Connection to Commonly Abused Free SSL Certificate Providers

 1[metadata]
 2creation_date = "2020/11/04"
 3integration = ["endpoint", "windows"]
 4maturity = "production"
 5min_stack_comments = "New fields added: required_fields, related_integrations, setup"
 6min_stack_version = "8.3.0"
 7updated_date = "2023/02/22"
 8
 9[rule]
10author = ["Elastic"]
11description = """
12Identifies unusual processes connecting to domains using known free SSL certificates. Adversaries may employ a known
13encryption algorithm to conceal command and control traffic.
14"""
15from = "now-9m"
16index = ["winlogbeat-*", "logs-endpoint.events.*", "logs-windows.*"]
17language = "eql"
18license = "Elastic License v2"
19name = "Connection to Commonly Abused Free SSL Certificate Providers"
20note = """## Setup
21
22If enabling an EQL rule on a non-elastic-agent index (such as beats) for versions <8.2, events will not define `event.ingested` and default fallback for EQL rules was not added until 8.2, so you will need to add a custom pipeline to populate `event.ingested` to @timestamp for this rule to work.
23"""
24risk_score = 21
25rule_id = "e3cf38fa-d5b8-46cc-87f9-4a7513e4281d"
26severity = "low"
27tags = ["Elastic", "Host", "Windows", "Threat Detection", "Command and Control"]
28timestamp_override = "event.ingested"
29type = "eql"
30
31query = '''
32network where host.os.type == "windows" and network.protocol == "dns" and
33  /* Add new free SSL certificate provider domains here */
34  dns.question.name : ("*letsencrypt.org", "*.sslforfree.com", "*.zerossl.com", "*.freessl.org") and
35
36  /* Native Windows process paths that are unlikely to have network connections to domains secured using free SSL certificates */
37  process.executable : ("C:\\Windows\\System32\\*.exe",
38                        "C:\\Windows\\System\\*.exe",
39	                  "C:\\Windows\\SysWOW64\\*.exe",
40		          "C:\\Windows\\Microsoft.NET\\Framework*\\*.exe",
41		          "C:\\Windows\\explorer.exe",
42		          "C:\\Windows\\notepad.exe") and
43
44  /* Insert noisy false positives here */
45  not process.name : ("svchost.exe", "MicrosoftEdge*.exe", "msedge.exe")
46'''
47
48
49[[rule.threat]]
50framework = "MITRE ATT&CK"
51[[rule.threat.technique]]
52id = "T1573"
53name = "Encrypted Channel"
54reference = "https://attack.mitre.org/techniques/T1573/"
55
56
57[rule.threat.tactic]
58id = "TA0011"
59name = "Command and Control"
60reference = "https://attack.mitre.org/tactics/TA0011/"