Name: OAuth Device Code Phishing via Auth Broker
Id: 14ce87d0-f7e7-40bc-94c3-c9f06188ee8e
MitreIds:
- T1550.001
Tactics:
- Defense Evasion
Techniques:
- 'Use Alternate Authentication Material: Application Access Token'
DetectionPriority: HIGH
ThreatPrevalence: MEDIUM
DetectionDifficulty: LOW
Description: >
  Adversaries abuse the OAuth 2.0 device authorization grant flow to obtain
  Microsoft access and refresh tokens without a credential-harvest page or
  MFA bypass. The attacker initiates a device code using the Microsoft
  Authentication Broker (MAB) app (client ID 29d9ed98-a469-4536-ade2-f981bc1d605e),
  then social-engineers the victim to enter the code at microsoft.com/devicelogin,
  presenting it as a "verification code" or MFA prompt. The completed flow yields
  access and refresh tokens scoped to the Auth Broker FOCI (Family of Client IDs)
  family, granting access to Exchange, Graph, SharePoint, and Teams without
  requiring the victim to visit a fake login page. The MAB app ID is hardcoded
  in Tycoon 2FA's device-code-grant variant and generates a distinctive
  authenticationProtocol: deviceCode signal in Entra ID sign-in logs on a
  first-party app ID rarely used interactively by end users.

LastUpdated: '2026-05-29'
Author: '@iimp0ster'

Prerequisites:
- Attacker can deliver a lure to the victim (email, Teams message, embedded link)
  that presents a device code as a legitimate verification prompt
- Target must have a Microsoft 365 / Entra ID account
- Tenant must not have a Conditional Access policy blocking device code flows
  (CA policy "Block device code flow" returns error 53003)
- Attacker must be able to poll oauth2/token until victim redeems the code

Chokepoints:
- Stage: Device Code Redemption via MAB App
  Input: Victim has entered the device code at microsoft.com/devicelogin
  Invariant: >
    The attacker MUST use a specific OAuth application to initiate the
    device code flow - Tycoon 2FA hardcodes the Microsoft Authentication Broker
    (client ID 29d9ed98-a469-4536-ade2-f981bc1d605e). Redemption generates an
    interactive sign-in event with authenticationProtocol: deviceCode and the MAB
    app ID, regardless of how the code was delivered to the victim.
  Observable: >
    Entra ID SigninLogs: authenticationProtocol == "deviceCode" AND
    appId == "29d9ed98-a469-4536-ade2-f981bc1d605e" AND
    resultType == "0" AND isInteractive == true.
    End users rarely initiate device-code flows to the Auth Broker interactively
    in managed environments - this combination is low-FP.
  WhyCantBypass: >
    The FOCI token chain required for Exchange/Graph/SharePoint/Teams access
    depends on the Auth Broker app ID. Using a different app ID would require
    re-engineering the token exchange chain and would break the downstream
    FOCI inheritance that makes the technique valuable. The authenticationProtocol:
    deviceCode field is set server-side by Microsoft when the device-code grant
    type is used - the attacker cannot change this to appear as a different flow.
  LogSources:
  - Entra ID Sign-in Logs (SigninLogs table in Sentinel)
  - Entra ID Interactive User Sign-In Logs
  DetectionTier: Analyst
  SigmaRef: sigma-rules/oauth-device-code-phishing/analyst.yml

- Stage: Token Inheritance via FOCI
  Input: Kit has obtained Auth Broker refresh token; begins accessing M365 resources
    via FOCI token exchange
  Invariant: The attacker MUST exchange the Auth Broker refresh token for access
    tokens to other M365 services via FOCI - generating non-interactive sign-in
    records on Exchange, Graph, SharePoint, and Teams from a cloud-VPS ASN
    within 10-20 minutes of the device-code completion event.
  Observable: >
    Entra ID NonInteractiveUserSignInLogs: Multiple resource sign-ins
    (Exchange, Graph, SharePoint, Teams) from cloud-VPS ASN within 10-20 minutes
    of the device-code interactive sign-in event for same UPN.
    incomingTokenType: refreshToken → primaryRefreshToken progression in
    Graph Activity Logs.
  WhyCantBypass: >
    Access to M365 resources requires valid tokens, which require token exchange
    calls that generate non-interactive sign-in log entries. The FOCI token
    exchange is the only mechanism to access multiple M365 resources from a
    single Auth Broker refresh token.
  LogSources:
  - Entra ID NonInteractiveUserSignInLogs
  - Microsoft Graph Activity Logs
  DetectionTier: Hunt
  SigmaRef: sigma-rules/oauth-device-code-phishing/hunt.yml

