[metadata]
creation_date = "2020/11/04"
maturity = "production"
updated_date = "2020/11/04"

[rule]
author = ["Elastic"]
description = """
Identifies unusual processes connecting to domains using known free SSL certificates. Adversaries may employ a known
encryption algorithm to conceal command and control traffic.
"""
from = "now-9m"
index = ["winlogbeat-*", "logs-endpoint.events.*"]
language = "eql"
license = "Elastic License"
name = "Connection to Commonly Abused Free SSL Certificate Providers"
risk_score = 21
rule_id = "e3cf38fa-d5b8-46cc-87f9-4a7513e4281d"
severity = "low"
tags = ["Elastic", "Host", "Windows", "Threat Detection", "Command and Control"]
type = "eql"

query = '''
network where network.protocol == "dns" and
  /* Add new free SSL certificate provider domains here */
  dns.question.name : ("*letsencrypt.org", "*.sslforfree.com", "*.zerossl.com", "*.freessl.org") and
  
  /* Native Windows process paths that are unlikely to have network connections to domains secured using free SSL certificates */
  process.executable : ("C:\\Windows\\System32\\*.exe",
                        "C:\\Windows\\System\\*.exe",
	                  "C:\\Windows\\SysWOW64\\*.exe",
		          "C:\\Windows\\Microsoft.NET\\Framework*\\*.exe",
		          "C:\\Windows\\explorer.exe",
		          "C:\\Windows\\notepad.exe") and
  
  /* Insert noisy false positives here */
  not process.name : ("svchost.exe", "MicrosoftEdge*.exe", "msedge.exe")
'''


[[rule.threat]]
framework = "MITRE ATT&CK"
[[rule.threat.technique]]
id = "T1573"
name = "Encrypted Channel"
reference = "https://attack.mitre.org/techniques/T1573/"


[rule.threat.tactic]
id = "TA0011"
name = "Command and Control"
reference = "https://attack.mitre.org/tactics/TA0011/"
