CVE-2026-83665 in Windows
Summary
by MITRE • 10/14/2026
Null pointer dereference in Windows DHCP Server allows an unauthorized attacker to deny service over a network.
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Analysis
by VulDB Data Team • 10/14/2026
The vulnerability identified involves a null pointer dereception within the Dynamic Host Configuration Protocol (DHCP) server component of Microsoft Windows operating systems. This specific flaw arises when the software fails to properly validate input data before attempting to access memory addresses associated with pointers that have not been initialized or have been explicitly set to zero. In standard programming practices, accessing a null pointer leads to an immediate exception because the application attempts to read from or write to a memory location that is reserved and inaccessible for general use. This type of error represents a fundamental failure in input validation logic within the DHCP service handler, where specific malformed network packets can trigger this condition during routine processing operations.
From a technical perspective, this issue falls under the category of CWE-476, which denotes NULL Pointer Dereference. The root cause lies in the absence of sufficient boundary checks or nullity verification before dereferencing pointers derived from incoming DHCP messages. When an attacker crafts and transmits specially designed packets to the vulnerable DHCP server, the service attempts to process these inputs without confirming that all required data structures are validly allocated. Consequently, the operating system's exception handler intercepts this illegal memory access event, resulting in a crash of the dhcpcore.dll module or the entire DHCP Server service depending on the specific version and configuration context.
The operational impact of this vulnerability is primarily centered around denial of service rather than remote code execution or privilege escalation. An unauthorized attacker located anywhere on the network can exploit this flaw by sending maliciously crafted packets to port 67, which is the standard UDP port used for DHCP server communication. Upon receiving these packets, the DHCP server process terminates unexpectedly, causing a disruption in IP address assignment and lease management services for clients relying on that specific server. This results in a temporary loss of network connectivity for devices dependent on automatic configuration via DHCP until the service is manually restarted or automatically recovered by system monitoring tools if configured to do so.
This attack vector aligns with MITRE ATT&CK technique T1499, specifically Endpoint Denial of Service, as it involves overwhelming or crashing a specific endpoint component to degrade availability. It also relates to CWE-20, Improper Input Validation, highlighting the systemic weakness in how external data is processed before being utilized by core system functions. The severity of this vulnerability is typically rated as medium due to its impact on availability rather than confidentiality or integrity, although it can be critical if the DHCP server hosts a large number of clients and no redundant failover mechanisms are in place.
Mitigation strategies for this vulnerability primarily involve applying the relevant security updates provided by Microsoft that patch the underlying code flaw within the DHCP service logic. Administrators should ensure that all Windows servers running the DHCP role have received the latest cumulative updates addressing CVE identifiers associated with null pointer dereferences in network services. Additionally, implementing network segmentation and firewall rules can help restrict access to port 67 from untrusted networks, thereby reducing the attack surface available to potential adversaries. Monitoring logs for unexpected service restarts or exceptions related to dhcpcore.dll can also aid in detecting exploitation attempts before they cause significant operational disruption.