🔐 Linux CTF Challenges

Offensive Security Training - Professional CTF Challenges

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📖 About

This repository contains 9 professional-grade CTF challenges designed to test and develop critical Linux system administration and penetration testing skills. Each challenge focuses on real-world scenarios inspired by Offensive Security training materials.

Perfect for:

• 🎯 OSCP/PEN-100 exam preparation
• 💼 Linux system administrator skill development
• 🔒 Security researcher training
• 🎓 Cybersecurity students and professionals

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🚀 Quick Start

# Clone the repository
git clone https://github.com/sermikr0/Linux-CTFs.git
cd Linux-CTFs

# Make all scripts executable
chmod +x *.sh

# Run your first challenge
./build-script-symlink.sh

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📚 Challenge List

#	Challenge Name	File	Difficulty	Skills
1.1	Symlink Maze	build-script-symlink.sh	⭐⭐⭐⭐	Symlinks, Navigation
2.1	Command Line Puzzle	build-script-command-basics.sh	⭐⭐⭐⭐	Bash Scripting, Loops
2.2	History Forensics	build-script-history.sh	⭐⭐⭐⭐	Decryption, Forensics
3.1	Man Page RE	build-script-manual-page.sh	⭐⭐⭐⭐	Documentation, Parsing
4.1	Memory Forensics	build-script-filesystem.sh	⭐⭐⭐⭐⭐	Process Memory, /proc
7.1	Real-time Pipes	build-script-piping_and_redirection.sh	⭐⭐⭐⭐⭐	FIFO, Streaming
7.2	File Descriptors	build-script-piping_and_redirection_2.sh	⭐⭐⭐⭐⭐	FD Manipulation
8.1	Advanced Regex	build-script_searching_and_text_manipulation.sh	⭐⭐⭐⭐⭐	Regex, 1GB File
8.2	Binary Manipulation	build-script_searching_and_text_manipulation_2.sh	⭐⭐⭐⭐⭐	Binary Analysis

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🎯 Detailed Challenges

🔗 CTF 1.1: Symlink Maze Challenge

Navigate through a complex maze of symbolic links with circular references and broken links.

Flag: FLAG{symlink_maze_survivor}
Time: 30-45 minutes
Skills: ls, readlink, stat, find

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💻 CTF 2.1: Command Line Filename Puzzle

Extract flag from 1000 files where each character is hidden in the first letter of filenames.

Flag: FLAG{cli_scripting_legend}
Time: 45-60 minutes
Skills: Bash loops, grep, awk, cut, sort

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📜 CTF 2.2: Bash History Forensics

Decode 3-layer obfuscated command (Base64 → Hex → ROT13) hidden in 10,000+ bash history entries.

Flag: FLAG{history_forensics_expert}
Time: 30-60 minutes
Skills: base64, xxd, tr, multi-layer decryption

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📖 CTF 3.1: Man Page Reverse Engineering

Extract ASCII art flag from custom man page groff source code.

Flag: FLAG{man_page_reverse_engineer}
Time: 30-45 minutes
Skills: man, zcat, groff, text parsing

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🧠 CTF 4.1: Process Memory Forensics

Extract flag from running process memory using /proc virtual filesystem.

Flag: FLAG{proc_memory_forensics}
Time: 45-60 minutes
Skills: ps, /proc/[PID]/mem, strings, memory analysis

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⚡ CTF 7.1: Real-time Named Pipe Processing

Process 1000+ log entries per second through named pipe to decode 10 flag parts with different encodings.

Flag: FLAG{realtime_pipe_master}
Time: 45-60 minutes
Skills: mkfifo, Python, real-time processing, multi-encoding

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🔢 CTF 7.2: File Descriptor Manipulation

Navigate 7 nested subshells with custom file descriptors (FD 3-20) to collect flag parts.

Flag: FLAG{fd_manipulation_wizard}
Time: 45-60 minutes
Skills: exec, FD manipulation, process substitution, nested subshells

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🔍 CTF 8.1: Advanced Regex Master

Process 1GB log file with 50 flag parts using advanced regex patterns including lookahead, lookbehind, and backreferences.

Flag: FLAG{advanced_regex_overlord}
Time: 60-90 minutes
Skills: Python re, PCRE, lookahead/lookbehind, memory-efficient processing
⚠️ Requires 1GB+ disk space

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🔧 CTF 8.2: Binary Data Manipulation

Extract 5 flag parts from mixed binary file containing text, hex, base64, gzip, and XOR-encoded data.

Flag: FLAG{text_binary_manipulation_deity}
Time: 45-60 minutes
Skills: xxd, dd, base64, gzip, XOR decryption

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🛠️ System Requirements

Minimum Requirements

• OS: Linux (Kali Linux, Ubuntu, Debian)
• Disk Space: 2GB+ (1GB for CTF 8.1)
• RAM: 2GB minimum, 4GB recommended
• Permissions: sudo access required for some challenges

Required Tools

Most tools are pre-installed on Kali Linux:

# Verify installations
which gcc python3 base64 gzip xxd sed awk grep

# Install if missing
sudo apt update
sudo apt install -y gcc python3 coreutils gzip xxd

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📋 How to Use

Step 1: Run a Challenge

# Example: Start CTF 1.1
./build-script-symlink.sh

The script will:

• Display challenge information
• Create the CTF environment
• Show starting location
• Provide optional hints

Step 2: Solve the Challenge

Use your Linux skills to find the flag! Each challenge requires different techniques.

