CVE-2026-69876 in Windows
Summary
by MITRE • 09/09/2026
Use after free in Windows DHCP Server allows an authorized attacker to execute code over an adjacent network.
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Analysis
by VulDB Data Team • 09/09/2026
The vulnerability identified as a use-after-free condition within the Microsoft Dynamic Host Configuration Protocol (DHCP) server service represents a critical memory corruption flaw that can be leveraged by authenticated attackers to achieve remote code execution. This specific class of vulnerabilities arises when software continues to use a pointer after it has been freed, leading to undefined behavior that often manifests as arbitrary write or read capabilities in the context of the vulnerable process. In this instance, the DHCP server service, which is responsible for automatically assigning IP addresses and other network configuration parameters to devices on an IPv4 network, contains logic errors during memory management operations. When a client sends specific crafted requests to the DHCP server, the application may deallocate certain data structures but retain references to them in subsequent processing steps. If these dangling pointers are accessed later, particularly if the underlying memory has been reallocated for different purposes by the operating system or other threads, an attacker can manipulate the contents of that memory region to control program flow.
From a technical perspective, this flaw falls squarely under CWE-416: Use After Free, which is categorized as a high-severity weakness in software security. The exploitation mechanism typically involves crafting malicious DHCP packets that trigger the premature deallocation of specific objects while keeping references alive within the server's internal state machine or callback structures. By carefully controlling what data is written into the freed memory block before it is accessed again, an attacker can overwrite function pointers, virtual table entries, or other control flow indicators. This allows for arbitrary code execution with the privileges of the DHCP service account, which on many Windows systems runs with high-level administrative rights to manage network configurations effectively. The ability to execute code remotely over a adjacent network highlights the severity of the issue, as it does not require physical access to the target machine or complex social engineering tactics beyond initial authentication credentials for the DHCP scope or lease management functions.
The operational impact of this vulnerability is severe, potentially leading to complete compromise of the affected Windows server and any systems reachable from that host. An attacker who successfully exploits this flaw gains full control over the operating system running on the target machine. This can result in the installation of malware, creation of backdoors for persistent access, exfiltration of sensitive data stored or processed by the DHCP service, and lateral movement within the enterprise network. Since DHCP is a foundational infrastructure service, compromising it can also disrupt network availability if the attacker chooses to degrade service rather than maintain stealthy access. Furthermore, because the vulnerability allows execution over an adjacent network, attackers positioned on the same subnet or connected via trusted routing policies can target this service without needing direct internet-facing exposure, making detection and prevention more challenging for perimeter-based security controls that do not inspect internal traffic thoroughly.
Mitigation strategies must focus on both immediate remediation and long-term architectural hardening. The primary defense is to apply the latest security updates provided by Microsoft as soon as they become available, ensuring that the memory management logic within the DHCP server service is patched against this specific use-after-free condition. Organizations should also enforce strict network segmentation policies to limit access to critical infrastructure services like DHCP from untrusted or general user subnets. Implementing deep packet inspection at network boundaries can help identify and block malformed packets attempting to exploit such vulnerabilities, although signature-based detection may lag behind zero-day exploits. Additionally, running the DHCP service under a least-privilege account rather than with full administrative rights can reduce the impact of successful exploitation by limiting the permissions available to any code executed within that process context. Regular auditing of network traffic and monitoring for anomalous behavior in system processes are also recommended practices to detect potential exploitation attempts early.