In security, "fallback to insecure" is just "insecure with extra steps." Before you flip the switch to Level 2 across all your DCs, you need to audit your environment. Switching to Enforced will break authentication for any user or device that relies on weak certificate mapping.
Here is your 3-step migration plan:
Hardening Windows Authentication: A Deep Dive into StrongCertificateBindingEnforcement strongcertificatebindingenforcement
Look for (KDC_ERR_CERTIFICATE_MISMATCH) and Event ID 41 (Weak mapping fallback). These events tell you exactly which accounts will break when you enforce strong binding. In security, "fallback to insecure" is just "insecure
For years, most admins ignored it. But in 2024/2025, ignoring this setting is a security risk you cannot afford to take. These events tell you exactly which accounts will
Instead of just looking at the human-readable fields in the certificate, the DC now verifies a cryptographic link between the certificate and the user object in Active Directory. It checks the (or the entire certificate) against a value stored in the user’s msDS-KeyCredentialLink attribute.
In this post, we’ll break down what certificate binding is, how attackers bypass it, and why StrongCertificateBindingEnforcement = 2 (Enforced) is the new standard for authentication hardening. Windows uses a protocol called PKINIT to allow smart cards (or Windows Hello for Business) to authenticate to Active Directory. When a certificate is presented, the Domain Controller (DC) extracts the user’s identity from the certificate and maps it to an Active Directory account.