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OverTheWire Bandit Level 9 Writeup — Extract Readable Text from a Mostly-Binary File

#security #beginners #ctf

data.txt is mostly binary data, but the password is one of the few human-readable strings inside it, preceded by several = characters — strings pulls out the readable text, and grep narrows to the marked line.

  • Platform: OverTheWire Bandit
  • Category: Linux Fundamentals
  • Level: 9 → 10
  • Difficulty: Beginner
  • Technique: strings + grep for a marker pattern

Challenge description

This file looks like garbage when opened directly — mostly non-printable binary bytes. Somewhere inside it, a handful of human-readable strings survive, and the level says the password is one of them, marked by leading equals signs.

"Level Goal: The password for the next level is stored in the file data.txt in one of the few human-readable strings, preceded by several '=' characters."

Step 1 — See why opening it directly doesn't work

Try viewing the raw file and notice it's mostly unprintable binary noise — cat or opening it in a plain editor produces garbled output:

file data.txt
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data.txt: data
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Step 2 — Extract just the readable text

strings scans a file and prints only the sequences of printable characters, skipping the binary noise around them:

strings data.txt
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(a short list of readable strings scattered among the output)
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Step 3 — Narrow to the marked line

The level told you the real string is preceded by several = characters — grep for a line starting with one or more of them:

strings data.txt | grep '^='
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========== [PASSWORD FOR bandit10]
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🔑 password intentionally hidden

The password is deliberately hidden — follow the method, you've earned it. 💪

Key takeaways

strings is the standard first move on any file that looks like binary garbage — it doesn't care what the file format actually is, it just reports every run of printable characters it finds. Combined with a targeted grep, it turns "needle in a haystack of binary noise" into a one-line command.

  • strings extracts printable text from any file, regardless of its actual format
  • ^= in a grep pattern anchors the match to the start of the line
  • This combination — strings piped into a targeted grep — reappears constantly in reversing and forensics challenges, not just this one

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