M365 Identity OAuth Illicit Consent Grant by Rare Client and User

  1[metadata]
  2creation_date = "2025/03/24"
  3integration = ["o365"]
  4maturity = "production"
  5updated_date = "2026/07/15"
  6
  7[rule]
  8author = ["Elastic"]
  9description = """
 10Identifies an Microsoft 365 illicit consent grant request on-behalf-of a registered Entra ID application. Adversaries
 11may create and register an application in Microsoft Entra ID for the purpose of requesting user consent to access
 12resources in Microsoft 365. This is accomplished by tricking a user into granting consent to the application, typically
 13via a pre-made phishing URL. This establishes an OAuth grant that allows the malicious client applocation to access
 14resources in Microsoft 365 on-behalf-of the user.
 15"""
 16from = "now-9m"
 17index = ["logs-o365.audit-*"]
 18language = "kuery"
 19license = "Elastic License v2"
 20name = "M365 Identity OAuth Illicit Consent Grant by Rare Client and User"
 21note = """## Triage and analysis
 22
 23### Investigating M365 Identity OAuth Illicit Consent Grant by Rare Client and User
 24
 25Adversaries may register a malicious application in Microsoft Entra ID and trick users into granting excessive permissions via OAuth consent. These apps can access sensitive Microsoft 365 data—such as mail, profiles, and files—on behalf of the user once consent is granted. This activity is often initiated through spearphishing campaigns that direct the user to a pre-crafted OAuth consent URL.
 26
 27This rule identifies a new consent grant to an application using Microsoft 365 audit logs. Additionally, this is a New Terms rule that will only trigger if the user and client ID have not been seen doing this activity in the last 14 days.
 28
 29#### Possible investigation steps
 30
 31- **Review the app in Entra ID**:
 32  - Go to **Enterprise Applications** in the Azure portal.
 33  - Search for the `AppId` or name from `o365.audit.ObjectId`.
 34  - Review granted API permissions and whether admin consent was required.
 35  - Check the `Publisher` and `Verified` status.
 36
 37- **Assess the user who granted consent**:
 38  - Investigate `o365.audit.UserId` (e.g., `terrance.dejesus@...`) for signs of phishing or account compromise.
 39  - Check if the user was targeted in recent phishing simulations or campaigns.
 40  - Review the user’s sign-in logs for suspicious geolocation, IP, or device changes.
 41
 42- **Determine scope and risk**:
 43  - Check `o365.audit.ModifiedProperties.ConsentAction_Reason.NewValue` to determine whether Microsoft's own risk heuristics flagged the application. A value of `Risky application detected` means Microsoft scored the app as suspicious at the time consent was granted and should raise the priority of the review. This reason is only populated on admin-consent events, and its absence does not clear the application; a flagged app is also not necessarily malicious, since Microsoft's heuristic can flag legitimate apps.
 44  - Use the `ConsentContext_IsAdminConsent` and `ConsentContext_OnBehalfOfAll` flags to assess privilege level.
 45  - Review `o365.audit.ModifiedProperties.ConsentAction_Permissions.NewValue` for the granted scopes. Combinations such as `offline_access` with `Mail.ReadWrite`, `Files.ReadWrite.All`, or `Chat.Read` are characteristic of mailbox and file exfiltration and indicate potential data exposure.
 46  - Cross-reference affected `Target` objects with known business-critical assets or data owners.
 47
 48- **Correlate additional telemetry**:
 49  - Review logs from Defender for Cloud Apps (MCAS), Microsoft Purview, or other DLP tooling for unusual access patterns.
 50  - Search for `AppId` across your tenant to determine how widely it's used.
 51
 52### False positive analysis
 53
 54- Not all consent grants are malicious. Verify if the app is business-approved, listed in your app catalog, or commonly used by users in that role or department.
 55- Consent reasons like `WindowsAzureActiveDirectoryIntegratedApp` could relate to integrated services, though these still require verification.
 56- A `ConsentAction_Reason` of `Risky application detected` raises confidence that the consent is worth investigating, but Microsoft's risk heuristic is advisory and can flag legitimate applications (including internal line-of-business apps and newly registered tenant applications). Its absence does not make the consent benign, so weigh it alongside the requested scopes, admin-consent context, and the application's publisher.
 57
 58### Response and remediation
 59
 60- **If the app is confirmed malicious**:
 61  - Revoke OAuth consent using the [Microsoft Graph API](https://learn.microsoft.com/en-us/graph/api/oauth2permissiongrant-delete).
