IMPORTANT: No additional bug fixes or documentation updates will be released for this version. For the latest information, see the current release documentation.

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Telnet Port Activity

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Telnet Port Activity

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This rule detects network events that may indicate the use of Telnet traffic. Telnet is commonly used by system administrators to remotely control older or embed ed systems using the command line shell. It should almost never be directly exposed to the Internet, as it is frequently targeted and exploited by threat actors as an initial access or back-door vector. As a plain-text protocol, it may also expose usernames and passwords to anyone capable of observing the traffic.

Rule type: query

Rule indices:

auditbeat-*
filebeat-*
packetbeat-*
logs-endpoint.events.*

Severity: medium

Risk score: 47

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
Network
Threat Detection
Command and Control
Host

Version: 8 (version history)

Added (Elastic Stack release): 7.6.0

Last modified (Elastic Stack release): 7.14.0

Rule authors: Elastic

Rule license: Elastic License v2

Potential false positives

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IoT (Internet of Things) devices and networks may use telnet and can be excluded if desired. Some business work-flows may use Telnet for administration of older devices. These often have a predictable behavior. Telnet activity involving an unusual source or destination may be more suspicious. Telnet activity involving a production server that has no known associated Telnet work-flow or business requirement is often suspicious.

Rule query

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event.category:(network or network_traffic) and network.transport:tcp
and destination.port:23

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/
Tactic:
- Name: Lateral Movement
- ID: TA0008
- Reference URL: https://attack.mitre.org/tactics/TA0008/
Technique:
- Name: Remote Services
- ID: T1021
- Reference URL: https://attack.mitre.org/techniques/T1021/
Tactic:
- Name: Initial Access
- ID: TA0001
- Reference URL: https://attack.mitre.org/tactics/TA0001/
Technique:
- Name: Exploit Public-Facing Application
- ID: T1190
- Reference URL: https://attack.mitre.org/techniques/T1190/

Rule version history

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Version 8 (7.14.0 release)

Updated query, changed from:

event.category:(network or network_traffic) and network.transport:tcp
and destination.port:23

Version 7 (7.12.0 release)

Formatting only

Version 6 (7.11.2 release)

Formatting only

Version 5 (7.11.0 release)

Formatting only

Version 4 (7.10.0 release)

Formatting only

Version 3 (7.9.0 release)

Updated query, changed from:

network.transport:tcp and destination.port:23

Version 2 (7.6.1 release)

Removed auditbeat-*, packetbeat-*, and winlogbeat-* from the rule indices.

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