Individual skill
detecting-modbus-protocol-anomalies
This skill covers detecting anomalies in Modbus/TCP and Modbus RTU communications in industrial control systems. It addresses function code monitoring, register range validation, timing analysis, unauthorized client detection, and deep packet inspection for malformed Modbus frames. The skill leverages Zeek with Modbus protocol analyzers, Suricata IDS with OT rules, and custom Python-based detection using Markov chain models for normal Modbus transaction sequences.
internal/tools/skills/data/ot-ics-security/detecting-modbus-protocol-anomalies/SKILL.md
Source commit d42f381ad34843e71a42658e5c57290c713e85af
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- Matches the observed repository HEAD
- Yes
- Scanner rules are current
- Yes
- Repository scan complete
- No
- Skill scan complete
- No
- Observed behavior
- Instructions only
- Last checked
- Nov 9, 2026
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Repository context
- Repository stars (not skill ratings)
- 1,313
- Repository last updated
- Nov 8, 2026
- License
- Apache-2.0
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- cybersecurity Repository topic
- security Repository topic
- bug-bounty Repository topic
- automation Repository topic
- autonomous-pentesting Repository topic
- ai-agent Repository topic
- ai-security Repository topic
- ethical-hacking Repository topic
- golang Repository topic
- penetration-testing Repository topic
- ot-security Declared skill tag
- ics Declared skill tag
- scada Declared skill tag
- industrial-control Declared skill tag
- iec62443 Declared skill tag
- modbus Declared skill tag
- protocol-anomaly Declared skill tag
- security Derived category
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# Detecting Modbus Protocol Anomalies
## When to Use
- When deploying Modbus-specific intrusion detection in an OT environment
- When building baseline models for deterministic Modbus polling patterns
- When investigating suspicious Modbus traffic flagged by OT monitoring tools
- When implementing function code allowlisting on industrial firewalls
- When detecting unauthorized Modbus write commands that could manipulate process setpoints
**Do not use** for securing Modbus communications end-to-end (Modbus has no native security; see implementing-network-segmentation-for-ot for firewall-based controls), for non-Modbus protocol monitoring (see detecting-anomalies-in-industrial-control-systems for multi-protocol), or for active fuzzing of Modbus implementations (see performing-plc-firmware-security-analysis).
## Detection Gaps & Validation
