[New Rule] Potential Masquerading as Communication Apps (#2780)

* [New Rule] Potential Masquerading as Communication Apps

* ocd

* Update defense_evasion_masquerading_communication_apps.toml

* Update defense_evasion_masquerading_communication_apps.toml

* Update rules/windows/defense_evasion_masquerading_communication_apps.toml

* Update rules/windows/defense_evasion_masquerading_communication_apps.toml

* Apply suggestions from code review

* Merge branch 'main' into comms_masquerade

* Move to BBR folder

* Revert "Merge branch 'main' into comms_masquerade"

This reverts commit 726c63c0cab782a83d9f505e54e55d4edd1f5589.

rules_building_block/defense_evasion_masquerading_communication_apps.toml

@@ -0,0 +1,88 @@
+[metadata]
+creation_date = "2023/05/05"
+integration = ["endpoint"]
+maturity = "production"
+min_stack_comments = "New fields added: required_fields, related_integrations, setup"
+min_stack_version = "8.3.0"
+updated_date = "2023/06/30"
+bypass_bbr_timing = true
+
+[rule]
+author = ["Elastic"]
+description = """
+Identifies suspicious instances of communications apps, both unsigned and renamed ones, that can indicate an attempt to
+conceal malicious activity, bypass security features such as allowlists, or trick users into executing malware.
+"""
+from = "now-9m"
+index = ["logs-endpoint.events.*"]
+language = "eql"
+license = "Elastic License v2"
+name = "Potential Masquerading as Communication Apps"
+risk_score = 21
+rule_id = "c9482bfa-a553-4226-8ea2-4959bd4f7923"
+severity = "low"
+tags = ["Domain: Endpoint", "OS: Windows", "Use Case: Threat Detection", "Tactic: Defense Evasion"]
+timestamp_override = "event.ingested"
+building_block_type = "default"
+type = "eql"
+
+query = '''
+process where host.os.type == "windows" and
+  event.type == "start" and
+  (
+    /* Slack */
+    (process.name : "slack.exe" and not
+      (process.code_signature.subject_name : "Slack Technologies, Inc." and process.code_signature.trusted == true)
+    ) or
+
+    /* WebEx */
+    (process.name : "WebexHost.exe" and not
+      (process.code_signature.subject_name : ("Cisco WebEx LLC", "Cisco Systems, Inc.") and process.code_signature.trusted == true)
+    ) or
+
+    /* Teams */
+    (process.name : "Teams.exe" and not
+      (process.code_signature.subject_name : "Microsoft Corporation" and process.code_signature.trusted == true)
+    ) or
+
+    /* Discord */
+    (process.name : "Discord.exe" and not
+      (process.code_signature.subject_name : "Discord Inc." and process.code_signature.trusted == true)
+    ) or
+
+    /* RocketChat */
+    (process.name : "Rocket.Chat.exe" and not
+      (process.code_signature.subject_name : "Rocket.Chat Technologies Corp." and process.code_signature.trusted == true)
+    ) or
+
+    /* Mattermost */
+    (process.name : "Mattermost.exe" and not
+      (process.code_signature.subject_name : "Mattermost, Inc." and process.code_signature.trusted == true)
+    ) or
+
+    /* WhatsApp */
+    (process.name : "WhatsApp.exe" and not
+      (process.code_signature.subject_name : "WhatsApp LLC" and process.code_signature.trusted == true)
+    ) or
+
+    /* Zoom */
+    (process.name : "Zoom.exe" and not
+      (process.code_signature.subject_name : "Zoom Video Communications, Inc." and process.code_signature.trusted == true)
+    )
+  )
+'''
+
+
+[[rule.threat]]
+framework = "MITRE ATT&CK"
+[[rule.threat.technique]]
+id = "T1036"
+name = "Masquerading"
+reference = "https://attack.mitre.org/techniques/T1036/"
+
+
+[rule.threat.tactic]
+id = "TA0005"
+name = "Defense Evasion"
+reference = "https://attack.mitre.org/tactics/TA0005/"
+