Adversaries may disable or modify multi-factor authentication (MFA) mechanisms to enable persistent access to compromised accounts.
Once adversaries have gained access to a network by either compromising an account lacking MFA or by employing an MFA bypass method such as Multi-Factor Authentication Request Generation, adversaries may leverage their access to modify or completely disable MFA defenses. This can be accomplished by abusing legitimate features, such as excluding users from Azure AD Conditional Access Policies, registering a new yet vulnerable/adversary-controlled MFA method, or by manually patching MFA programs and configuration files to bypass expected functionality.
For example, modifying the Windows hosts file (
C:\windows\system32\drivers\etc\hosts) to redirect MFA calls to localhost instead of an MFA server may cause the MFA process to fail. If a "fail open" policy is in place, any otherwise successful authentication attempt may be granted access without enforcing MFA. 
Depending on the scope, goals, and privileges of the adversary, MFA defenses may be disabled for individual accounts or for all accounts tied to a larger group, such as all domain accounts in a victim's network environment.
Review MFA actions alongside authentication logs to ensure that MFA-based logins are functioning as intended.
Ensure that MFA and MFA policies and requirements are properly implemented for existing and deactivated or dormant accounts and devices. If possible, consider configuring MFA solutions to "fail closed" rather than grant access in case of serious errors.
|M1018||User Account Management||
Ensure that proper policies are implemented to dictate the secure enrollment and deactivation of MFA for user accounts.
|ID||Data Source||Data Component||Detects|
|DS0026||Active Directory||Active Directory Object Modification||
Monitor for changes made to AD security settings related to MFA logon requirements, such as changes to Azure AD Conditional Access Policies or the registration of new MFA applications.
|DS0028||Logon Session||Logon Session Creation||
Monitor for logon sessions for user accounts and devices that did not require MFA for authentication.
|DS0002||User Account||User Account Authentication||
Monitor for account authentications in which MFA credentials are not provided by the user account to the authenticating entity.
|User Account Modification||
Monitor for the enrollment of devices and user accounts with alternative security settings that do not require MFA credentials for successful logon.