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« Connection to Commonly Abused Web Services Connection to Internal Network via Telnet »
Elastic Docs ›Elastic Security Solution [8.5] ›Detections and alerts ›Prebuilt rule reference

Connection to External Network via Telnet

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Connection to External 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 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:

Tags:

  • Elastic
  • Host
  • Linux
  • Threat Detection
  • Lateral Movement

Version: 100 (version history)

Added (Elastic Stack release): 7.8.0

Last modified (Elastic Stack release): 8.5.0

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 not 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&CKTM

Rule version history

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Version 100 (8.5.0 release)
  • Formatting only
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 not cidrmatch(destination.ip, "127.0.0.0/8",
"10.0.0.0/8", "172.16.0.0/12",
"192.168.0.0/16", "FE80::/10", "::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 not destination.ip:(127.0.0.0/8 or 10.0.0.0/8
or 172.16.0.0/12 or 192.168.0.0/16 or "FE80::/10" 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 not destination.ip:(127.0.0.0/8 or 10.0.0.0/8
or 172.16.0.0/12 or 192.168.0.0/16 or "FE80::/10" or "::1/128")
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