogue or spoofed DHCP server response.

Affected Products

• Microsoft Windows (DHCP Client service) — refer to the Microsoft Security Update Guide for CVE-2026-44815 for the authoritative list of affected builds
• Windows client editions running the default DHCP Client service
• Windows Server editions running the default DHCP Client service

Discovery Timeline

• 2026-06-09 - CVE-2026-44815 published to the National Vulnerability Database (NVD)
• 2026-06-09 - Last updated in NVD database

Technical Details for CVE-2026-44815

Vulnerability Analysis

The vulnerability is a stack-based buffer overflow in the Windows DHCP Client. The DHCP Client parses server-supplied messages such as DHCPOFFER and DHCPACK, including variable-length options encoded as type-length-value (TLV) triplets. When the client copies attacker-controlled option data into a fixed-size stack buffer without validating the declared length against the destination size, adjacent stack memory — including saved return addresses and structured exception handler records — can be overwritten. An attacker who controls the contents of a DHCP response can therefore redirect execution flow. Because the DHCP Client service typically runs with elevated privileges, successful exploitation yields code execution in a high-privilege context on the victim host.

Root Cause

The root cause is missing or insufficient bounds checking when the DHCP Client processes option fields from a server response. A length value taken from the network is trusted and used as the copy size into a stack buffer, satisfying the classic [CWE-121] pattern.

Attack Vector

Exploitation occurs over the network. An attacker who can respond to the victim's DHCP discovery — for example, by operating a rogue DHCP server on the same broadcast domain or by injecting forged responses on the path — sends a crafted message containing oversized or malformed options. No authentication, credentials, or user interaction are required. The Windows DHCP Client processes the response automatically as part of normal IP address acquisition or lease renewal.

No verified public proof-of-concept code is available at the time of writing. See the Microsoft Security Update Guide for CVE-2026-44815 for vendor technical details.

Detection Methods for CVE-2026-44815

Indicators of Compromise

• Unexpected DHCP server MAC or IP addresses responding to client DHCPDISCOVER broadcasts on monitored subnets.
• DHCP responses containing options with abnormally large length fields or malformed TLV structures.
• Crashes, restarts, or anomalous child processes spawned by the dhcpcsvc / DHCP Client service (svchost.exe hosting Dhcp).
• New outbound connections from svchost.exe immediately after a DHCP lease event.

Detection Strategies

• Inspect DHCP traffic at the network layer for option fields whose declared length exceeds protocol expectations or the remaining packet size.
• Alert on multiple DHCP servers offering leases on a single VLAN where only one authorized server should exist.
• Correlate Windows DHCP Client service crashes (Event ID 1000/1001 referencing the DHCP client) with concurrent network DHCP activity.
• Hunt for process injection or unexpected memory regions inside the svchost.exe instance hosting the DHCP Client service.

Monitoring Recommendations

• Enable DHCP snooping on managed switches to drop responses from unauthorized servers.
• Forward Windows System and Application event logs and DHCP server logs to a centralized analytics platform for correlation.
• Baseline normal DHCP lease and renewal patterns per subnet to surface deviations.

How to Mitigate CVE-2026-44815

Immediate Actions Required

• Apply the Microsoft security update referenced in the Microsoft Security Update Guide for CVE-2026-44815 to all Windows clients and servers.
• Prioritize patching of systems on untrusted or shared network segments, including guest Wi-Fi, lab networks, and field-deployed endpoints.
• Enable DHCP snooping and port security on access-layer switches to block rogue DHCP servers.
• Restrict layer-2 access so that only authorized devices can place traffic on subnets where Windows hosts request DHCP leases.

Patch Information

Microsoft has released a security update for CVE-2026-44815. Refer to the Microsoft Security Update Guide for CVE-2026-44815 for the list of affected builds and corresponding KB numbers. Deploy the update through Windows Update, Windows Server Update Services (WSUS), or your enterprise patch management system.

Workarounds

• Where feasible, assign static IP addresses to high-value hosts and disable the DHCP Client service to remove the attack surface until patching is complete.
• Segment networks so that untrusted devices cannot reach subnets hosting unpatched Windows systems.
• Configure DHCP snooping trust boundaries so only designated uplink ports may forward DHCP server responses.

# Example: disable the DHCP Client service on a host using static addressing
# Run from an elevated PowerShell prompt
Stop-Service -Name Dhcp -Force
Set-Service  -Name Dhcp -StartupType Disabled

# Example: enable DHCP snooping on a Cisco access switch
# (vendor-neutral pattern; adapt to your platform)
# conf t
#  ip dhcp snooping
#  ip dhcp snooping vlan 10
#  interface GigabitEthernet1/0/24
#   ip dhcp snooping trust