Possible Credential Stuffing Blocked by Conditional Access in Microsoft 365

ATT&CK techniques

Initial Access → C2

Recon
Resource Dev
Initial Access
- T1078.004Cloud Accounts
Execution
Persistence
- T1078.004Cloud Accounts
Priv Esc
- T1078.004Cloud Accounts
Defense Evasion
- T1078.004Cloud Accounts
Cred Access
- T1110.004Credential Stuffing
Discovery
Lateral Movement
Collection
C2
- T1090Proxy
Exfiltration
Impact

What it detects

This rule detects Microsoft 365 sign-in events blocked by Conditional Access after a valid password was supplied, which can indicate credential stuffing or password spraying against accounts protected only by MFA. Huntress observed adversaries validating stolen credentials from VPN, Tor, and proxy sources before attempting session takeover. A spike of these blocks from anomalous geographies surfaces pre-MFA account compromise that would otherwise be silent.

Reporting behind it

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Possible Credential Stuffing Blocked by Conditional Access in Microsoft 365

Pivot detection · T1090 · 9 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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