Writeups from Capture the Flag (CTF) events I participated in. About web, scripting, crypto, reversing and everything in between. All writeups include detailed explanations of how everything works.
x3CTF - blogdog (+ new CSS Injection XS-Leak!)
A "hard web xssbot" challenge about a fun browser quirk with the is= attribute to perform CSS Injection. Bypass the strict CSP with an unintended new technique to XS-Leak a selector's result by detecting the site crashing
IrisCTF 2025 - webwebhookhook
The hardest web challenge of this CTF was a simple Java Spring web server written in Kotlin, with a complex DNS Rebinding solution. Learn about a new way to exploit this when a response is cached by timing your payload with a cache invalidation
Wizer CTF May 2024
Complete 6 web challenges with source code in 6 hours. I ended up winning this CTF and finding an unintended solution in one of the challenges.
GCC CTF
An event organized by a French CTF team with many challenges in ranging various difficulties. We placed 11th in the end and most notably found a few different unintended solutions to solve challenges quicker.
HTB University CTF 2023
The yearly HackTheBox University CTF 2023: Brains & Bytes was an event for many universities worldwide, in which we as "Hanzehogeschool" placed 19th! Cool web challenges and standard categories, with their signature Fullpwn machines
Cyber Apocalypse 2023
Cyber Apocalypse 2023: The Cursed Mission by HackTheBox. A CTF full of unique and interesting challenges of the utmost quality
TU Delft CTF 2022
A beginner-friendly CTF organized by the Dutch TU Delft CTF team where anyone could participate, and me and some friends got 3rd place
Hacky Holidays Unlock the City 2022
An almost 3 week long CTF with beginner to hard challenges. Very high quality challenges with every week a new batch of challenges to try.
Challenge the Cyber 2022
A Dutch CTF event with a Training Mission to practice, and a real CTF after. Part of the European Cyber Security Challenge. The challenges were all high quality and good learning material
NahamCon CTF 2022
A yearly Capture The Flag event that was a part of NahamCon. The event lasted 48 hours, and had loads of challenges from different categories.
Cyber Santa is Coming to Town 2021
A 5-day long CTF, with a challenge of every category coming out every day. Challenges range from beginner to medium.
Google Beginners Quest 2021
A CTF hosted by Google, with some beginner/medium challenges
Cyber Apocalypse 2021
22 April is International Earth Day and guess what… The Earth was hacked by malicious extraterrestrials. Their ultimate plan is to seize control of our planet. It's only you who can save us from this terrible fate.
Other
Miscellaneous one-off CTF writeups