CVE-2026-77893 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 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 during its standard operational cycle, such as handling lease requests or renewals. The root cause lies in improper boundary checking within the code responsible for parsing incoming protocol messages. When an attacker sends a maliciously constructed packet to the vulnerable service, the application attempts to read memory locations that lie outside the allocated buffer boundaries. This action does not typically allow for arbitrary code execution due to the nature of a read operation rather than a write, but it inevitably triggers an access violation exception within the DHCP server process.
From a technical perspective, this flaw aligns with Common Weakness Enumeration (CWE) category CWE-125, which describes out-of-bounds read vulnerabilities where software reads data past the end or before the beginning of the intended buffer. The operational impact is primarily focused on service availability rather than confidentiality or integrity in most scenarios. When the exception occurs, the DHCP server process may crash and restart automatically if configured with high-availability features, leading to intermittent disruptions. However, without such safeguards, a single successful exploit can cause the DHCP service to stop responding entirely. This results in a denial of service condition where legitimate clients are unable to obtain IP address configurations or renew existing leases, effectively paralyzing network connectivity for devices relying on that specific server segment.
The attack vector is classified as remote and non-interactive, meaning an unauthorized attacker can trigger this vulnerability over the network without requiring prior authentication or user interaction. This significantly lowers the barrier for exploitation compared to vulnerabilities requiring local access. The threat actor only needs network reachability to the DHCP service port, typically UDP 67 or 68, to send the malformed packets that exploit the memory handling error. Consequently, this vulnerability poses a substantial risk in environments where the DHCP server is exposed to untrusted networks or lacks sufficient ingress filtering and rate limiting controls.
Mitigation strategies must focus on both immediate remediation and long-term architectural hardening. The primary defense is the timely application of security updates provided by Microsoft that patch the underlying memory handling logic within the DHCP service binaries. Organizations should verify their inventory for affected Windows server versions and prioritize patching based on exposure to external networks. In addition to patching, network-level controls such as Access Control Lists (ACLs) can be implemented to restrict access to the DHCP service ports only from trusted subnets or specific management stations. This limits the attack surface by preventing unauthorized hosts from sending crafted packets that could trigger the vulnerability. Furthermore, deploying intrusion detection systems with signatures for malformed DHCP traffic can help identify and block exploitation attempts in real-time.
In terms of threat intelligence frameworks, this vulnerability is relevant to MITRE ATT&CK techniques related to Denial of Service (T1499) and potentially Initial Access if used as a distraction or resource exhaustion tactic during broader attacks. While the primary outcome is service disruption, attackers may leverage such instability to mask other malicious activities or force administrators into reactive modes that reduce overall security posture. Therefore, treating this out-of-bounds read not just as an isolated bug but as part of a potential multi-stage attack strategy is essential for comprehensive defense. Regular vulnerability scanning and continuous monitoring of DHCP server logs for unusual error patterns are recommended practices to maintain resilience against such memory corruption exploits in enterprise network environments.