Heap-based Buffer Overflow in Windows DHCP Server

Executive Summary

CVE-2026-56159 is a heap-based buffer overflow vulnerability in the Windows DHCP Server. This flaw allows an unauthorized attacker to execute arbitrary code on a vulnerable system remotely over a network.

A heap-based buffer overflow occurs when a program writes more data to a buffer than it can hold, corrupting memory in the heap. In this case, the vulnerability exists in the Windows DHCP Server, which is responsible for assigning IP addresses and managing network configurations in a local network.

An attacker can exploit this vulnerability without authentication, meaning they do not need valid credentials to trigger the flaw. Successful exploitation could lead to remote code execution, giving the attacker control over the affected system.

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Detection Guidance

Detection of CVE-2026-56159 involves checking for vulnerable versions of the Windows DHCP Server service running on your network. Since this is a heap-based buffer overflow vulnerability, there are no direct commands to detect exploitation attempts, but you can verify the DHCP Server version and patch status.

• Check the installed version of the DHCP Server role on Windows Server systems. Use the following PowerShell command to list DHCP Server versions: Get-WindowsFeature DHCP | Select-Object -Property Name, InstallState, DisplayName.
• Verify if the system has the latest security updates installed. Use the following command to check for installed updates: Get-Hotfix | Where-Object {$_.HotFixID -like 'KB*'} | Select-Object HotFixID, InstalledOn.
• Monitor network traffic for unusual DHCP requests or responses that may indicate exploitation attempts. Tools like Wireshark or Microsoft Network Monitor can be used to capture and analyze DHCP traffic.

Refer to Microsoft's official guidance for specific indicators of compromise or detection methods.

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Impact Analysis

This vulnerability can have severe impacts if exploited, including:

• Remote Code Execution: An attacker can execute arbitrary code on the vulnerable Windows DHCP Server, potentially taking full control of the system.
• Network Compromise: Since DHCP servers manage IP address assignments, an attacker could disrupt network operations or use the compromised server as a pivot point to attack other systems on the network.
• Data Theft or Manipulation: If the attacker gains control of the server, they could access, steal, or alter sensitive data transmitted over the network.
• Denial of Service: The vulnerability could be exploited to crash the DHCP Server, leading to network outages and preventing legitimate devices from obtaining IP addresses.

Given the CVSS base score of 9.8 (Critical), this vulnerability poses a high risk to organizations relying on Windows DHCP Server for network management.

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Compliance Impact

This vulnerability can impact compliance with several common standards and regulations, depending on the organization's environment and the data processed by the affected system:

• GDPR (General Data Protection Regulation): If the compromised DHCP Server handles or routes personal data of EU citizens, a successful exploit could lead to unauthorized access or exposure of this data. GDPR requires organizations to implement appropriate security measures to protect personal data, and a breach could result in significant fines or legal consequences.
• HIPAA (Health Insurance Portability and Accountability Act): For healthcare organizations, if the DHCP Server is part of a network that processes or transmits protected health information (PHI), exploitation of this vulnerability could lead to unauthorized access to PHI. This would constitute a breach under HIPAA, requiring notification and potentially resulting in penalties.
• PCI DSS (Payment Card Industry Data Security Standard): If the network managed by the DHCP Server processes payment card data, a compromise could lead to unauthorized access to cardholder data. PCI DSS requires strict security controls to protect such data, and a breach could result in non-compliance and financial penalties.
• NIST and Other Frameworks: Many compliance frameworks, such as NIST SP 800-53 or ISO 27001, require organizations to maintain the confidentiality, integrity, and availability of systems and data. A remote code execution vulnerability like this could violate these requirements, leading to non-compliance and potential audit failures.

Organizations should assess whether the affected DHCP Server processes or routes sensitive data and take immediate steps to mitigate the vulnerability to avoid compliance violations.

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Mitigation Strategies

To mitigate CVE-2026-56159, follow these immediate steps:

• Apply the latest security updates from Microsoft as soon as possible. The patch for this vulnerability is likely included in the latest cumulative update for Windows Server.
• If patching is not immediately feasible, consider disabling the DHCP Server service temporarily until the patch can be applied. This can be done via the Services management console (services.msc) or using the following PowerShell command: Stop-Service -Name DHCPServer.
• Restrict network access to the DHCP Server to trusted networks only. Use firewalls or network security groups to limit exposure to unauthorized networks.
• Monitor the DHCP Server for any signs of exploitation, such as unexpected crashes or unusual network activity.

For detailed mitigation steps, refer to Microsoft's official update guide for CVE-2026-56159.

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