Step 3: Cleanup

# Always run cleanup when finished
/tmp/cleanup_ctf_X_X.sh

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💡 Solving Tips

General Approach

✅ DO:

• Read challenge descriptions carefully
• Check starting locations first
• Use man pages for command help
• Take notes on your approach
• Experiment in isolated environments

❌ DON'T:

• Skip cleanup scripts (can fill disk space)
• Use excessive sudo without understanding
• Give up too quickly - struggle builds skills!
• Run unknown commands without reading them first

Example Solutions

CTF 1.1 - Symlink Maze:

cd /dev/shm/.secrets/
ls -la
readlink link1
# Follow the chain to find the flag

CTF 2.1 - Command Line:

cd /opt/challenge/
for i in {001..026}; do 
    ls | grep "^.${i}_" | cut -c1
done | tr -d '\n'

CTF 4.1 - Process Memory:

ps aux | grep secret_daemon
PID=<found_pid>
sudo strings /proc/$PID/mem | grep FLAG

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🎓 Recommended Learning Path

Beginner → Intermediate

Start with these to build foundational skills:

1. CTF 1.1 - Symlink Maze
2. CTF 2.1 - Command Line Puzzle
3. CTF 3.1 - Man Page Reverse Engineering

Intermediate → Advanced

Progress to more complex challenges:

4. CTF 2.2 - History Forensics
5. CTF 4.1 - Memory Forensics
6. CTF 8.2 - Binary Manipulation

Advanced → Expert

Master the most challenging scenarios:

7. CTF 7.1 - Real-time Processing
8. CTF 7.2 - File Descriptors
9. CTF 8.1 - Advanced Regex (1GB)

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⚠️ Troubleshooting

Common Issues

Problem: Permission denied when running scripts

chmod +x build-script-*.sh

Problem: Command not found

sudo apt install -y <tool-name>

Problem: Out of disk space (CTF 8.1)

df -h /tmp
sudo apt clean

Problem: Challenge won't cleanup properly

# Manual cleanup
sudo rm -rf /tmp/ctf_*
sudo rm -rf /opt/challenge
sudo rm -rf /dev/shm/.secrets

Problem: Process still running after cleanup

ps aux | grep ctf
kill <PID>

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📊 Challenge Progress Tracker

Track your completed challenges:

• CTF 1.1 - Symlink Maze
• CTF 2.1 - Command Line Basics
• CTF 2.2 - History Forensics
• CTF 3.1 - Man Page Reverse Engineering
• CTF 4.1 - Process Memory Forensics
• CTF 7.1 - Real-time Pipe Processing
• CTF 7.2 - File Descriptor Manipulation
• CTF 8.1 - Advanced Regex
• CTF 8.2 - Binary Manipulation

🎉 Complete all 9 to become a Linux CTF Master!

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🤝 Contributing

Contributions are welcome! Here's how you can help:

Ways to Contribute

• 🐛 Report bugs or issues
• 💡 Suggest new challenges
• 📝 Improve documentation
• 🔧 Submit bug fixes
• ⭐ Star the repository

Contribution Process

1. Fork the repository
2. Create a feature branch (git checkout -b feature/new-challenge)
3. Make your changes
4. Test thoroughly
5. Commit (git commit -m 'Add new challenge')
6. Push (git push origin feature/new-challenge)
7. Open a Pull Request

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📜 License

This project is licensed under the MIT License - see the LICENSE file for details.

TL;DR: You can use, modify, and distribute this code freely. Just keep the license notice.

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🙏 Acknowledgments

Special thanks to:

• Offensive Security - For PEN-100 course inspiration
• Linux Community - For amazing tools and documentation
• CTF Community - For challenge design patterns and ideas
• Contributors - Everyone who helps improve these challenges

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📧 Contact & Support

Author: Sermikro CTF

Email: saidakbarxonmaqsudxonov4@gmail.com

Repository: github.com/sermikr0/Linux-CTFs

Get Help

• 🐛 Bug Reports: Open an Issue
• 💬 Questions: Use GitHub Discussions
• 📧 Email: saidakbarxonmaqsudxonov4@gmail.com

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⭐ Show Your Support

If you found these challenges helpful, please:

• ⭐ Star this repository
• 🔄 Share with others
• 🐛 Report issues
• 💡 Suggest improvements

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🎯 Final Words

"The best way to learn is by doing. These challenges will push your limits - embrace the struggle!"

Remember:

• 🔍 Read error messages carefully
• 📚 RTFM (Read The Fine Manual)
• 💡 Think creatively and outside the box
• 🧪 Experiment safely in isolated environments
• 🎓 Learn from every failure
• 🏆 Persistence beats resistance

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Version: 1.0.0
Last Updated: November 2025 Status: ✅ Production Ready

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Happy Hacking! 🎉