SSH (Secure Shell) to the Internet

Detects network events that may indicate the use of SSH traffic to the Internet. SSH is commonly used by system administrators to remotely control a system using the command line shell. If it is exposed to the Internet, it should be done with strong security controls as it is frequently targeted and exploited by threat actors as an initial access or back-door vector.

Rule indices:

filebeat-*

Severity: low

Risk score: 21

Runs every: 5 minutes

Searches indices from: now-6m (Date Math format, see also Additional look-back time)

Maximum signals per execution: 100

Tags:

Elastic
Network

Rule version: 2 (version history)

Added (Elastic Stack release): 7.6.0

Last modified (Elastic Stack release): 7.6.1

Potential false positives

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SSH connections may be made directly to Internet destinations in order to access Linux cloud server instances but such connections are usually made only by engineers. In such cases, only SSH gateways, bastions or jump servers may be expected Internet destinations and can be exempted from this rule. SSH may be required by some workflows such as remote access and support for specialized software products and servers. Such workflows are usually known and not unexpected. Usage that is unfamiliar to server or network owners can be unexpected and suspicious.

Rule query

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network.transport: tcp and destination.port:22 and (
network.direction: outbound or ( source.ip: (10.0.0.0/8 or
172.16.0.0/12 or 192.168.0.0/16) and not destination.ip:
(10.0.0.0/8 or 172.16.0.0/12 or 192.168.0.0/16) ) )

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: Commonly Used Port
- ID: T1043
- Reference URL: https://attack.mitre.org/techniques/T1043/

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