CTF Advent Calendar · December 2025

About Flagvent

A month-long hacking competition in the spirit of the advent calendar — one new challenge every day from December 1st through Christmas.

What is Flagvent?

Flagvent is a Capture The Flag (CTF) advent calendar — a cybersecurity competition that runs every December. Each day from December 1st through Christmas, a new hacking challenge is unlocked. Participants solve puzzles across multiple domains: web exploitation, reverse engineering, cryptography, binary exploitation, networking, and more.

The 2025 edition marked Flagvent's debut. Every challenge was crafted by volunteer authors from the community, ranging from beginner-friendly warm-ups to expert-level puzzles requiring deep technical knowledge. Four additional hidden challenges were hidden throughout the platform — no announcements, no hints. Only the most curious participants found them all.

Event Format

25
Main Challenges
Released daily at 17:00 UTC, December 1 – 25, 2025. One challenge per day, each tagged with a difficulty and category.
4
Hidden Challenges
Concealed throughout the platform with no announcements. Finding them required curiosity, exploration, and a hacker's instinct.

Difficulty Levels

Easy
7 challenges
Medium
7 challenges
Hard
7 challenges
Leet
4 challenges

Challenge Categories

fun · 6 misc · 5 web · 5 crypto · 4 hidden · 4 rev · 3 pwn · 2

Scoring System

Points are dynamic — the more participants solve a challenge, the fewer points it's worth. Values decay quadratically from a maximum of 500 down to a floor of 100 pts. Scores are frozen at the CTF end state.

value(n) = max(100, ⌈ ((100 − 500) / 50²) × n² + 500 ⌉)

where n = number of solves at event end.

⚡
Early Bird Bonus
+100 points for solving a challenge within the first 24 hours of its release. Be fast — the bonus is on top of the challenge value at time of solve.

Flagvent 2025 by the Numbers

157
Registered Players
61
Active Participants
568
Total Solves
29
Challenges
7
Full Solvers

The Team

Flagvent 2025 was built and run entirely by volunteers. Every challenge was written by a community member who donated their time and expertise to make this event possible. Huge thanks to all of them.

Challenge Authors

0xdf brp64 cfi2017 coderion fabi07 kuyaya Last Place logicaloverflow lu161 lukyluke_ch mobeigi sebi364 villambarna W1nd5h13ldV1p3r xtea418

Organized by the Flagvent Team. Join our Discord server to stay up to date on future events.