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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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: 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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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&CK^TM

Tactic:
- Name: Command and Control
- ID: TA0011
- Reference URL: https://attack.mitre.org/tactics/TA0011/
Tactic:
- Name: Exfiltration
- ID: TA0010
- Reference URL: https://attack.mitre.org/tactics/TA0010/
Technique:
- Name: Exfiltration Over Alternative Protocol
- ID: T1048
- Reference URL: https://attack.mitre.org/techniques/T1048/

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: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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