Introduction
Welcome to this first writeup dedicated to MidnightCTF 2026! It took place remotely from March 13, 2026, 9 PM to March 15, 2026, 9 PM. It's a CTF I took part in with a team of 5. During this CTF, I focused on OSINT, my area of expertise.
This first challenge involves finding the location shown in the photo. A woman named Lin Xiayu was found dead there.
Initial Analysis
My first reflex is to use reverse image search tools such as Tineye, Yandex Images and Google Images. But we have an important piece of information: the location in the image is in China, so I'm also going to use Baidu Images alongside the other search tools.
However, the searches aren't conclusive:
Same result for the other tools.
But the image isn't our only lead! We have a username: LinXiayu35170.
If we analyze the username, a postal code precedes the woman's name: it's the one for Bruz, a town near Rennes. So I hypothesize that Lin studied in Rennes. I then looked into whether the city of Rennes had any ties with China, and I learned it has a twin-city partnership with the city of Jinan. Maybe Lin lives in Jinan, but I can't prove this hypothesis. So I set this information aside to search for social media platforms where Lin is registered under the name "LinXiayu35170".
To do this, I use the Whatsmyname tool:
So we have four results. I start by visiting Lin's Twitter account. This is probably the social network where she was active.
We notice the account only has one follower. We also note the profile picture is generated by thispersondoesnotexist and the account is very recent, common traits in OSINT challenges. This lets me conclude that this profile does indeed belong to Lin.
Lin posted three times:
I notice there's a comment on one of these tweets:
Nothing strange here, however, the user named Lucas Juillet is Lin's only follower. So I assume he knows her or is interested in her (judging by his odd comment).
Here again, we notice the same characteristics as Lin's profile: recent account, no activity, a username tied to cybersecurity and a photo widely used in the OSINT world: Mr Robot.
No doubt about it, Lucas Juillet plays a role in this challenge. So I decide to search for the username heaprunner on Whatsmyname.
Whatsmyname returns three results. I direct my search towards the GitHub account.
This account is also very recent, and has contributed to a single project: pattern-analysis
My teammates then noticed that the pattern_model.py file contains hidden information on line 9:
Lulu kicourt is also a username.
Whatsmyname didn't return any interesting results, so I decide to use another tool to get more information, Osint Industries.
I discover that lulu kicourt has a Strava account:
So I go to his profile: https://www.strava.com/athletes/206911898
We find a shared route:
A simple Google Maps search reveals that the finish line is at Zhaoyuan park.
Looking at the photos shared on Google Maps, we find a photo strangely similar to the one in the challenge statement:
We have indeed found the park where Lin's body was found!
Flag
