CVE-2026-50518: Windows DHCP Server Buffer Overflow Flaw

CVE-2026-50518 Overview

CVE-2026-50518 is a heap-based buffer overflow vulnerability in Windows Dynamic Host Configuration Protocol (DHCP) Server. The flaw allows an unauthenticated attacker to execute arbitrary code over the network by sending crafted DHCP traffic to a vulnerable server. Because DHCP servers routinely process untrusted client packets, exploitation requires no user interaction and no prior privileges. The vulnerability is tracked under CWE-122: Heap-based Buffer Overflow and is documented in the Microsoft CVE-2026-50518 Advisory.

Critical Impact
Unauthenticated remote code execution against Windows DHCP Server infrastructure, enabling attacker control of a core network service.

Affected Products

Windows DHCP Server (per Microsoft advisory)
Refer to the Microsoft Security Response Center advisory for the authoritative list of affected Windows Server builds
Environments running DHCP Server role reachable from untrusted network segments

Discovery Timeline

2026-07-14 - CVE-2026-50518 published to NVD
2026-07-15 - Last updated in NVD database

Technical Details for CVE-2026-50518

Vulnerability Analysis

The vulnerability resides in the Windows DHCP Server service, which parses inbound DHCP client messages such as DISCOVER, REQUEST, and INFORM. A heap-based buffer overflow occurs during processing of attacker-controlled fields in these messages. An unauthorized attacker on the network can trigger the overflow without authentication or user interaction.

Successful exploitation corrupts adjacent heap structures within the DHCP service process, which typically runs with elevated privileges on Windows Server. Attackers can leverage this corruption to hijack execution flow and run arbitrary code in the security context of the DHCP service. The EPSS score of 7.356% places this vulnerability in the 93rd percentile for expected exploitation activity.

Root Cause

The root cause is improper validation of the length or structure of one or more fields within a DHCP message before copying data into a heap-allocated buffer. When the supplied data exceeds the allocated buffer size, adjacent heap memory is overwritten. This class of defect (CWE-122) commonly leads to control-flow hijacking through corruption of function pointers, virtual table pointers, or heap metadata.

Attack Vector

Exploitation requires only network reachability to UDP port 67 on the target DHCP server. An attacker sends one or more crafted DHCP packets that carry oversized or malformed option fields. Because DHCP is broadcast-oriented and often traverses trusted internal networks, an attacker with any foothold in the broadcast domain — or in some deployments across relayed segments — can reach the vulnerable service. No credentials, user interaction, or prior access to the host are required.

Microsoft has not released public exploitation details. See the Microsoft advisory for vendor guidance.

Detection Methods for CVE-2026-50518

Indicators of Compromise

Unexpected crashes, restarts, or access violations of the DHCPServer service (svchost.exe hosting dhcpssvc.dll)
Anomalous child processes spawned by the DHCP Server service, such as cmd.exe, powershell.exe, or rundll32.exe
Malformed DHCP packets with oversized option fields captured on UDP port 67
Outbound connections from a DHCP server host to unfamiliar external IP addresses shortly after receiving DHCP traffic

Detection Strategies

Monitor Windows Event Log for DHCP Server service faults and Windows Error Reporting entries referencing dhcpssvc.dll
Deploy network intrusion detection signatures that flag DHCP options exceeding RFC-defined length constraints
Correlate DHCP service crashes with subsequent process creation events on the same host using EDR telemetry

Monitoring Recommendations

Baseline normal DHCP traffic volume and option composition, then alert on deviations
Track process lineage for the DHCP service and alert on any non-standard child process
Forward Windows Server security, system, and Sysmon logs from DHCP servers to a centralized analytics platform for retention and correlation

How to Mitigate CVE-2026-50518

Immediate Actions Required

Apply the Microsoft security update referenced in the MSRC advisory for CVE-2026-50518 to all Windows Servers running the DHCP Server role
Inventory all hosts with the DHCP Server role enabled and prioritize patching those exposed to less trusted network segments
Restrict inbound UDP 67 traffic to DHCP servers using firewall rules and VLAN segmentation where feasible
Enable enhanced logging on DHCP servers to capture pre- and post-patch activity for forensic review

Patch Information

Microsoft has issued a security update addressing the heap-based buffer overflow in the Windows DHCP Server service. Consult the Microsoft CVE-2026-50518 Advisory for the specific KB article, build numbers, and installation guidance applicable to each affected Windows Server version.

Workarounds

If immediate patching is not possible, restrict access to UDP port 67 on affected DHCP servers to trusted network segments only
Consider temporarily relocating DHCP services to a patched host or using DHCP relay agents to reduce direct exposure
Disable the DHCP Server role on hosts where it is not required
Monitor DHCP service telemetry closely until the security update is deployed

bash

# Example: restrict inbound DHCP traffic on a Windows DHCP server using PowerShell
New-NetFirewallRule -DisplayName "Restrict DHCP Server Inbound" `
  -Direction Inbound `
  -Protocol UDP `
  -LocalPort 67 `
  -RemoteAddress 10.0.0.0/8 `
  -Action Allow

# Block all other inbound UDP 67 traffic
New-NetFirewallRule -DisplayName "Block Untrusted DHCP Inbound" `
  -Direction Inbound `
  -Protocol UDP `
  -LocalPort 67 `
  -RemoteAddress Any `
  -Action Block