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Connection to Commonly Abused Free SSL Certificate Providers

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Connection to Commonly Abused Free SSL Certificate Providers

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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: 5 minutes

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

Maximum alerts per execution: 100

Tags:

Elastic
Host
Windows
Threat Detection
Command and Control

Version: 100 (version history)

Added (Elastic Stack release): 7.11.0

Last modified (Elastic Stack release): 8.5.0

Rule authors: Elastic

Rule license: Elastic License v2

Investigation guide

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Rule query

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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")

Threat mapping

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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/

Rule version history

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Version 100 (8.5.0 release)

Formatting only

Version 6 (8.4.0 release)

Updated query, changed from:

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")

Version 4 (8.2.0 release)

Formatting only

Version 3 (7.12.0 release)

Formatting only

Version 2 (7.11.2 release)

Formatting only

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