CVE-2026-83511 in Active Directory Federation Services
Summary
by MITRE • 10/14/2026
Weak authentication in Active Directory Federation Services (AD FS) allows an unauthorized attacker to perform spoofing over a network.
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Analysis
by VulDB Data Team • 10/14/2026
Active Directory Federation Services serves as a critical component for implementing single sign-on and identity federation across enterprise environments, relying heavily on secure token issuance protocols such as SAML 2.0 and WS-Federation. The identified vulnerability represents a fundamental weakness in the authentication validation logic within AD FS, specifically concerning how service provider claims are verified against trusted issuers. This flaw allows an unauthorized attacker to exploit misconfigurations or inherent protocol ambiguities to bypass standard authentication checks, effectively enabling session spoofing over network connections. By manipulating the metadata exchange process or exploiting weaknesses in certificate validation during token consumption, an adversary can forge valid security tokens that appear to originate from a legitimate identity provider.
The technical nature of this flaw centers on insufficient verification of cryptographic signatures and issuer identities within incoming federation requests. In many implementations, AD FS may accept tokens where the signing certificate has not been rigorously validated against the organization's trusted root store or where the expected audience URI is not strictly enforced. This lack of strict binding between the token signature, the issuing identity provider, and the relying party allows attackers to inject forged claims into an active session. The attacker does not necessarily need valid credentials for a specific user account; instead, they leverage the trust relationship established by the federation infrastructure itself to impersonate legitimate users or services. This is particularly dangerous in hybrid cloud environments where on-premises Active Directory identities are federated with Azure AD or other external identity sources.
The operational impact of this vulnerability is severe, as it directly compromises the integrity of access control mechanisms across integrated applications and resources. Once an attacker successfully spoofs a valid authentication token, they gain unauthorized access to sensitive data, administrative consoles, and internal services that rely on federated identities for authorization decisions. This can lead to full account takeover, lateral movement within the network, and potential exfiltration of confidential information. Furthermore, because AD FS often acts as the gateway for privileged accounts and service-to-service communications, compromising this component provides a high-value entry point for advanced persistent threats seeking long-term access without triggering traditional perimeter security alerts.
From an industry standards perspective, this vulnerability aligns with CWE-287 Improper Authentication, where the system fails to correctly verify credentials or identity assertions before granting access. It also relates closely to CWE-345 Insufficient Verification of Data Authenticity, as the core issue lies in the failure to validate the integrity and origin of security tokens. In terms of MITRE ATT&CK mapping, this behavior corresponds to T1606 Forged Identity Tokens, which describes techniques where attackers create fake identity tokens to bypass authentication mechanisms. Additionally, it may involve elements of T1558 Steal or Forge Kerberos Tickets if the federation service interacts with on-premises kerberos infrastructure for legacy application support, although the primary vector here is web-based token forgery.
Mitigation strategies must focus on hardening the configuration of AD FS and enforcing strict validation policies. Administrators should ensure that all relying party trusts are configured to require specific claim rules that validate issuer signatures against known, trusted certificates only. It is essential to disable any legacy protocols or configurations that allow for weaker cryptographic algorithms such as SHA-1 signing if stronger alternatives like SHA-256 are supported and deployed across the identity infrastructure. Regular audits of federation metadata should be conducted to remove unused trusts and verify that certificate chains are complete and valid. Furthermore, implementing multi-factor authentication at the edge before tokens are issued can add a layer of defense-in-depth, ensuring that even if token forgery is attempted, the underlying user session requires additional proof of identity. Keeping AD FS servers updated with the latest cumulative updates from Microsoft is also critical to address known implementation flaws in protocol handling logic.