CVE-2026-77498 in Windows
Summary
by MITRE • 09/08/2026
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 identified as an out-of-bounds read within the Microsoft Dynamic Host Configuration Protocol (DHCP) server represents a critical memory safety flaw that compromises the availability of network infrastructure services. This specific defect occurs when the DHCP server processes specially crafted packets or malformed data structures, leading to an attempt to access memory locations outside the intended buffer boundaries. In the context of Windows Server environments, the DHCP service is responsible for automatically assigning IP addresses and other network configuration parameters to devices on a local area network. When this component encounters input that triggers the out-of-bounds read condition, it fails to handle the error gracefully, resulting in an application crash or termination of the dhcpssrv.exe process. This behavior directly facilitates a denial of service attack, where an unauthorized attacker can disrupt network connectivity for all clients relying on the affected DHCP server without needing any prior authentication credentials.
From a technical perspective, this vulnerability is classified under CWE-125, which denotes Out-of-bounds Read. The root cause typically stems from insufficient validation of input data lengths or indices before accessing array elements or memory buffers within the DHCP protocol handler. When an attacker sends a maliciously constructed packet that exploits these boundary checks, the server attempts to read data from invalid memory addresses. Depending on the specific implementation details and the state of the system's memory at the time of exploitation, this can lead to immediate service termination due to access violations or general protection faults. The lack of robust bounds checking allows external actors to trigger this condition remotely over the network, making it a significant threat vector for attackers seeking to degrade organizational IT operations by taking down critical networking services.
The operational impact of this vulnerability is severe in environments where DHCP servers are central to network management. A successful exploitation results in the immediate unavailability of IP address assignment and related configuration services. This disruption prevents new devices from joining the network, causes existing clients to lose their lease renewals if they cannot communicate with a functioning server, and can lead to widespread connectivity issues across subnets managed by the compromised service. For organizations that rely on automated provisioning or have limited static IP allocation capabilities, this denial of service effectively halts normal business operations related to network access. Furthermore, repeated exploitation attempts may cause instability in other dependent services if they share resources with the DHCP server process, amplifying the scope of the disruption beyond just address assignment failures.
Mitigation strategies for this vulnerability primarily involve applying the relevant security updates provided by Microsoft that patch the underlying memory handling logic within the DHCP service components. Administrators should ensure that all Windows Server systems running the DHCP role are updated to versions containing these fixes as a priority action. In addition to software patches, network-level defenses such as Access Control Lists (ACLs) on firewalls or routers can be configured to restrict access to UDP ports 67 and 68, which are used by DHCP, limiting exposure only to trusted subnets where legitimate clients reside. This reduces the attack surface available to remote attackers who might attempt to exploit this flaw from outside the local network segment. Continuous monitoring of system logs for unexpected service restarts or error events related to dhcpssrv.exe can also aid in detecting potential exploitation attempts before they cause prolonged outages.
This vulnerability aligns with MITRE ATT&CK technique T1499, Endpoint Denial of Service, specifically under the sub-technique of resource exhaustion through application crashes. By targeting a core infrastructure service like DHCP, attackers aim to degrade the availability component of the CIA triad without necessarily compromising data confidentiality or integrity. The nature of this flaw highlights the importance of rigorous input validation and memory safety practices in network protocol implementations. As organizations continue to modernize their IT infrastructure, ensuring that foundational services are hardened against such common programming errors remains essential for maintaining resilient and reliable network operations. Regular vulnerability assessments and adherence to security patching schedules are critical defenses against exploiting these types of out-of-bounds access vulnerabilities in enterprise Windows environments.