Protocol or Port Mismatch

SPLUNK detection rule by Rico Valdez, Splunk · Apache-2.0

The following analytic identifies network traffic where the higher layer protocol does not match the expected port, such as non-HTTP traffic on TCP port 80. It leverages data from network traffic inspection technologies like Bro or Palo Alto Networks firewalls. This activity is significant because it may indicate attempts to bypass firewall restrictions or conceal malicious communications. If confirmed malicious, this behavior could allow attackers to evade detection, maintain persistence, or exfiltrate data through commonly allowed ports, posing a significant threat to network security.

name: Protocol or Port Mismatch
id: 54dc1265-2f74-4b6d-b30d-49eb506a31b3
version: 12
creation_date: '2020-04-29'
modification_date: '2026-05-13'
author: Rico Valdez, Splunk
status: production
type: Anomaly
description: The following analytic identifies network traffic where the higher layer protocol does not match the expected port, such as non-HTTP traffic on TCP port 80. It leverages data from network traffic inspection technologies like Bro or Palo Alto Networks firewalls. This activity is significant because it may indicate attempts to bypass firewall restrictions or conceal malicious communications. If confirmed malicious, this behavior could allow attackers to evade detection, maintain persistence, or exfiltrate data through commonly allowed ports, posing a significant threat to network security.
data_source:
    - Cisco Secure Firewall Threat Defense Connection Event
search: |
    | tstats `security_content_summariesonly`
      count min(_time) as firstTime
            max(_time) as lastTime

    from datamodel=Network_Traffic where

    (
      All_Traffic.app=dns
      NOT All_Traffic.dest_port IN (53)
    )
    OR
    (
      All_Traffic.app IN (web-browsing, http)
      NOT All_Traffic.dest_port IN (80, 8000, 8080)
    )
    OR
    (
      All_Traffic.app=ssl
      NOT All_Traffic.dest_port IN (443, 465, 993, 8443)
    )
    OR
    (
      All_Traffic.app=smtp
      NOT All_Traffic.dest_port IN (25, 587, 2525)
    )

    by All_Traffic.src_ip All_Traffic.dest_ip All_Traffic.app,
       All_Traffic.dest_port All_Traffic.transport
       All_Traffic.action All_Traffic.rule

    |`security_content_ctime(firstTime)`
    | `security_content_ctime(lastTime)`
    | `drop_dm_object_name("All_Traffic")`
    | `protocol_or_port_mismatch_filter`
how_to_implement: Running this search properly requires a technology that can inspect network traffic and identify common protocols. Technologies such as Zeek, Cisco Secure Firewall or Palo Alto Networks firewalls are examples that will identify protocols via inspection, and not just assume a specific protocol based on the transport protocol and ports.
known_false_positives: Some false positive could occur with some applications that change their default communication port for an added layer of obscurity.
references: []
drilldown_searches:
    - name: View the detection results for - "$src_ip$"
      search: '%original_detection_search% | search  src_ip = "$src_ip$"'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
    - name: View risk events for the last 7 days for - "$src_ip$"
      search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$src_ip$") | stats count min(_time) as firstTime max(_time) as lastTime values(search_name) as "Search Name" values(risk_message) as "Risk Message" values(analyticstories) as "Analytic Stories" values(annotations._all) as "Annotations" values(annotations.mitre_attack.mitre_tactic) as "ATT&CK Tactics" by normalized_risk_object | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)`'
      earliest_offset: 7d
      latest_offset: "0"
intermediate_findings:
    entities:
        - field: src_ip
          type: system
          score: 20
          message: Port or Protocol Traffic Mismatch [ $src_ip$ ]
threat_objects:
    - field: dest_ip
      type: ip_address
analytic_story:
    - Prohibited Traffic Allowed or Protocol Mismatch
    - Command And Control
    - Cisco Secure Firewall Threat Defense Analytics
asset_type: Endpoint
mitre_attack_id:
    - T1048.003
product:
    - Splunk Enterprise
    - Splunk Enterprise Security
    - Splunk Cloud
category: network
security_domain: network
tests:
    - name: Cisco Secure Firewall True Positive Test
      attack_data:
        - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/cisco_secure_firewall_threat_defense/connection_event/connection_events.log
          source: not_applicable
          sourcetype: cisco:sfw:estreamer
      test_type: unit

[[ currentRule.title && currentRule.title.length > 60 ? currentRule.title.slice(0, 60) + '…' : currentRule.title ]]

b44ad7e9-7c6e-4455-ac27-e8dc7425287a

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Executable code, not a declarative rule

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Format & documentation suggestions

Not a security issue — this rule is valid and was accepted as-is. These are optional fields/conventions its own format recommends, mainly affecting its quality score and how well it documents itself for other reviewers.

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