6a0877384d
- Remove undeployed challenges: Phantom_Byte, Cr4cK_w1f1, Lain_Br34kC0r3 V1, Lain_VS_Knights, Lets_All_Love_UART, AETHER_NET, Last_Train_451, Web3/ - Sync 24 solve/ files from main CTF-Espilon repo - Update all READMEs with real CTFd final scores at freeze - Add git-header.png banner - Rewrite README: scoreboard top 10, edition stats (1410 users, 264 boards, 1344 solves), correct freeze date March 26 2026
73 lines
1.9 KiB
Markdown
73 lines
1.9 KiB
Markdown
# Anesthesia Gateway -- Solution
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## Overview
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MQTT broker simulating an anesthesia monitoring gateway. A debug topic leaks
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an encoded firmware blob. Reverse the encoding to extract a maintenance key
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and publish it to unlock the flag.
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## Steps
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### 1. Connect and discover topics
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```bash
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mosquitto_sub -h HOST -t "sainte-mika/#" -v
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```
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Topics discovered:
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- `sainte-mika/or13/vitals` -- patient vital signs (JSON)
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- `sainte-mika/or13/sevoflurane` -- anesthetic gas data
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- `sainte-mika/or13/propofol` -- infusion pump data
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- `sainte-mika/or13/ventilator` -- mechanical ventilator data
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- `sainte-mika/or13/alarms` -- alarm status (note: `"network": "WIRED-MED"`)
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- `sainte-mika/or13/debug/firmware` -- **base64-encoded blob (every 45s)**
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### 2. Capture firmware blob
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Grab the base64 string from `debug/firmware`.
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### 3. Decode the blob
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The encoding chain is: JSON -> zlib -> XOR("WIRED") -> base64
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To reverse:
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```python
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import base64, zlib
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blob = "<base64 string from MQTT>"
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raw = base64.b64decode(blob)
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# XOR with key "WIRED" (hint: WIRED-MED appears in alarm data)
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key = b"WIRED"
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xored = bytes(b ^ key[i % len(key)] for i, b in enumerate(raw))
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# After XOR, bytes start with 78 9C (zlib magic)
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config = zlib.decompress(xored)
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print(config.decode())
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```
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### 4. Extract maintenance key
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The decoded JSON contains:
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```json
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{
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"maintenance_key": "N4V1-C4R3-0R13-L41N"
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}
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```
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### 5. Publish key and get flag
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```bash
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mosquitto_pub -h HOST -t "sainte-mika/or13/maintenance/unlock" -m "N4V1-C4R3-0R13-L41N"
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```
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Subscribe to the flag topic:
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```bash
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mosquitto_sub -h HOST -t "sainte-mika/or13/maintenance/flag"
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```
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### Key insights
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- The XOR key "WIRED" is discoverable from the alarm topic which includes `"network": "WIRED-MED"`
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- After XOR decryption, the zlib magic bytes `78 9C` confirm the correct key
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- The maintenance key "N4V1-C4R3-0R13-L41N" = "Navi Care OR13 Lain" in leetspeak
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## Flag
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`ESPILON{mQtt_g4tw4y_4n3sth3s14}`
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## Author
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Eun0us
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