 62  - Remove any related service principals from Entra ID.
 63  - Block the app via the Conditional Access "Grant" control or Defender for Cloud Apps policies.
 64  - Revoke refresh tokens and require reauthentication for affected users.
 65  - Notify end-users and IT of the potential exposure.
 66  - Activate your phishing or OAuth abuse response playbook.
 67
 68- **Prevent future misuse**:
 69  - Enable the [Admin consent workflow](https://learn.microsoft.com/en-us/azure/active-directory/manage-apps/configure-admin-consent-workflow) to restrict user-granted consent.
 70  - Audit and reduce overprivileged applications in your environment.
 71  - Consider using Defender for Cloud Apps OAuth app governance.
 72
 73"""
 74references = [
 75    "https://www.wiz.io/blog/midnight-blizzard-microsoft-breach-analysis-and-best-practices",
 76    "https://docs.microsoft.com/en-us/microsoft-365/security/office-365-security/detect-and-remediate-illicit-consent-grants?view=o365-worldwide",
 77    "https://www.cloud-architekt.net/detection-and-mitigation-consent-grant-attacks-azuread/",
 78    "https://docs.microsoft.com/en-us/defender-cloud-apps/investigate-risky-oauth#how-to-detect-risky-oauth-apps",
 79    "https://learn.microsoft.com/en-us/office/office-365-management-api/office-365-management-activity-api-schema",
 80]
 81risk_score = 47
 82rule_id = "0c3c80de-08c2-11f0-bd11-f661ea17fbcc"
 83severity = "medium"
 84tags = [
 85    "Domain: Cloud",
 86    "Data Source: Microsoft 365",
 87    "Data Source: Microsoft 365 Audit Logs",
 88    "Use Case: Identity and Access Audit",
 89    "Resources: Investigation Guide",
 90    "Tactic: Initial Access",
 91    "Tactic: Credential Access",
 92]
 93timestamp_override = "event.ingested"
 94type = "new_terms"
 95
 96query = '''
 97data_stream.dataset: "o365.audit"
 98  and o365.audit.Actor.Type: 5
 99  and event.action: "Consent to application."
100  and event.outcome: "success"
101  and o365.audit.Target.Type: (0 or 2 or 3 or 9 or 10)
102  and o365.audit.UserId: *
103  and o365.audit.ObjectId: *
104'''
105
106
107[[rule.threat]]
108framework = "MITRE ATT&CK"
109
110[[rule.threat.technique]]
111id = "T1566"
112name = "Phishing"
113reference = "https://attack.mitre.org/techniques/T1566/"
114
115[[rule.threat.technique.subtechnique]]
116id = "T1566.002"
117name = "Spearphishing Link"
118reference = "https://attack.mitre.org/techniques/T1566/002/"
119
120[rule.threat.tactic]
121id = "TA0001"
122name = "Initial Access"
123reference = "https://attack.mitre.org/tactics/TA0001/"
124
125[[rule.threat]]
126framework = "MITRE ATT&CK"
127
128[[rule.threat.technique]]
129id = "T1528"
130name = "Steal Application Access Token"
131reference = "https://attack.mitre.org/techniques/T1528/"
132
133[rule.threat.tactic]
134id = "TA0006"
135name = "Credential Access"
136reference = "https://attack.mitre.org/tactics/TA0006/"
137
138[[rule.threat]]
139framework = "MITRE ATT&CK"
140
141[[rule.threat.technique]]
142id = "T1098"
143name = "Account Manipulation"
144reference = "https://attack.mitre.org/techniques/T1098/"
145
146[rule.threat.tactic]
147id = "TA0003"
148name = "Persistence"
149reference = "https://attack.mitre.org/tactics/TA0003/"
150[rule.investigation_fields]
151field_names = [
152    "@timestamp",
153    "event.action",
154    "event.outcome",
155    "o365.audit.UserId",
156    "o365.audit.ObjectId",
157    "o365.audit.Actor.Type",
158    "o365.audit.Target.Type",
159    "o365.audit.ModifiedProperties.ConsentAction_Reason.NewValue",
160    "o365.audit.ExtendedProperties.additionalDetails",
161    "cloud.region"
162]
163
164[rule.new_terms]
165field = "new_terms_fields"
166value = ["o365.audit.UserId", "o365.audit.ObjectId"]
167[[rule.new_terms.history_window_start]]
168field = "history_window_start"
169value = "now-10d"