Variations:
- Name: Tycoon 2FA - Device Code Grant Variant
  FirstSeen: 2024-Q1
  Status: Active
  SourceURL: https://www.elastic.co/security-labs/tycoon-2fa-aitm-detection-engineering
  Notes: >
    Post-takedown adaptation by Tycoon 2FA operators. Device code delivered as
    "verification code" lure exploiting victim familiarity with MFA prompts.
    MAB client ID 29d9ed98-a469-4536-ade2-f981bc1d605e hardcoded. Token
    progression: incomingTokenType none → refreshToken → (optional) Rogue Device
    Registration → primaryRefreshToken. Bypasses URL-filtering defenses entirely
    - no phishing page to block.
  VariantId: tycoon-2fa-device-code
  Command:
    Invocation: |
      # Step 1: Request device code using MAB app
      POST https://login.microsoftonline.com/common/oauth2/v2.0/devicecode
        client_id=29d9ed98-a469-4536-ade2-f981bc1d605e
        scope=https://graph.microsoft.com/.default
      # Returns: device_code (shown to victim as "verification code"), user_code

      # Step 2: Poll until victim redeems code at microsoft.com/devicelogin
      POST https://login.microsoftonline.com/common/oauth2/token
        grant_type=urn:ietf:params:oauth:grant-type:device_code
        device_code=<device_code>
        client_id=29d9ed98-a469-4536-ade2-f981bc1d605e
      # Polls until resultType "0" - victim has entered code

      # Step 3: FOCI token exchange to access M365 resources
      POST https://login.microsoftonline.com/common/oauth2/token
        grant_type=refresh_token
        refresh_token=<mab_refresh_token>
        resource=https://outlook.office365.com  # Exchange
        client_id=29d9ed98-a469-4536-ade2-f981bc1d605e
    Context: >
      Variant bypasses credential-harvest detection (no fake login page).
      Code delivered via email lure as "verification code". Operators post-
      takedown combined device-code tradecraft with AiTM WebSocket relay.
    Artifacts:
    - 'Entra ID SigninLogs: authenticationProtocol "deviceCode" appId "29d9ed98-..." resultType "0" isInteractive "true"'
    - 'Entra ID NonInteractiveUserSignInLogs: FOCI token exchanges to Exchange/Graph/SharePoint from cloud-VPS ASN'
    - 'Graph Activity Logs: incomingTokenType progression none → refreshToken → primaryRefreshToken'
  ChokepointMapping: >
    Kit requests device code → lure delivers code to victim → victim redeems at
    devicelogin (interactive sign-in event: deviceCode + MAB app ID) → kit polls
    and receives tokens → FOCI exchange to M365 resources

EvolutionTimeline:
- Date: 2024-Q1
  Event: Tycoon 2FA operators adopt device-code-grant phishing post-takedown
  Change: >
    Following infrastructure disruptions, Tycoon 2FA operators adapt by combining
    AiTM tradecraft with OAuth device-code-grant phishing. The device-code variant
    bypasses URL-filtering defenses (no phishing page) and is harder to detect
    via traditional email scanning. MAB app ID hardcoded, generating a reliable
    detection signal.
  DetectionImpact: >
    URL-based phishing detection insufficient for device-code variant. authenticationProtocol:
    deviceCode on MAB app ID becomes the primary detection signal. CA policy
    "Block device code flow" (error 53003) provides prevention. Tenant admins
    should audit frequency of interactive device-code flows - most managed users
    never initiate them.
  TheConstant: "authenticationProtocol: deviceCode + MAB app ID + resultType 0 on interactive sign-in"
  Variants: []
  EventType: event

