CTF Writeups

A collection of Capture the Flag (CTF) challenge solutions, covering topics such as network forensics, cryptography, web exploitation, steganography, general skills, and binary analysis.
Each folder contains a dedicated writeup with methodology, tools used, and final flag extraction.

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📂 Structure

🌐 Web Exploitation

• picoCTF - Old Sessions Exploiting misconfigured session expiration and public endpoints to perform Session Hijacking.
• picoCTF - Crack the Gate 1 Analyzing HTML comments, decoding ROT13 cipher, and injecting custom HTTP headers via curl to bypass authentication.
• picoCTF - SSTI1 Identifying Server-Side Template Injection (SSTI) in a Flask/Jinja2 application and escalating it to Remote Code Execution (RCE) to read server files.
• 04-web-len5
  Web exploitation challenge — exploiting type confusion in Express.js validation.

🔍 Forensics & Steganography

• 01-ftp-forensics
  FTP traffic analysis using Wireshark, packet filtering, and hex decoding to extract hidden flag.
• 02-dns-exfiltration
  DNS tunneling challenge — detecting exfiltrated data through custom queries.
• 06-hidden-cat
  Steganography challenge — extracting hidden flag from PNG image using LSB bit plane analysis.

⚙️ Binary Exploitation & Reverse Engineering

• 03-login-form-bof
  Binary exploitation challenge — abusing off-by-one overflow in C struct to gain admin shell.
• 05-weaponizedkey
  Reverse engineering challenge — analyzing obfuscated PowerShell script to reconstruct hidden API key.

🧠 General Skills & Automation

• picoCTF - Bytemancy 3 - Reverse engineering and network automation challenge — extracting function memory addresses from a compiled binary and automating dynamic responses with raw Little-Endian bytes via Python sockets.

(More challenges will be added as the repository grows.)

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🛠️ Tools & Techniques

Network & Forensics

• Wireshark & packet filtering
• DNS Tunneling detection
• Hex editors & string decoding
• CyberChef for decoding and analysis

Web Exploitation

• Cookie manipulation & Session Hijacking
• Server-Side Template Injection (SSTI) & RCE
• Express.js request handling & JSON manipulation
• Input validation bypass & Type confusion exploitation

Binary Analysis & Reverse Engineering

• Linux binary symbol analysis (nm, objdump)**
• Buffer overflow exploitation in C binaries (off-by-one)
• PowerShell reverse engineering & deobfuscation

Programming & Cryptography

• Python socket programming for dynamic network automation**
• Understanding Endianness (Little-Endian memory mapping)**
• Cryptography basics (hashing, encoding, ROT13)
• Steganography tools (stegOnline, steghide, zsteg, binwalk) with Bit plane analysis

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🎯 Purpose

This repository serves as:

• A learning resource for security enthusiasts.
• A portfolio showcase of practical problem‑solving in cybersecurity.
• A reference for common forensic and exploitation techniques.

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🔗 Author

Maintained by Nenad Bogdanović
GitHub: Nero265