adding detection

detections/cloud/azure_ad_multiple_denied_mfa_requests_for_user.yml

@@ -0,0 +1,64 @@
+name: Azure AD Multiple Denied MFA Requests For User
+id: d0895c20-de71-4fd2-b56c-3fcdb888eba1
+version: 1
+date: '2023-10-31'
+author: Mauricio Velazco, Splunk
+status: production
+type: TTP
+data_source: []
+description: This analytic targets the detection of an unusually high number of denied Multi-Factor Authentication (MFA) requests for a single user within a 10-minute window, specifically identifying instances where more than nine MFA prompts were declined by the user. Utilizing Azure Active Directory (Azure AD) sign-in logs, particularly focusing on "Sign-in activity" events, it filters for scenarios where the MFA request was denied due to the user declining the authentication, as indicated by error code 500121 and additional details stating "MFA denied; user declined the authentication." The data is then aggregated into 10-minute intervals, counting distinct raw events and capturing the earliest and latest times of occurrence for each user. This behavior is significant for a Security Operations Center (SOC) as it could be an early indicator of a targeted attack or an account compromise attempt, with an attacker having obtained the user's credentials and the user actively declining the MFA prompts, preventing unauthorized access. A true positive detection would imply that an attacker is on the verge of gaining full access to the user's account, posing a threat that could lead to data exfiltration, lateral movement, or further malicious activities within the organization, necessitating immediate investigation and response to safeguard the organization's assets.
+search: '`azure_monitor_aad` category=SignInLogs category="Sign-in activity"
+  | rename properties.* as * 
+  | search status.errorCode=500121 status.additionalDetails="MFA denied; user declined the authentication"
+  | bucket span=10m _time 
+  | stats dc(_raw) AS mfa_prompts earliest(_time) as firstTime latest(_time) as lastTime by user, status.additionalDetails, appDisplayName, userAgent, _time 
+  | where mfa_prompts > 9
+  | `security_content_ctime(firstTime)`
+  | `security_content_ctime(lastTime)`
+  | `azure_ad_multiple_denied_mfa_requests_for_user_filter`'
+how_to_implement: You must install the latest version of Splunk Add-on for Microsoft
+  Cloud Services from Splunkbase (https://splunkbase.splunk.com/app/3110/#/details). You must be ingesting Azure Active Directory events into your Splunk environment through an EventHub.
+  This analytic was written to be used with the azure:monitor:aad sourcetype leveraging the Signin log category.
+known_false_positives: UPDATE_KNOWN_FALSE_POSITIVES
+references:
+- https://www.mandiant.com/resources/blog/russian-targeting-gov-business
+- https://arstechnica.com/information-technology/2022/03/lapsus-and-solar-winds-hackers-both-use-the-same-old-trick-to-bypass-mfa/
+- https://therecord.media/russian-hackers-bypass-2fa-by-annoying-victims-with-repeated-push-notifications/
+- https://attack.mitre.org/techniques/T1621/
+- https://attack.mitre.org/techniques/T1078/004/
+tags:
+  analytic_story:
+  - Azure Active Directory Account Takeover
+  asset_type: Azure Active Directory
+  confidence: 90
+  impact: 60
+  atomic_guid: []
+  message: User $user$ denied more than 9 MFA requests in a timespan of 10 minutes.
+  mitre_attack_id:
+  - T1621
+  observable:
+  - name: user
+    type: User
+    role:
+    - Victim
+  product:
+  - Splunk Enterprise
+  - Splunk Enterprise Security
+  - Splunk Cloud
+  risk_score: 54
+  required_fields:
+  - _time
+  - category
+  - category
+  - properties.status.errorCode
+  - properties.status.additionalDetails
+  - user
+  - properties.appDisplayName
+  - properties.userAgent
+  security_domain: identity
+tests:
+- name: True Positive Test
+  attack_data:
+  - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1621/azure_ad_multiple_denied_mfa_requests/azure_ad_multiple_denied_mfa_requests.log
+    source: Azure AD
+    sourcetype: azure:monitor:aad