Suspicious Azure AD MFA Fatigue Repeated Push Denials

ATT&CK techniques

Cred Access

Recon
Resource Dev
Initial Access
Execution
Persistence
Priv Esc
Defense Evasion
Cred Access
- T1621Multi-Factor Authentication Request Generation
Discovery
Lateral Movement
Collection
C2
Exfiltration
Impact

What it detects

This rule detects Entra ID sign-in events with result code 500121, which records that a multifactor authentication request was denied by the user. A burst of these denials for a single userPrincipalName indicates an MFA fatigue or push-bombing attack where an adversary holding valid credentials repeatedly prompts the victim hoping for an accidental approval. This is important because sustained denials often precede a coerced approval and account takeover.

Reporting behind it

Related detections4 linkedT1621 — drag to rearrange

Suspicious Entra ID Device Code Flow Authentication

Suspicious AiTM Phishing Kit Session Validation Endpoint via Proxy

Azure Sign-in Logs: MFA Denied Based on Authentication Requirement

Azure Sign-in Log MFA Interrupted via Strong Auth Failures

Suspicious Azure AD MFA Fatigue Repeated Push Denials

Pivot detection · T1621 · 4 related

Detection content is published as a reviewed draft. Tune thresholds and exclusions against your own telemetry before enabling this rule for alerting.

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