Common Conditional Access policy: Block legacy authentication
Due to the increased risk associated with legacy authentication protocols, Microsoft recommends that organizations block authentication requests using these protocols and require modern authentication. For more information about why blocking legacy authentication is important, see the article How to: Block legacy authentication to Microsoft Entra ID with Conditional Access.
Organizations can choose to deploy this policy using the steps outlined below or using the Conditional Access templates.
Create a Conditional Access policy
The following steps will help create a Conditional Access policy to block legacy authentication requests. This policy is put in to Report-only mode to start so administrators can determine the impact they'll have on existing users. When administrators are comfortable that the policy applies as they intend, they can switch to On or stage the deployment by adding specific groups and excluding others.
- Sign in to the Microsoft Entra admin center as at least a Conditional Access Administrator.
- Browse to Protection > Conditional Access.
- Select Create new policy.
- Give your policy a name. We recommend that organizations create a meaningful standard for the names of their policies.
- Under Assignments, select Users or workload identities.
- Under Include, select All users.
- Under Exclude, select Users and groups and choose any accounts that must maintain the ability to use legacy authentication. Microsoft recommends you exclude at least one account to prevent yourself from being locked out.
- Under Target resources > Cloud apps > Include, select All cloud apps.
- Under Conditions > Client apps, set Configure to Yes.
- Check only the boxes Exchange ActiveSync clients and Other clients.
- Select Done.
- Under Access controls > Grant, select Block access.
- Select Select.
- Confirm your settings and set Enable policy to Report-only.
- Select Create to create to enable your policy.
After administrators confirm the settings using report-only mode, they can move the Enable policy toggle from Report-only to On.
Conditional Access policies are enforced after first-factor authentication is completed. Conditional Access isn't intended to be an organization's first line of defense for scenarios like denial-of-service (DoS) attacks, but it can use signals from these events to determine access.