Analysis
A forged token signed with the real key is not a break-in. It is a credential. The mechanism behind AD FS token forgery, what the DKM container protects, and what the October hardening can and cannot fix.
A Golden SAML token is a forged SAML response signed with the real key. It impersonates any user in a federated environment, and it passes because the services on the other end validate the signature, not the person. First reported by CyberArk in 2017, the technique reaches federated services such as email systems and APIs by exploiting the trust relationship between an identity provider and the services that rely on it. As documented in the Sygnia report, it gained its widest visibility during the SolarWinds software supply chain attack.
The mechanism runs on a specific chain of events. An adversary must first gain administrative access to the Active Directory Federation Services (AD FS) server. With that control established, the attacker extracts the token-signing certificate and its private key. That key forges SAML responses that look legitimate to any service configured to trust the environment’s identity provider. The forged tokens carry a valid signature from the stolen key, so relying parties accept them as authentic and grant access to hosted resources, including for data exfiltration.
Multi-factor authentication is bypassed because the authentication process is subverted before it begins. When an attacker presents a forged token, the relying party validates the signature against the trusted certificate. The signature is mathematically correct, so the service grants access without ever communicating with the AD FS server or the Domain Controller. Those systems never see the login attempt, and no authentication events or MFA triggers are recorded. The detection tell is therefore a successful federated login at a relying party with no corresponding authentication events at the identity provider or domain level.
The security of that key is tied to the Distributed Key Manager (DKM) container. Per Microsoft’s KB5121391 documentation, AD FS uses the DKM container to store the symmetric keys that protect the private keys of token-signing and token-encryption certificates. If the container’s access control list is overly permissive, an attacker with read access to the DKM key material can decrypt the token-signing private keys. That elevation-of-privilege issue is tracked in the CVE-2026-56155 record.
Microsoft’s hardening ran in phases. Audit mode arrived with the July 14, 2026 security update: the AD FS service checks the container ACL at startup and every 24 hours after, logging Event 1132 when the ACL misses the expected secure state. Enforcement became the default with the October 2026 update, as covered in our AD FS enforcement piece. The update remediates the ACL down to four principals: Domain Admins, Enterprise Admins, SYSTEM, and the AD FS service account. Inheritance is disabled and every other explicit access entry is removed. Windows Server 2012 and 2012 R2 are excluded from automatic remediation; those platforms harden manually, granting the AD FS service account WriteOwner and WriteDacl before opting in. For organizations that opt out of automatic remediation, Microsoft’s own documentation is blunt:
Opting out leaves your DKM container vulnerable. Only use this if you have a specific compatibility requirement and plan to manually harden the ACL.
The opt-out does not silence detection: Event 1132 keeps firing so the insecure state stays visible. What the hardening cannot do is invalidate keys already extracted. A token-signing private key taken before these controls remains valid for forging tokens, and Sygnia’s research puts the end of that access at a single point: the existing AD FS private key must be invalidated and replaced, which means altering or terminating connectivity to all federated systems and re-creating them. The signing key is the trust root. The October hardening narrows who can reach it; it cannot recall what was already taken.
Heath Callahan works for Forkast.
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