[New Rule] External Authentication Method Addition or Modification in Entra ID (#4906)

* new rule External Authentication Method Addition or Modification in Entra ID

* added references

* adjusted to new terms

Author: terrancedejesus

rules/integrations/azure/persistence_graph_eam_addition_or_modification.toml

@@ -0,0 +1,101 @@
+[metadata]
+creation_date = "2025/07/14"
+integration = ["azure"]
+maturity = "production"
+updated_date = "2025/07/14"
+
+[rule]
+author = ["Elastic"]
+description = """
+Identifies when an external authentication method (EAM) is added or modified in Entra ID. EAM may allow adversaries to
+bypass multi-factor authentication (MFA) requirements, potentially leading to unauthorized access to user accounts and
+sensitive resources by using bring-your-own IdP (BYOIDP) methods.
+"""
+from = "now-9m"
+index = ["filebeat-*", "logs-azure.graphactivitylogs-*"]
+language = "kuery"
+license = "Elastic License v2"
+name = "External Authentication Method Addition or Modification in Entra ID"
+note = """## Triage and analysis
+
+### Investigating External Authentication Method Addition or Modification in Entra ID
+
+This rule detects suspicious modifications to external authentication methods (EAMs) in Microsoft Entra ID via Microsoft Graph API. Adversaries may abuse this capability to bypass multi-factor authentication (MFA), enabling persistence or unauthorized access through bring-your-own identity provider (BYOIDP) methods.
+
+### Possible investigation steps
+- Validate that `event.action` is `"Microsoft Graph Activity"` and that `http.request.method` is `"PATCH"`, indicating a configuration change was made.
+- Confirm that `url.path` contains the string `authenticationMethodsPolicy`, which is associated with external authentication settings in Entra ID.
+- Review `user.id` to identify the Azure AD object ID of the user or service principal that initiated the change.
+- Examine `azure.graphactivitylogs.properties.app_id` to determine the application ID that performed the action.
+- Analyze `azure.graphactivitylogs.properties.scopes[]` to assess whether the request used privileged scopes such as `AuthenticationMethod.ReadWrite.All`.
+- Review the geographic origin of the request using `source.geo.*` and the `source.ip` field to identify anomalous locations.
+- Examine `user_agent.original` to determine whether the request was made through a browser or automation (e.g., scripted activity).
+- Correlate `azure.graphactivitylogs.properties.token_issued_at` and `azure.graphactivitylogs.properties.time_generated` to assess whether the change occurred shortly after token issuance.
+- Investigate additional activity by the same `user.id` or `app_id` within a short timeframe (e.g., 30 minutes) to detect related suspicious behavior.
+- Use the `operation_id` or `correlation_id` to pivot across related Graph API or Entra ID activity logs, if available.
+
+### False positive analysis
+- Legitimate administrative activity may trigger this rule, such as configuring FIDO2 or enabling passwordless sign-in methods during onboarding or security upgrades.
+- Some enterprise integrations or federated identity providers may programmatically update EAM settings as part of legitimate operations.
+- Routine security assessments or red team exercises may include changes to authentication policies. Validate with internal teams when in doubt.
+- If appropriate, filter or suppress alerts originating from known trusted service principals or administrative accounts.
+
+### Response and remediation
+- Confirm whether the user or application that made the change was authorized to do so. If not, immediately revoke access and reset credentials as needed.
+- Review the application or automation that triggered the change to ensure it is legitimate. If unauthorized, disable or remove it and rotate secrets or tokens it may have accessed.
+- Audit current external authentication configurations and conditional access policies to ensure no persistent backdoors were introduced.
+- Revoke session tokens associated with the change using Entra ID's portal or Microsoft Graph API, and enforce reauthentication where appropriate.
+- Implement stricter RBAC or conditional access policies to prevent unauthorized EAM changes in the future.
+- Monitor for repeat or similar activity from the same source or identity as part of an ongoing compromise assessment.
+"""
+references = ["https://dirkjanm.io/persisting-with-federated-credentials-entra-apps-managed-identities/"]
+risk_score = 47
+rule_id = "42c97e6e-60c3-11f0-832a-f661ea17fbcd"
+severity = "medium"
+tags = [
+    "Domain: Cloud",
+    "Domain: Identity",
+    "Data Source: Azure",
+    "Data Source: Microsoft Graph",
+    "Data Source: Microsoft Graph Activity Logs",
+    "Use Case: Identity and Access Audit",
+    "Resources: Investigation Guide",
+    "Tactic: Persistence",
+]
+timestamp_override = "event.ingested"
+type = "new_terms"
+
+query = '''
+event.dataset: azure.graphactivitylogs and
+    url.path: *authenticationMethodsPolicy* and
+    http.request.method: "PATCH" and
+    http.response.status_code: 200
+'''
+
+
+[[rule.threat]]
+framework = "MITRE ATT&CK"
+[[rule.threat.technique]]
+id = "T1556"
+name = "Modify Authentication Process"
+reference = "https://attack.mitre.org/techniques/T1556/"
+[[rule.threat.technique.subtechnique]]
+id = "T1556.009"
+name = "Conditional Access Policies"
+reference = "https://attack.mitre.org/techniques/T1556/009/"
+
+
+
+[rule.threat.tactic]
+id = "TA0003"
+name = "Persistence"
+reference = "https://attack.mitre.org/tactics/TA0003/"
+
+[rule.new_terms]
+field = "new_terms_fields"
+value = ["azure.graphactivitylogs.properties.user_principal_object_id"]
+[[rule.new_terms.history_window_start]]
+field = "history_window_start"
+value = "now-7d"
+
+