Suspicious Execution via setsid and nohup Sync RTA (#3941)

Co-authored-by: shashank-elastic <91139415+shashank-elastic@users.noreply.github.com>

rta/linux_execution_setsid_nohup_unusual_execution.py

@@ -0,0 +1,40 @@
+# Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+# or more contributor license agreements. Licensed under the Elastic License
+# 2.0; you may not use this file except in compliance with the Elastic License
+# 2.0.
+
+from . import common
+from . import RtaMetadata
+
+metadata = RtaMetadata(
+    uuid="66ff975c-fa48-47c4-965a-8f363425369e",
+    platforms=["linux"],
+    endpoint=[
+        {
+            "rule_name": "Suspicious Execution via setsid and nohup",
+            "rule_id": "18d82674-08d0-408e-801b-468e1b06298f"
+        }
+    ],
+    techniques=["T1059", "T1071"],
+)
+
+
+@common.requires_os(*metadata.platforms)
+def main():
+
+    common.log("Creating a fake nohup executable..")
+    masquerade = "/tmp/nohup"
+    source = common.get_path("bin", "netcon_exec_chain.elf")
+    common.copy_file(source, masquerade)
+    common.log("Granting execute permissions...")
+    common.execute(['chmod', '+x', masquerade])
+
+    commands = [masquerade, 'exec', '-c', '/dev/tcp']
+    common.execute([*commands], timeout=5, kill=True)
+    common.log("Cleaning...")
+    common.remove_file(masquerade)
+    common.log("Simulation successfull!")
+
+
+if __name__ == "__main__":
+    exit(main())