M365 Identity Device Code Grant with Unusual User and ASN

Description

Identifies a Microsoft 365 OAuth device code grant ("Cmsi:Cmsi") with application Microsoft Authentication Broker ("29d9ed98-a469-4536-ade2-f981bc1d605e") for Microsoft Graph from a source ASN not previously observed for that user in a historical window. Phishing kits leveraging device code phishing complete the full login (password and MFA) at the genuine Microsoft endpoint and harvest the resulting token by polling, so MFA does not stop them and the authorization commonly originates from attacker-controlled residential proxy or hosting infrastructure rather than the user's normal network.

Detection logic

Its licence does not clear it for publishing here

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Detection requirements

Platform: Containers ESXi IaaS Identity Provider Linux macOS Network Devices Office Suite SaaS Windows
The rule states no platform. This is derived from the 3 ATT&CK techniques it maps to.
Log source category: event_index

Known benign triggers

A user authenticating via the device code flow for the first time from a new but legitimate network, such as travel, a new home or office ISP, a corporate VPN, or a mobile carrier. Device code authentication is expected when enrolling or signing in on input-constrained devices (smart TVs, kiosks, IoT, conference room devices) and for some CLI or headless developer workflows. Review the source ASN, geolocation, and the user's prior device code history to confirm whether the origin is plausible before escalating.

References

Links the source published beside this detection. Reference is the link the source wrote, unmodified. Class is decided by this catalogue from the host and path, not stated by the source. Cited by counts published detections citing the same resource, including this one, and the sources beneath it count the repositories this catalogue ingests, which is not the same as independent research.
Reference	Class	Cited by
arcticwolf.com/resources/blog/kali365-expands-into-aws-microsoft-okta-xerox-max-messenger/	Unclassified	2
arcticwolf.com/resources/blog/token-bingo-dont-let-your-code-be-the-winner/	Unclassified	7
www.ic3.gov/PSA/2026/PSA260521	Unclassified	6
www.microsoft.com/en-us/security/blog/2025/02/13/storm-2372-conducts-device-code-phishing-campaign/	Threat report	4
www.volexity.com/blog/2025/02/13/multiple-russian-threat-actors-targeting-microsoft-device-code-authentication/	Threat report	5

Detection rules

M365 Identity Device Code Grant with Unusual User and ASN

Description

Detection logic

Detection requirements

Known benign triggers

MITRE ATT&CK mappings

References

From the source

Licence

Authorship

Detection rules