Here is my solution for the hard OSINT challenge Une aiguille dans une Île-de-France as part of the 2026 edition of the 404CTF held online by the French secret service (DGSE) and Telecom SudParis.



We are told that 2 threat actors are planning an attack towards a scientist to steal an award from her. They were traced and we are given the text message below, as well as a list of 1000 points of interest under points_d_interets.json :

Text message

I’ll be waiting for you by the small rectangular fountain on the sidewalk facing the café. Don’t forget your lock-picking kit !

We need to provide the name of the great female scientist living there.

Finding the location among all POIs

I started using Overpass turbo to shorten the list of POIs. Given the details provided by the text message, I wrote this query :

(
    node(around:500,48.683432,2.296373)["amenity"="fountain"];
    [...]
    node(around:500,48.895186,2.440037)["amenity"="fountain"];
)->.fountains;

node(around.fountains:100)["amenity"~"cafe|bar|restaurant"]["name"~"cafe|café", i];

out;

It looks for all fountains located in a 500-meter range around each POI. Given this list, all cafés located at 100 meters at most from a fountain are returned. This last filter is based on the word “café” in the name (case insensitive).

As a result, I got 22 nodes. I assumed “great female scientist” was too vague to be in Paris, so I focused on the 6 remaining nodes.

Overpass turbo results

I then had a look at each of them using Google Street View. The location that best matched the description from the text message is Labriz’ Cafe, in Viroflay.

Best location

The great scientist

I struggled a while to find a female scientist living in Viroflay …

… only to find out this basic Google Search was suficient 🥲 Google search

On page 11 of this journal, I found the following article : Article

🚩 Flag

404CTF{catherine-cesarsky}