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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Connection to Internal Network via Telnet

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Connection to Internal Network via Telnet

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Telnet provides a command line interface for communication with a remote device or server. This rule identifies Telnet network connections to non-publicly routable IP addresses.

Rule type: eql

Rule indices:

auditbeat-*
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

References:

https://www.iana.org/assignments/iana-ipv4-special-registry/iana-ipv4-special-registry.xhtml

Tags:

Elastic
Host
Linux
Threat Detection
Lateral Movement

Version: 7 (version history)

Added (Elastic Stack release): 7.8.0

Last modified (Elastic Stack release): 8.4.0

Rule authors: Elastic

Rule license: Elastic License v2

Potential false positives

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Telnet can be used for both benign or malicious purposes. Telnet is included by default in some Linux distributions, so its presence is not inherently suspicious. The use of Telnet to manage devices remotely has declined in recent years in favor of more secure protocols such as SSH. Telnet usage by non-automated tools or frameworks may be suspicious.

Rule query

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sequence by process.entity_id [process where process.name ==
"telnet" and event.type == "start"] [network where process.name ==
"telnet" and cidrmatch(destination.ip, "10.0.0.0/8",
"127.0.0.0/8", "169.254.0.0/16", "172.16.0.0/12", "192.0.0.0/24",
"192.0.0.0/29", "192.0.0.8/32", "192.0.0.9/32", "192.0.0.10/32",
"192.0.0.170/32", "192.0.0.171/32",
"192.0.2.0/24", "192.31.196.0/24", "192.52.193.0/24",
"192.168.0.0/16", "192.88.99.0/24", "224.0.0.0/4", "100.64.0.0/10",
"192.175.48.0/24", "198.18.0.0/15",
"198.51.100.0/24", "203.0.113.0/24", "240.0.0.0/4", "::1",
"FE80::/10", "FF00::/8")]

Threat mapping

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Framework: MITRE ATT&CK^TM

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/

Rule version history

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Version 7 (8.4.0 release)

Formatting only

Version 6 (7.14.0 release)

Updated query, changed from:

sequence by process.entity_id [process where process.name ==
"telnet" and event.type == "start"] [network where process.name ==
"telnet" and cidrmatch(destination.ip, "10.0.0.0/8",
"172.16.0.0/12", "192.168.0.0/16", "FE80::/10") and not
cidrmatch(destination.ip, "127.0.0.0/8", "::1/128")]

Version 5 (7.12.0 release)

Formatting only

Version 4 (7.10.0 release)

Updated query, changed from:

event.category:network and event.type:(connection or start) and
process.name:telnet and destination.ip:((10.0.0.0/8 or 172.16.0.0/12
or 192.168.0.0/16 or "FE80::/10") and not (127.0.0.0/8 or "::1/128"))

Version 3 (7.9.1 release)

Formatting only

Version 2 (7.9.0 release)

Updated query, changed from:

event.action:("connected-to" or "network_flow") and
process.name:telnet and destination.ip:((10.0.0.0/8 or 172.16.0.0/12
or 192.168.0.0/16 or "FE80::/10") and not (127.0.0.0/8 or "::1/128"))

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