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Exchange must have Forms-based Authentication disabled.


Finding ID Version Rule ID IA Controls Severity
V-69719 EX13-CA-000015 SV-84341r2_rule Medium
Identification and Authentication provide the foundation for access control. Access to email services applications in the DoD requires authentication using DoD Public Key Infrastructure (PKI) certificates. Authentication for Outlook Web App (OWA) is used to enable web access to user email mailboxes and should assume that certificate-based authentication has been configured. This setting controls whether forms-based logon should be used by the OWA website. Because the DoD requires Common Access Card (CAC)-based authentication to applications, OWA access must be brokered through an application proxy or other pre-authenticator, which performs CAC authentication prior to arrival at the CA server. The authenticated request is then forwarded directly to OWA, where authentication is repeated without requiring the user to repeat authentication steps. For this scenario to work, the Application Proxy server must have forms-based authentication enabled, and Exchange must have forms-based Authentication disabled. If forms-based Authentication is enabled on the Exchange CA server, it is evidence that the application proxy server is either not correctly configured, or it may be missing.
MS Exchange 2013 Client Access Server Security Technical Implementation Guide 2019-12-18


Check Text ( C-70161r1_chk )
Open the Exchange Management Shell and enter the following command:

Get-OwaVirtualDirectory | Select ServerName, Name, Identity, FormsAuthentication

If the value of FormsAuthentication is not set to False, this is a finding.
Fix Text (F-75923r1_fix)
Open the Exchange Management Shell and enter the following command:

Set-OwaVirtualDirectory -Identity <'IdentityName'> -FormsAuthentication $false

Note must be in quotes.

Example for the Identity Name: \owa (Default Web site)

Restart the ISS service.