CVE-2026-77891 in Windows
Summary
by MITRE • 09/09/2026
Out-of-bounds read in Windows DHCP Server allows an authorized attacker to execute code locally.
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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 service represents a critical memory safety flaw that compromises the integrity and availability of network infrastructure services running on affected systems. This specific defect occurs when the DHCP server processes specially crafted packets or configuration data, leading to a scenario where the application attempts to access memory locations beyond the allocated buffer boundaries. While out-of-bounds reads are typically associated with information disclosure rather than direct code execution, in this context, the improper handling of these memory accesses can lead to undefined behavior that an attacker may exploit through sophisticated techniques such as heap spraying or specific timing attacks to achieve arbitrary code execution within the security context of the DHCP service account.
From a technical perspective, the flaw resides in how the DHCP server validates and parses incoming requests before processing them for lease assignment or configuration updates. The lack of rigorous bounds checking allows an attacker who has authenticated access to the network segment served by this DHCP server to trigger the erroneous memory read operation. This action can corrupt internal data structures or leak sensitive kernel-mode information, which serves as a stepping stone for further exploitation. The presence of such a vulnerability underscores the complexity and risk inherent in maintaining legacy networking services that handle high volumes of dynamic requests without sufficient modern security mitigations like Address Space Layout Randomization (ASLR) or Data Execution Prevention (DEP) being fully effective against this specific attack vector.
The operational impact of this vulnerability is severe, particularly for organizations relying on Windows-based DHCP servers to manage IP address allocation across their enterprise networks. An authorized attacker who successfully exploits this flaw can execute arbitrary code with the privileges of the DHCP service account, which often possesses significant permissions within the local system and potentially domain-wide if the server is configured as a primary or secondary DNS/DHCP node in an Active Directory environment. This level of access allows for lateral movement, privilege escalation to SYSTEM-level rights, installation of backdoors, exfiltration of network configuration data, and disruption of critical network connectivity services. The ability to execute code locally means that physical or logical access to the authenticated user account is sufficient to compromise the entire host machine and potentially the broader network infrastructure dependent on it.
This vulnerability aligns with Common Weakness Enumeration (CWE) category CWE-125, which describes Out-of-bounds Read, a flaw where software reads data past the end of a buffer or array. Furthermore, in terms of tactical classification under the MITRE ATT&CK framework, this exploit scenario relates to techniques involving Initial Access through valid accounts and subsequent Execution via local privilege escalation or service exploitation. The attack path typically involves gaining initial foothold credentials, interacting with the DHCP service interface, triggering the memory corruption event, and leveraging the resulting instability to inject and execute malicious payloads.
Mitigation strategies must prioritize immediate patching of all affected Windows systems using official security updates provided by Microsoft. Administrators should verify that the latest cumulative update for the specific version of Windows Server running the DHCP role is installed. In environments where patching cannot be immediately applied, network segmentation policies should be enforced to restrict access to the DHCP server ports from untrusted or less secure network zones. Additionally, implementing strict input validation and monitoring tools can help detect anomalous traffic patterns indicative of exploitation attempts. Regular auditing of service accounts and adherence to the principle of least privilege are essential long-term controls to minimize the blast radius in case a similar vulnerability is discovered in the future.