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Elastic Docs ›Elastic Security Solution [master] ›Detections and alerts ›Prebuilt rule reference

SMTP on Port 26/TCP

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SMTP on Port 26/TCP

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This rule detects events that may indicate use of SMTP on TCP port 26. This port is commonly used by several popular mail transfer agents to deconflict with the default SMTP port 25. This port has also been used by a malware family called BadPatch for command and control of Windows systems.

Rule type: query

Rule indices:

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

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

References:

Tags:

  • Elastic
  • Host
  • Network
  • Threat Detection
  • Command and Control
  • Host

Version: 100 (version history)

Added (Elastic Stack release): 7.6.0

Last modified (Elastic Stack release): 8.5.0

Rule authors: Elastic

Rule license: Elastic License v2

Potential false positives

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Servers that process email traffic may cause false positives and should be excluded from this rule as this is expected behavior.

Rule query

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event.category:(network or network_traffic) and network.transport:tcp
and (destination.port:26 or (event.dataset:zeek.smtp and
destination.port:26))

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 9 (8.4.0 release)
  • Formatting only
Version 8 (7.14.0 release)

  • Updated query, changed from:

    event.category:(network or network_traffic) and network.transport:tcp
and (destination.port:26 or (event.dataset:zeek.smtp and
destination.port:26))
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:26
Version 2 (7.6.1 release)
  • Removed auditbeat-*, packetbeat-*, and winlogbeat-* from the rule indices.
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