[New Rule] Hosts File Modified (#25)

rta/hosts_file_modify.py

@@ -0,0 +1,54 @@
+# Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+# or more contributor license agreements. Licensed under the Elastic License;
+# you may not use this file except in compliance with the Elastic License.
+
+# Name: Hosts File Modified
+# RTA: hosts_file_modify.py
+# ATT&CK: T1492
+# Description: Modifies the hosts file
+
+import os
+import random
+import time
+
+from string import ascii_letters
+
+from . import common
+
+
+def main():
+    hosts_files = {
+        common.WINDOWS: "C:\\Windows\\system32\\drivers\\etc\\hosts",
+        common.LINUX: "/etc/hosts",
+        common.MACOS: "/private/etc/hosts"
+    }
+    hosts_file = hosts_files[common.CURRENT_OS]
+
+    backup = os.path.abspath(hosts_file + '_backup')
+    common.log("Backing up original 'hosts' file.")
+    common.copy_file(hosts_file, backup)
+
+    # add randomness for diffs for FIM module
+    randomness = ''.join(random.sample(ascii_letters, 10))
+    entry = [
+        '',
+        '# RTA hosts_modify was here',
+        '# 8.8.8.8 https://www.{random}.google.com'.format(random=randomness)
+    ]
+    with open(hosts_file, 'a') as f:
+        f.write('\n'.join(entry))
+
+    common.log('Updated hosts file')
+    with open(hosts_file, 'r') as f:
+        common.log(f.read())
+
+    time.sleep(2)
+
+    # cleanup
+    common.log("Restoring hosts from backup copy.")
+    common.copy_file(backup, hosts_file)
+    os.remove(backup)
+
+
+if __name__ == "__main__":
+    exit(main())

rules/cross-platform/impact_hosts_file_modified.toml

@@ -0,0 +1,43 @@
+[metadata]
+creation_date = "2020/07/07"
+ecs_version = ["1.6.0"]
+maturity = "production"
+updated_date = "2020/07/07"
+
+[rule]
+author = ["Elastic"]
+description = """
+The hosts file on endpoints is used to control manual IP address to hostname resolutions. The hosts file is the first
+point of lookup for DNS hostname resolution so if adversaries can modify the endpoint hosts file, they can route traffic
+to malicious infrastructure. This rule detects modifications to the hosts file on Microsoft Windows, Linux (Ubuntu or
+RHEL) and macOS systems.
+"""
+index = ["auditbeat-*", "winlogbeat-*", "logs-endpoint.events.*"]
+language = "kuery"
+license = "Elastic License"
+name = "Hosts File Modified"
+note = "For Windows systems using Auditbeat, this rule requires adding 'C:/Windows/System32/drivers/etc' as an additional path in the 'file_integrity' module of auditbeat.yml."
+references = ["https://www.elastic.co/guide/en/beats/auditbeat/current/auditbeat-reference-yml.html"]
+risk_score = 47
+rule_id = "9c260313-c811-4ec8-ab89-8f6530e0246c"
+severity = "medium"
+tags = ["Elastic", "Linux", "Windows", "macOS"]
+type = "query"
+
+query = '''
+event.category:file and event.type:(change or creation) and file.path:("/private/etc/hosts" or "/etc/hosts" or "C:\Windows\System32\drivers\etc\hosts")
+'''
+
+
+[[rule.threat]]
+framework = "MITRE ATT&CK"
+[[rule.threat.technique]]
+id = "T1492"
+name = "Stored Data Manipulation"
+reference = "https://attack.mitre.org/techniques/T1492/"
+
+
+[rule.threat.tactic]
+id = "TA0040"
+name = "Impact"
+reference = "https://attack.mitre.org/tactics/TA0040/"