CVE-2026-69416 in Windows
Summary
by MITRE • 09/09/2026
Buffer over-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 a buffer over-read within the Microsoft Dynamic Host Configuration Protocol (DHCP) server represents a significant security risk that compromises the availability of critical network infrastructure services. This flaw resides specifically in how the DHCP server processes incoming requests, particularly those involving malformed or excessively large packets. When an attacker sends a specially crafted packet to the affected system, the application fails to properly validate the length of the input data against the allocated buffer size. Consequently, the software reads beyond the boundaries of the intended memory region, accessing adjacent memory locations that contain sensitive operational data or control structures. This out-of-bounds read operation disrupts the normal execution flow of the DHCP service, often leading to a crash or an unstable state from which the server cannot automatically recover without manual intervention.
From a technical perspective, this issue is classified under CWE-126, which denotes Buffer Over-read, indicating that the software reads data past the end, or before the beginning, of the intended buffer. The vulnerability leverages the fact that network services like DHCP are designed to handle variable-length inputs and must parse complex packet structures containing options and parameters. If the parsing logic does not strictly enforce bounds checking on these fields, an attacker can exploit this weakness by constructing a request where specific option values exceed expected limits. Although the primary consequence described is denial of service rather than arbitrary code execution or information disclosure, the mechanism relies on memory corruption principles similar to those found in more severe vulnerabilities. The impact is localized to the availability of IP address assignment and related network configuration services for clients connected to the adjacent network segment where the vulnerable server resides.
The operational impact of this vulnerability extends beyond a simple service interruption. DHCP servers are foundational components of most enterprise networks, responsible for dynamically assigning Internet Protocol (IP) addresses and other configuration parameters such as subnet masks, default gateways, and DNS server information. A successful exploitation results in the unavailability of these services, effectively isolating clients from network resources that rely on automatic configuration. In environments where static IP assignments are not feasible or practical due to scale or mobility requirements, this denial of service can halt business operations entirely for affected users. Furthermore, because DHCP operates at Layer 3 of the OSI model and interacts with lower-level networking protocols, a compromised server may also disrupt related services such as BOOTP compatibility features or relay agent functionalities if they are enabled on the same instance.
In terms of threat modeling and attack classification, this vulnerability aligns with MITRE ATT&CK technique T1498, specifically Network Denial of Service, which involves overwhelming network resources to make them unavailable to intended users. The attacker requires authorized access or proximity to the adjacent network segment to deliver the malicious payload, suggesting that lateral movement or initial compromise may be prerequisites depending on the specific deployment architecture and firewall rules. While the prompt specifies an authorized attacker, in many real-world scenarios, DHCP servers are exposed to untrusted networks via relay agents, potentially widening the attack surface if proper segmentation is not enforced. The ability to trigger a denial of service from adjacent network space highlights the importance of securing internal routing boundaries and ensuring that critical infrastructure services are protected against both external and insider threats.
Mitigation strategies for this vulnerability primarily involve applying vendor-provided security patches as soon as they become available, which typically include fixes to the input validation logic within the DHCP server component. Until patching is implemented, administrators should consider implementing network-level controls such as Access Control Lists (ACLs) on routers and switches to restrict access to the DHCP service port from untrusted or non-essential subnets. Rate limiting mechanisms can also be deployed at the network perimeter to detect and drop anomalous traffic patterns that resemble buffer overflow attempts. Additionally, ensuring that the DHCP server is hosted in a dedicated management VLAN with strict egress and ingress filtering reduces the likelihood of exploitation by unauthorized entities. Regular monitoring for service restarts or performance degradation on DHCP servers can aid in early detection of attempted exploits, allowing security teams to respond before significant operational disruption occurs.