The Numbers Mason from OSMOSIS - "For the Love of OSINT CTF"

Task Overview

We were given a WAV audio file that contained a sequence of sounds. The goal was to extract meaningful information from it.

Since the file was an audio signal, we suspected it might contain Dual-Tone Multi-Frequency (DTMF) tones, commonly used in telephony for dialing numbers. To decode it, we used an online DTMF decoder:

🔗 DTMF Decoder

The tool extracted the following numerical sequence from the audio:

224448555999#2886677727788

Initially, it looked like a sequence of phone keypad numbers, possibly representing text typed on a T9 keyboard (old Nokia-style SMS input). So we can user tool like Multi-tap Decoder.

By recognizing the input as T9-based text, we converted:

224448555999#2886677727788

to:

BITLY AUNRAQU

We figured out that it's a link to https://bit.ly/AUNRAQU

This link led to a website with a flag

Conclusion

The challenge involved decoding DTMF tones from a WAV file and recognizing the result as a T9 text message, which turned out to be a bit.ly link leading to a webpage with flag.