Detections:
- Level: Research
  Description: >
    Log all successful device-code-flow sign-ins regardless of app ID.
    Baseline for understanding legitimate device-code usage in the tenant.
  LogSources:
  - Entra ID Sign-in Logs
  Logic: >
    authenticationProtocol == "deviceCode" AND resultType == "0".
    No app filter. Run for one week to identify legitimate IoT devices,
    CLI tools (Azure CLI uses device code), and admin tooling.
  ExpectedFPRate: Medium (Azure CLI, VS Code Azure extension, IoT device enrollment)
  UseCase: >
    Baseline device-code flow volume and identify legitimate sources
    (Azure CLI, VS Code). Build exclusion list for analyst-tier rule.
  SigmaRule: sigma-rules/oauth-device-code-phishing/research.yml

- Level: Hunt
  Description: >
    Device-code flow on the Microsoft Authentication Broker app ID - rarely
    used interactively by end users in managed environments.
  LogSources:
  - Entra ID Sign-in Logs
  Logic: >
    authenticationProtocol == "deviceCode" AND
    appId == "29d9ed98-a469-4536-ade2-f981bc1d605e" AND
    resultType == "0". Alert on any occurrence - MAB app ID + device code
    interactive sign-in is low-volume and should be reviewed.
  ExpectedFPRate: Low (legitimate MAB device-code in managed device enrollment; rare)
  UseCase: >
    Active hunting. MAB app ID + device-code combination is low-FP in
    most enterprise tenants. Investigate each occurrence.
  SigmaRule: sigma-rules/oauth-device-code-phishing/hunt.yml

- Level: Analyst
  Description: >
    MAB device-code flow + isInteractive flag confirms victim redemption.
    High-confidence phishing indicator in managed tenants.
  LogSources:
  - Entra ID Sign-in Logs
  Logic: >
    authenticationProtocol == "deviceCode" AND
    appId == "29d9ed98-a469-4536-ade2-f981bc1d605e" AND
    resultType == "0" AND isInteractive == true.
    Exclude known-legitimate automation (document per tenant).
  ExpectedFPRate: Very Low
  UseCase: >
    SOC alerting. Immediate investigation. Trigger: enumerate registered devices,
    review recent sign-ins, revoke if confirmed phishing.
  SigmaRule: sigma-rules/oauth-device-code-phishing/analyst.yml

Intel:
- Name: Elastic Security Labs - Tycoon 2FA AiTM Detection Engineering
  Tier: primary
  URL: https://www.elastic.co/security-labs/tycoon-2fa-aitm-detection-engineering
  Description: >
    Primary source. MAB client ID (29d9ed98-a469-4536-ade2-f981bc1d605e) documented.
    Token progression (none → refreshToken → PRT) documented in Graph Activity Logs.
    CA policy mitigation (Block device code flow → error 53003) confirmed.

- Name: MITRE ATT&CK - T1550.001 Use Alternate Authentication Material
  Tier: primary
  URL: https://attack.mitre.org/techniques/T1550/001/
  Description: Primary technique definition.

RelatedChokepoints:
- aitm-websocket-relay
- aitm-device-prt-enrollment

KnownBypasses:
- Bypass: Using a different OAuth app ID (not MAB)
  Mitigation: Audit all app IDs used in device-code flows; alert on any
    non-allow-listed app ID initiating device code
  Detection: >
    Research-tier rule catches all device-code flows. Review any non-Azure CLI
    / non-VS Code app ID initiating device codes. The FOCI token chain restricts
    which app IDs are useful for broad M365 access.

- Bypass: Blocking CA policy not deployed (device code flows allowed)
  Mitigation: Deploy CA policy "Block device code flow" as a preventive control
  Detection: >
    authenticationProtocol: deviceCode detection remains the primary signal.
    Prevention via CA policy (error 53003) is the most effective mitigation.

# PENDING LAB VALIDATION
# CA policy status: Confirm whether tenant has "Block device code flow" CA policy.
# If policy is deployed, the research rule will return zero interactive results (expected).
# RawLogs: No sample Entra ID device-code sign-in log entries attached yet.
# Missing Sigma rule for FOCI token exchange stage (NonInteractiveUserSignInLogs).
# filter_known_legitimate/filter_known_automation: Replace <UNKNOWN> placeholders
# in hunt.yml and analyst.yml with tenant-specific known-good MAB sources.
# Field name verification: authenticationProtocol vs AuthenticationProtocol casing.

TheConstant: >
  authenticationProtocol: deviceCode + MAB app ID 29d9ed98-... + resultType 0 +
  isInteractive on Entra ID sign-in event when victim redeems device code