Connection to Commonly Abused Free SSL Certificate Providers

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: 7

Rule authors:

Elastic

Rule license: Elastic License v2

Investigation guide

edit

## Setup

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&CK^TM

Tactic:
- Name: Command and Control
- ID: TA0011
- Reference URL: https://attack.mitre.org/tactics/TA0011/
Technique:
- Name: Encrypted Channel
- ID: T1573
- Reference URL: https://attack.mitre.org/techniques/T1573/

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