DNS-Based Steganography

Overview

A Java reverse engineering challenge from DawgCTF that hid a flag inside DNS TXT records. The challenge required decompiling Java bytecode and understanding the steganography scheme used to encode data within DNS queries.

Approach

1. Decompiled the provided .class file to recover the Java source
2. Analyzed the DNS query construction logic
3. Identified the steganographic encoding within TXT record payloads
4. Wrote a decoder to extract the hidden flag

Key Techniques

• Java bytecode decompilation
• DNS protocol analysis
• Custom steganography decoding

Flag

🏴 DawgCTF{J@v@_My_B3l0v3d}

Takeaway

DNS is often overlooked as a data exfiltration channel. TXT records can carry arbitrary data, making them a popular vector for steganography and C2 communications.