Hunt: ICS / SCADA / OT

Assumes hunt-core for the scope gate, two-account rule, confirmation gate, enumeration limits, stop conditions, wiki protocol, FIND output, and Deadends. Do not re-derive any of that here.

SAFETY - hard stop, overrides everything below

Writing to a live PLC moves real machinery: it can over-pressure a vessel, over-speed a motor, or disable a safety interlock, and so damage equipment or injure and kill people. Only ever drive a process toward a dangerous state on a target that is EXPLICITLY an authorized lab or CTF simulation. Never on a real plant, and never when scope carries no_dos/passive_only - there OT is READ-ONLY (FC1-4), never write (FC5/6/15/16). The instant the objective is met (e.g. the flag the HMI/CCTV reveals is in hand), STOP writing and revert any coil/register you changed if you can. This is a hard stop and it outranks every other note in this file.

Wiki

qmd_query "ICS SCADA OT Modbus S7comm EtherNet/IP DNP3 OpenPLC Node-RED PLC HMI coil holding register" via wiki-search MCP

Hub: [[network-moc]] (live index). Primary page: [[ics-scada-modbus]]. Payload arsenal: wiki/payloads/modbus.md. Anchors: [[iot-attacks]], [[firmware-hardware]].

Attack surface (ranked by exploitation value)

1. Modbus / TCP 502 - no auth, no session, trivially readable AND writable. The primary lever: FC1-4 read coils/registers, FC5/6/15/16 write them. Highest value, highest danger.
2. OpenPLC web (8080) and Node-RED (1880, dashboard /ui) - the SCADA/IT side that drives the PLC. OpenPLC routes /programs /monitoring /hardware /users; authed OpenPLC = upload-program RCE. Node-RED /ui socket.io config NAMES the registers.
3. HMI web app (Flask/Werkzeug with an /api/... live-state endpoint) - not itself the lever but the ORACLE that tells you whether a write landed.
4. S7comm / TCP 102 (S7/iso-tsap) - python-snap7 db_read for creds/flags in data blocks.
5. EtherNet/IP 44818, DNP3 20000, then BACnet 47808/udp, Fox 1911/4911, OPC-UA 4840 - enumerate with the matching nmap scripts; less commonly the CTF lever, but map them.

Methodology

1. Recon: nmap -p- ... then nmap -Pn -p102,502,20000,44818 --script s7-info,modbus-discover,enip-info,dnp3-info $T. Note the unit/slave id ("sid 0x1").
2. Find the oracle: the HMI /api/state-style endpoint (it reads the PLC and tells you live status). Node-RED /ui socket.io config NAMES the registers ("Read Pressure" = FC3 reg0). This is how you know a write landed.
3. Enumerate Modbus (raw socket, not pymodbus): dump FC1-4, ASCII-decode registers (creds/flags hide there), scan unit ids. Reads (FC1-4) are safe; this step never writes. See [[modbus]].
4. Map process variables -> registers/coils. The pressure/temp/level sensor is a holding/input register; pumps/valves/cooling/safety are coils.
5. Drive to the danger state (authorized lab/CTF ONLY - see SAFETY): FC6 over-drive the process variable to max (65535); then defeat the safety/protection interlock - a controller loop (cooling/relief/ESD) fights you, and it is usually ONE coil. Find it with a BOUNDED, one-write-at-a-time probe, NEVER a free-running write loop (hunt-core: never enumerate writes; this narrow, reverting, oracle-gated probe on an authorized simulation is the sole carve-out): write ONE coil (FC5), read the HMI oracle, and if the state did not flip toward the goal, write that coil back before trying the next. Cover coils 0-31 this way - the control coil is rarely at 0-5, so go wide but stay bounded. If nothing in 0-31 flips the interlock, that is a Deadend; do not widen indefinitely.
6. Read the payoff: HMI flips (e.g. "Explosion Detected!") and points the CCTV/HMI at new media. The flag is frequently a VISUAL overlay in that image/video - fetch it, ffmpeg -i x.mp4 -vf fps=1 f_%02d.jpg, and VIEW the frames (not strings/exif). Objective met -> stop writing (SAFETY).
7. S7: python-snap7 db_read the data blocks (creds/flags). Banner-only sims (s7-info works but no DBs) = decoy.
8. OpenPLC: try openplc:openplc; if changed, do NOT grind the login - the protection is usually disabled directly over Modbus (a coil flag the ladder reads). Authed OpenPLC = upload-program RCE.
9. Distill (when confirmed): stage a GENERIC candidate - python3 scripts/wiki-stage.py --kind technique --slug <slug> --target-page techniques/mobile-iot/ics-scada-modbus.md.

Chaining

• HMI / Node-RED web app -> read the /api/state oracle and the register NAMES -> know exactly which Modbus address is the process variable and which is the interlock, instead of guessing blind.
• OpenPLC authed (default openplc:openplc) -> upload-program RCE on the SCADA host -> shell, not just process control. Prefer disabling protection over unauthenticated Modbus first (cheaper, no login grind).
• Danger state reached -> the payoff media (CCTV/HMI overlay) -> flag. The Modbus write is the pivot; the flag is in the frame (step 6).

Evasion

• Wrong unit/slave id looks like a dead PLC: if FC1-4 error out, scan unit ids (the modbus-discover "sid" value) before concluding the device is read-only or absent.

Lessons (THM Kaboom)

• The challenge NARRATIVE is the literal solve ("over-pressure the pump -> blow-out", "disable the protection"). Map each phrase to a Modbus write before chasing web creds.
• Coils 0-5 were inert; the safety kill-switch was coil 10 -> sweep WIDE (still bounded and reverting, per step 5).
• The OpenPLC login (openplc:openplc changed) was a rabbit hole that OOM'd the tooling host with a brute. Disable protection over Modbus instead.
• Flag was burned into the CCTV explosion video (/video?mode=explodedflag23), invisible to strings -> extract + view frames.

Confirmation gate

NOT confirmation: a Modbus/S7/EtherNet-IP port open and banner-grabbed; a coil/register/data-block you can only READ; an FC1-4 dump that returns values; the HMI showing a value you did not change; a write (FC5/6/15/16) that returned an ACK with no observed state change. A readable register alone proves reachability, not control.

IS confirmation (control/impact finding): a coil/register you WROTE whose effect is observed on the oracle - the HMI / Node-RED live-state flips to the intended (danger) state, the simulated process variable moves, or the interlock is demonstrably defeated - reproduced on a clean connection, culminating in the payoff (the flag the HMI/CCTV reveals). No observed effect = no control finding; log it as reachability at most.

An unauthenticated READ of OT state is a valid lower-severity finding in its own right (confirmed by demonstrating the unauth read), but it is NOT a control or physical-impact claim - keep the two separate.

Severity

Demonstrated impact	Rating
Unauth write to a safety-critical coil/register - physical impact, ESD or interlock bypass	critical
Unauth process-variable write (no safety bypass)	high
Unauth read of OT state (registers/coils/data blocks)	medium

Deadends

Append: - [ ] ICS <host> -- <proto> read-only / sim-only; no writable control coil found (swept 0-31)

Record the range you swept and whether an oracle existed, so the next pass does not re-run the same bounded probe.