CVE-2026-69637 in Windows
Summary
by MITRE • 09/09/2026
Out-of-bounds read in Windows DHCP Server allows an authorized attacker to deny service over an adjacent network.
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Analysis
by VulDB Data Team • 09/09/2026
The vulnerability identified as an out-of-bounds read within the Microsoft Dynamic Host Configuration Protocol (DHCP) server represents a critical memory safety flaw that can be exploited by authenticated attackers to cause a denial of service against systems on adjacent networks. This specific defect arises from improper validation of input data during the processing of DHCP messages, specifically when handling certain malformed or excessively large packets. When the DHCP server processes these maliciously crafted requests, it attempts to access memory locations beyond the allocated buffer boundaries. While out-of-bounds reads typically result in information disclosure rather than code execution, in this specific context involving network services and protocol parsing logic, the primary consequence is a crash of the dhcpcore.dll process or the entire DHCP service, leading to immediate service disruption for clients relying on that server for IP address assignment and configuration parameters.
From a technical perspective, this flaw aligns with CWE-125, which describes out-of-bounds read vulnerabilities where software reads data past the end or before the beginning of the intended buffer. The attacker must possess valid credentials to interact with the DHCP service, as authentication is required to send requests that trigger the parsing logic containing the vulnerability. However, because DHCP operates at Layer 3 and relies on UDP traffic which can be spoofed if routing controls are lax, an authorized user or a compromised host within the same subnet could potentially leverage this flaw against other network segments depending on how relay agents and firewall rules are configured. The impact is localized to denial of service rather than privilege escalation or remote code execution, but the availability impact is severe for any organization dependent on automated IP address management.
The operational impact centers on the unavailability of DHCP services, which can halt new device onboarding and disrupt lease renewals for existing clients. In enterprise environments where dynamic addressing is critical for network scalability and security policy enforcement via Network Access Control (NAC) systems, such a disruption can lead to significant productivity losses and potential security gaps if devices are forced into static configurations or disconnected from the network entirely. The vulnerability affects multiple versions of Windows Server that include the DHCP role, making it relevant across various deployment scenarios including small business networks and large enterprise data centers.
Mitigation strategies primarily involve applying the latest cumulative updates provided by Microsoft to patch the underlying memory handling logic in the DHCP server components. Administrators should ensure that all servers running the DHCP service are updated promptly upon release of security patches addressing this issue. Additionally, network segmentation and strict access control lists can limit exposure by restricting which hosts or subnets can send DHCP requests to critical infrastructure servers. Implementing rate limiting on DHCP traffic and monitoring for anomalous packet sizes can also help detect attempted exploitation before a crash occurs. Security teams should monitor system logs for dhcpcore.dll crashes or service restarts as indicators of potential abuse attempts targeting this vulnerability.
This incident underscores the importance of rigorous input validation in network protocol implementations, even when access is restricted to authenticated users. It highlights how memory safety issues can still lead to significant availability impacts without requiring complex exploitation chains involving privilege escalation. Organizations should review their DHCP infrastructure for proper patch management and consider deploying intrusion detection systems capable of identifying malformed DHCP packets that exceed expected size limits or contain invalid structures indicative of fuzzing attacks targeting this specific flaw.