Detect Port Security Violation

SPLUNK detection rule by Mikael Bjerkeland, Splunk · Apache-2.0

The following analytic detects port security violations on Cisco switches. It leverages logs from Cisco network devices, specifically looking for events with mnemonics indicating port security violations. This activity is significant because it indicates an unauthorized device attempting to connect to a secured port, potentially bypassing network access controls. If confirmed malicious, this could allow an attacker to gain unauthorized access to the network, leading to data exfiltration, network disruption, or further lateral movement within the environment.

name: Detect Port Security Violation
id: 2de3d5b8-a4fa-45c5-8540-6d071c194d24
version: 11
creation_date: '2020-10-28'
modification_date: '2026-05-13'
author: Mikael Bjerkeland, Splunk
status: experimental
type: TTP
description: The following analytic detects port security violations on Cisco switches. It leverages logs from Cisco network devices, specifically looking for events with mnemonics indicating port security violations. This activity is significant because it indicates an unauthorized device attempting to connect to a secured port, potentially bypassing network access controls. If confirmed malicious, this could allow an attacker to gain unauthorized access to the network, leading to data exfiltration, network disruption, or further lateral movement within the environment.
data_source:
    - Cisco IOS Logs
search: |-
    `cisco_networks` (facility="PM" mnemonic="ERR_DISABLE" disable_cause="psecure-violation") OR (facility="PORT_SECURITY" mnemonic="PSECURE_VIOLATION" OR mnemonic="PSECURE_VIOLATION_VLAN")
      | eval src_interface=src_int_prefix_long+src_int_suffix
      | stats min(_time) AS firstTime max(_time) AS lastTime values(disable_cause) AS disable_cause values(src_mac) AS src_mac values(src_vlan) AS src_vlan values(action) AS action count
        BY host src_interface
      | `security_content_ctime(firstTime)`
      | `security_content_ctime(lastTime)`
      | `detect_port_security_violation_filter`
how_to_implement: This search uses a standard SPL query on logs from Cisco Network devices. The network devices must be configured with Port Security and Error Disable for this to work (see https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst4500/12-2/25ew/configuration/guide/conf/port_sec.html) and log with a severity level of minimum "5 - notification". The search also requires that the Cisco Networks Add-on for Splunk (https://splunkbase.splunk.com/app/1467) is used to parse the logs from the Cisco network devices.
known_false_positives: This search might be prone to high false positives if you have malfunctioning devices connected to your ethernet ports or if end users periodically connect physical devices to the network.
references: []
finding:
    title: Port Securtiy Violation on $host$
    entity:
        field: host
        type: system
        score: 50
analytic_story:
    - Router and Infrastructure Security
asset_type: Infrastructure
mitre_attack_id:
    - T1200
    - T1498
    - T1557.002
product:
    - Splunk Enterprise
    - Splunk Enterprise Security
    - Splunk Cloud
category: network
security_domain: network

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Executable code, not a declarative rule

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