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

Related detections9 linkedT1078.004 — drag to rearrange

Suspicious Flax Typhoon System Utility Masquerade Outside System32 via Renamed VPN Client (via process_creation)

Suspicious SES Account Sending Enablement and Identity Verification via CloudTrail

Possible Stolen AWS Credential Validation via STS GetCallerIdentity

Suspicious AWS Federated Console Login From Programmatic Credentials

Suspicious M365 Legacy Authentication via BAV2ROPC Client via m365

Suspicious STS AssumeRole With Exfil Session Name via CloudTrail (via cloudtrail)

Possible ReverseSocks5 Tunneling Tool Execution on Linux (via process_creation)

Suspicious AWS Console Login Without MFA

Suspicious Cloud Sign-In From an Anonymizer or High-Risk Session (via signinlogs)

Possible Credential Stuffing Blocked by Conditional Access in Microsoft 365

Pivot detection · T1078.004 · 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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