Writeup Bad Blood - UIUCTF 2025

Introduction

This is a follow-up OSINT challenge. Mr. Blue Sky is just trying his best to build a following, but he's been trying to hide interactions from a particular troll. Our goal is to investigate and find a flag by exploring Bluesky interactions.

Solution

To approach this, we used the tool blue.mackuba.eu, which allows us to see all interactions in a Bluesky thread. Since we know Mr. Blue Sky is trying to hide interactions from a specific troll, a good guess is to check who quoted the only post made on his profile.

By inspecting the quotes of that post on blue.mackuba.eu, we find this profile.

Going to the "Feeds" section of this profile, we can spot our flag.

uiuctf{bU7_1m_4_c4pr1c0rn_7098743}