Connection to Commonly Abused Free SSL Certificate Providers

edit

Connection to Commonly Abused Free SSL Certificate Providers

edit

Identifies unusual processes connecting to domains using known free SSL certificates. Adversaries may employ a known encryption algorithm to conceal command and control traffic.

Rule type: eql

Rule indices:

  • winlogbeat-*
  • logs-endpoint.events.*
  • logs-windows.*

Severity: low

Risk score: 21

Runs every: 5m

Searches indices from: now-9m (Date Math format, see also Additional look-back time)

Maximum alerts per execution: 100

References: None

Tags:

  • Elastic
  • Host
  • Windows
  • Threat Detection
  • Command and Control

Version: 4

Rule authors:

  • Elastic

Rule license: Elastic License v2

Investigation guide

edit
## Config

If 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.

Rule query

edit
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")

Framework: MITRE ATT&CKTM