Connection to Commonly Abused Free SSL Certificate Providers

 1[metadata]
 2creation_date = "2020/11/04"
 3integration = ["endpoint", "windows"]
 4maturity = "production"
 5updated_date = "2024/10/15"
 6min_stack_version = "8.14.0"
 7min_stack_comments = "Breaking change at 8.14.0 for the Windows Integration."
 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.network-*", "logs-windows.sysmon_operational-*"]
17language = "eql"
18license = "Elastic License v2"
19name = "Connection to Commonly Abused Free SSL Certificate Providers"
20risk_score = 21
21rule_id = "e3cf38fa-d5b8-46cc-87f9-4a7513e4281d"
22setup = """## Setup
23
24If enabling an EQL rule on a non-elastic-agent index (such as beats) for versions <8.2,
25events will not define `event.ingested` and default fallback for EQL rules was not added until version 8.2.
26Hence for this rule to work effectively, users will need to add a custom ingest pipeline to populate
27`event.ingested` to @timestamp.
28For more details on adding a custom ingest pipeline refer - https://www.elastic.co/guide/en/fleet/current/data-streams-pipeline-tutorial.html
29"""
30severity = "low"
31tags = [
32    "Domain: Endpoint",
33    "OS: Windows",
34    "Use Case: Threat Detection",
35    "Tactic: Command and Control",
36    "Data Source: Elastic Defend",
37    "Data Source: Sysmon",
38]
39timestamp_override = "event.ingested"
40type = "eql"
41
42query = '''
43network where host.os.type == "windows" and network.protocol == "dns" and
44  /* Add new free SSL certificate provider domains here */
45  dns.question.name : ("*letsencrypt.org", "*.sslforfree.com", "*.zerossl.com", "*.freessl.org") and
46
47  /* Native Windows process paths that are unlikely to have network connections to domains secured using free SSL certificates */
48  process.executable : ("C:\\Windows\\System32\\*.exe",
49                        "C:\\Windows\\System\\*.exe",
50	                  "C:\\Windows\\SysWOW64\\*.exe",
51		          "C:\\Windows\\Microsoft.NET\\Framework*\\*.exe",
52		          "C:\\Windows\\explorer.exe",
53		          "C:\\Windows\\notepad.exe") and
54
55  /* Insert noisy false positives here */
56  not process.name : ("svchost.exe", "MicrosoftEdge*.exe", "msedge.exe")
57'''
58
59
60[[rule.threat]]
61framework = "MITRE ATT&CK"
62[[rule.threat.technique]]
63id = "T1573"
64name = "Encrypted Channel"
65reference = "https://attack.mitre.org/techniques/T1573/"
66
67
68[rule.threat.tactic]
69id = "TA0011"
70name = "Command and Control"
71reference = "https://attack.mitre.org/tactics/TA0011/"