Out of the Gates

Microsoft Exchange Mailbox Replication service writing Active Server Pages

detections/experimental/endpoint/microsoft_exchange_mailbox_replication_service_writing_active_server_pages.yml

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+name: Microsoft Exchange Mailbox Replication service writing Active Server Pages
+id: 985f322c-57a5-11ec-b9ac-acde48001122
+version: 1
+date: '2021-12-07'
+author: Michael Haag, Splunk
+type: TTP
+datamodel:
+- Endpoint
+description: 'The following query identifies suspicious .aspx created in 3 paths identified
+  by Microsoft as known drop locations for Exchange exploitation related to HAFNIUM
+  group and recently disclosed vulnerablity named ProxyShell. Paths include: `\HttpProxy\owa\auth\`,
+  `\inetpub\wwwroot\aspnet_client\`, and `\HttpProxy\OAB\`. The analytic is limited to process name MSExchangeMailboxReplication.exe, which typically does not write .aspx files to disk.
+  Upon triage, the suspicious
+  .aspx file will likely look obvious on the surface. inspect the contents for script
+  code inside. Identify additional log sources, IIS included, to review source and
+  other potential exploitation. It is often the case that a particular threat is only
+  applicable to a specific subset of systems in your environment. Typically analytics
+  to detect those threats are written without the benefit of being able to only target
+  those systems as well. Writing analytics against all systems when those behaviors
+  are limited to identifiable subsets of those systems is suboptimal. Consider the
+  case ProxyShell vulnerability on Microsoft Exchange Servers. With asset information,
+  a hunter can limit their analytics to systems that have been identified as Exchange
+  servers. A hunter may start with the theory that the exchange server is communicating
+  with new systems that it has not previously. If this theory is run against all publicly
+  facing systems, the amount of noise it will generate will likely render this theory
+  untenable. However, using the asset information to limit this analytic to just the
+  Exchange servers will reduce the noise allowing the hunter to focus only on the
+  systems where this behavioral change is relevant.'
+search: '| tstats `security_content_summariesonly` count FROM datamodel=Endpoint.Processes
+  where Processes.process_name=MSExchangeMailboxReplication.exe  by _time span=1h Processes.process_id Processes.process_name Processes.process_guid
+  Processes.dest | `drop_dm_object_name(Processes)` | join process_guid, _time [|
+  tstats `security_content_summariesonly` count min(_time) as firstTime max(_time)
+  as lastTime FROM datamodel=Endpoint.Filesystem where Filesystem.file_path IN ("*\\HttpProxy\\owa\\auth\\*",
+  "*\\inetpub\\wwwroot\\aspnet_client\\*", "*\\HttpProxy\\OAB\\*") Filesystem.file_name="*.aspx"
+  by _time span=1h Filesystem.dest Filesystem.file_create_time Filesystem.file_name
+  Filesystem.file_path | `drop_dm_object_name(Filesystem)` | fields _time dest file_create_time
+  file_name file_path process_name process_path process process_guid] | dedup file_create_time
+  | table dest file_create_time, file_name, file_path, process_name | `microsoft_exchange_mailbox_replication_service_writing_active_server_pages_filter`'
+how_to_implement: To successfully implement this search you need to be ingesting information
+  on process that include the name of the process responsible for the changes from
+  your endpoints into the `Endpoint` datamodel in the `Processes` node and `Filesystem`
+  node.
+known_false_positives: The query is structured in a way that `action` (read, create)
+  is not defined. Review the results of this query, filter, and tune as necessary.
+  It may be necessary to generate this query specific to your endpoint product.
+references:
+  - https://redcanary.com/blog/blackbyte-ransomware/
+tags:
+  analytic_story:
+  - ProxyShell
+  - Ransomware
+  confidence: 90
+  context:
+  - Source:Endpoint
+  - Stage:Exploitation
+  dataset:
+  - https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1505.003/windows-sysmon_proxylogon.log
+  impact: 90
+  kill_chain_phases:
+  - Exploitation
+  message: A file - $file_name$ was written to disk that is related to IIS exploitation
+    related to ProxyShell. Review further file modifications on endpoint
+    $dest$ by user $user$.
+  mitre_attack_id:
+  - T1505
+  - T1505.003
+  - T1190
+  observable:
+  - name: user
+    type: User
+    role:
+    - Victim
+  - name: dest
+    type: Hostname
+    role:
+    - Victim
+  - name: file_name
+    type: File Name
+    role:
+    - Victim
+  product:
+  - Splunk Enterprise
+  - Splunk Enterprise Security
+  - Splunk Cloud
+  required_fields:
+  - _time
+  - Filesystem.file_path
+  - Filesystem.process_id
+  - Filesystem.file_name
+  - Filesystem.file_hash
+  - Filesystem.user
+  - Filesystem.process_guid
+  - Processes.process_name
+  - Processes.process_id 
+  - Processes.process_name 
+  - Processes.process_guid
+  risk_score: 81
+  security_domain: endpoint
+
+