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Entra ID Conditional Access MFA Bypass with Unusual User, Client and Source ASN

Identifies the first observed instance of a Microsoft first-party public client application acquiring a Microsoft Graph token using single-factor (password-only) authentication while an MFA Conditional Access grant…

Description

Identifies the first observed instance of a Microsoft first-party public client application acquiring a Microsoft Graph token using single-factor (password-only) authentication while an MFA Conditional Access grant control went unenforced, for a given user, application, and source autonomous system (ASN). This pattern is associated with the Conditional Access "resource exclusion" bypass: when a tenant's "all resources" Conditional Access policy contains at least one application exclusion, Entra ID issues tokens for low-privilege baseline scopes (User.Read, openid, profile, email) to any resource, including Microsoft Graph, without enforcing the policy's grant controls (such as MFA). An adversary holding only a stolen password can therefore obtain a Graph token through a trusted first-party public client (for example, Microsoft Bing Search) and enumerate directory objects, even though the tenant requires MFA. Critically, the overall conditional_access_status is never "failure" for this technique (the sign-in is not blocked); it is reported as "success" or "notApplied" depending on what other policies exist in the tenant, so detections that key on Conditional Access failures will not observe it. The reliable fingerprint is in the per-policy results: a policy whose enforced grant control is MFA reports a result of "notApplied" for this sign-in, meaning the MFA requirement was silently not enforced while the single-factor, password-only sign-in still succeeded.

Detection logic

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Detection requirements

Platform
ContainersESXiIaaSIdentity ProviderLinuxmacOSNetwork DevicesOffice SuiteSaaSWindows

The rule states no platform. This is derived from the 2 ATT&CK techniques it maps to.

Log source category
event_index

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