[New Rule] Suspicious RDP ActiveX Client Loaded (#588)

* [New Rule] Suspicious RDP ActiveX Client Loaded

* added exec from mounted device and UNC

* removed unecessary exclusion

* Update rules/windows/lateral_movement_suspicious_rdp_client_imageload.toml

Co-authored-by: dstepanic17 <57736958+dstepanic17@users.noreply.github.com>

Co-authored-by: dstepanic17 <57736958+dstepanic17@users.noreply.github.com>

rules/windows/lateral_movement_suspicious_rdp_client_imageload.toml

@@ -0,0 +1,52 @@
+[metadata]
+creation_date = "2020/11/19"
+ecs_version = ["1.6.0"]
+maturity = "production"
+updated_date = "2020/11/19"
+
+[rule]
+author = ["Elastic"]
+description = """
+Identifies suspicious Image Loading of the Remote Desktop Services ActiveX Client (mstscax), this may indicate the presence
+of RDP lateral movement capability.
+"""
+from = "now-9m"
+index = ["logs-endpoint.events.*", "winlogbeat-*"]
+language = "eql"
+license = "Elastic License"
+name = "Suspicious RDP ActiveX Client Loaded"
+references = ["https://posts.specterops.io/revisiting-remote-desktop-lateral-movement-8fb905cb46c3"]
+risk_score = 47
+rule_id = "71c5cb27-eca5-4151-bb47-64bc3f883270"
+severity = "medium"
+tags = ["Elastic", "Host", "Windows", "Threat Detection", "Lateral Movement"]
+type = "eql"
+
+query = '''
+library where file.name == "mstscax.dll" and
+   /* depending on noise in your env add here extra paths  */
+   wildcard(process.executable, "C:\\Windows\\*",
+                                "C:\\Users\\Public\\*",
+                                "C:\\Users\\Default\\*",
+                                "C:\\Intel\\*",
+                                "C:\\PerfLogs\\*",
+                                "C:\\ProgramData\\*",
+                                "\\Device\\Mup\\*",
+                                "\\\\*") and
+    /* add here FPs */
+   not process.executable in ("C:\\Windows\\System32\\mstsc.exe", "C:\\Windows\\SysWOW64\\mstsc.exe")
+'''
+
+
+[[rule.threat]]
+framework = "MITRE ATT&CK"
+[[rule.threat.technique]]
+id = "T1021"
+name = "Remote Services"
+reference = "https://attack.mitre.org/techniques/T1021/"
+
+
+[rule.threat.tactic]
+id = "TA0008"
+name = "Lateral Movement"
+reference = "https://attack.mitre.org/tactics/TA0008/"