CVE-2026-83645 in Active Directory Federation Services
Summary
by MITRE • 10/14/2026
Allocation of resources without limits or throttling in Active Directory Federation Services (AD FS) 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 within Active Directory Federation Services represents a critical flaw related to the improper allocation and management of system resources, specifically categorized under CWE-770: Allocation of Resources Without Limits or Throttling. This architectural deficiency allows an unauthorized attacker to consume excessive computational, memory, or network bandwidth resources by sending specially crafted requests that trigger disproportionate resource consumption on the server side. In the context of AD FS, which serves as a central identity provider for enterprise single sign-on and federated authentication scenarios, such unthrottled processing can lead directly to service degradation or complete denial of service conditions. The flaw exploits the lack of input validation limits and rate limiting mechanisms that should normally constrain the complexity and volume of requests processed during authentication flows, token generation, or metadata retrieval operations.
From an operational perspective, this vulnerability enables remote attackers who possess valid network access but not necessarily authenticated credentials to disrupt critical identity infrastructure services. By exploiting this weakness, an attacker can execute a denial-of-service attack that impacts all users relying on the AD FS server for accessing internal and external applications. This disruption compromises the availability pillar of the CIA triad, which is fundamental to enterprise security posture. The impact extends beyond simple downtime; it can hinder incident response capabilities during active attacks if identity services are unavailable, thereby masking other malicious activities within the network environment. Furthermore, because AD FS often handles sensitive authentication tokens and user session data, prolonged unavailability forces organizations into emergency recovery modes that may involve restoring from backups or switching to secondary systems, incurring significant operational costs and potential data integrity risks during failover procedures.
This type of vulnerability aligns with several tactics within the MITRE ATT&CK framework, particularly those related to Impact and Resource Hijacking. Attackers often leverage resource exhaustion techniques as a precursor to other attacks or as an independent act of disruption for competitive advantage or malicious intent. The specific technique involves overwhelming target resources through excessive requests, which falls under categories such as Denial of Service: Network Service Exhaustion or Application Layer Protocol Exploitation depending on the exact vector used within the AD FS protocol stack. Understanding this mapping helps security teams prioritize detection rules and monitoring strategies to identify anomalous traffic patterns indicative of resource exhaustion attempts before they cause significant service interruption.
Mitigation for this vulnerability requires a multi-layered approach focusing on both immediate remediation and long-term architectural hardening. Microsoft has released specific updates and patches that address the underlying code flaws responsible for unbounded resource allocation; applying these security updates is the primary corrective action. Additionally, organizations should implement network-level controls such as rate limiting at load balancers or web application firewalls to restrict the number of requests a single IP address can make within a given time frame. Configuring AD FS service parameters to enforce stricter timeouts and connection limits can also help mitigate the impact of excessive resource consumption. Regular security assessments, including penetration testing focused on availability threats, should be conducted to ensure that new configurations do not reintroduce similar weaknesses. Maintaining up-to-date documentation of all identity infrastructure components and their associated patch levels is essential for sustaining a resilient defense against such exploitation attempts.