CVE-2026-77886 in Windows
Summary
by MITRE • 09/09/2026
Out-of-bounds read 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 described involves a critical out-of-bounds read flaw within the Dynamic Host Configuration Protocol (DHCP) server component of Microsoft Windows operating systems. This specific implementation error occurs when the DHCP service processes specially crafted network packets that trigger an incorrect memory access operation. Instead of validating the length or boundaries of incoming data structures before reading from them, the application attempts to retrieve information from a memory location that lies outside the allocated buffer space. This type of defect is fundamentally categorized under CWE-125, which defines out-of-bounds read vulnerabilities where software reads past the end of an intended buffer. The root cause typically stems from insufficient boundary checks during the parsing of DHCP message fields, allowing malformed packets to exploit the logic error and force the system to access unauthorized memory regions.
From a security perspective, this vulnerability is primarily exploitable for denial-of-service purposes rather than remote code execution or privilege escalation in its current manifestation. An attacker who can send network traffic to the vulnerable DHCP server does not require authentication, making it an unauthenticated attack vector. By sending specific malformed packets that trigger the out-of-bounds read condition, the attacker can cause the DHCP service process to crash or become unstable. This results in a complete loss of availability for IP address assignment services within the affected network segment. The operational impact is significant because modern enterprise networks rely heavily on automated IP configuration via DHCP; disrupting this service prevents new devices from connecting and existing clients from renewing their leases, effectively paralyzing network connectivity for users dependent on that specific server instance.
The attack vector aligns with MITRE ATT&CK technique T1498, which covers Network Denial of Service, specifically focusing on resource exhaustion or service disruption through protocol abuse. Since the vulnerability is triggered over the network without prior access to the system, it represents a high-risk threat for any DHCP server exposed to untrusted networks or even internal segments where malicious actors might reside. The lack of authentication requirement means that both external attackers and insider threats can leverage this flaw with minimal effort, provided they have basic network connectivity to the target host on UDP port 67.
Mitigation strategies must focus on immediate patching and network-level controls. Organizations should apply the latest security updates released by Microsoft for their Windows DHCP server roles as soon as possible. Until patches are applied, administrators can implement strict firewall rules or Access Control Lists (ACLs) to restrict access to UDP port 67 only from trusted subnets known to contain legitimate DHCP clients. Additionally, enabling logging on the DHCP service may help in detecting attempts to exploit this vulnerability by monitoring for unusual packet patterns or repeated connection failures originating from single sources. It is also advisable to segment critical infrastructure networks using VLANs and firewalls to limit the blast radius of such attacks should they occur. Regular network traffic analysis tools can be configured to flag malformed packets that exhibit characteristics consistent with buffer overflow attempts, providing an additional layer of defense in depth against this specific class of vulnerabilities.