CVE-2026-77888 in Windows
Summary
by MITRE • 09/09/2026
Access of resource using incompatible type ('type confusion') in Windows DHCP Server allows an unauthorized attacker to deny service over a network.
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Analysis
by VulDB Data Team • 09/09/2026
The vulnerability identified involves a critical logic error within the Dynamic Host Configuration Protocol server component of Microsoft Windows, specifically manifesting as a type confusion flaw. This architectural defect arises when the system incorrectly interprets or handles data types during the processing of DHCP messages. In normal operation, the DHCP service manages network configuration parameters for clients requesting IP addresses and related settings. However, due to this incompatibility in type handling, an attacker who can communicate with the vulnerable server over a network is able to inject specially crafted packets that exploit this misinterpretation. The core technical flaw lies in the failure of the application to properly validate or cast data structures before processing them, leading to memory corruption or logical inconsistencies within the service's execution context.
From an operational perspective, the primary impact of this vulnerability is a denial of service condition. Because the type confusion occurs during the handling of incoming network requests, it causes the DHCP server process to become unstable and subsequently crash. This results in the immediate unavailability of IP address assignment services for devices on the local network segment. Unlike vulnerabilities that allow for remote code execution or privilege escalation, this specific flaw does not provide an attacker with a foothold within the system's security boundary but rather serves as a mechanism to disrupt critical infrastructure services. The availability of the DHCP service is essential for most enterprise networks, and its compromise effectively halts new device onboarding and can cause connectivity issues for existing clients depending on lease renewal timing.
This vulnerability aligns closely with CWE-843, which describes access of resource using incompatible type, commonly known as a type confusion error. It also maps to the MITRE ATT&CK framework under techniques related to service disruption or denial of service attacks against network services. The exploitation vector is typically remote if the DHCP server is exposed to untrusted networks, although it often requires local network access unless specific routing configurations expose the UDP port 67 interface externally. Security analysts should note that while this does not compromise confidentiality or integrity directly, its impact on availability makes it a significant risk for organizations relying heavily on automated IP management.
Mitigation strategies primarily involve applying vendor-supplied security patches as soon as they become available to address the underlying code defect in the DHCP server component. In environments where immediate patching is not feasible due to operational constraints or testing requirements, network segmentation should be employed to restrict access to UDP port 67 from untrusted zones. Additionally, implementing ingress filtering and monitoring for anomalous DHCP traffic patterns can help detect exploitation attempts early. Organizations must also ensure that their incident response plans account for potential disruptions in IP address allocation services, including manual fallback procedures for critical infrastructure devices during such outages. Regular auditing of network configurations to prevent unnecessary exposure of DHCP servers is a recommended long-term defensive posture against this class of vulnerabilities.