Cas Van Cooten
Founder at Offensys
Utrecht, Utrecht, Netherlands
Summary
🤩
Rockstar🎓
Top SchoolCas Van Cooten is an offensive security professional and founder with nine years of hands-on experience conducting advanced red team engagements and building tooling to validate defenses. He co-founded Offensys to help security teams continuously validate controls through realistic attack simulations, and concurrently leads complex engagements at ABN AMRO where he researches and develops new offensive techniques. Cas is a prolific open-source contributor focused on exploitation and tooling—his work includes a proof-of-concept Follina RCE replicator, lightweight C2 implants in Nim, and automation for bug bounty reconnaissance. With an academic background in Business Informatics from Utrecht University, he blends technical depth in payload development, AV/EDR evasion, and infrastructure automation with a pragmatic focus on improving defenders’ visibility. Not obviously, he repeatedly translates offensive research into reusable, production-ready tooling that both demonstrates risks and accelerates defensive improvements.
9 years of coding experience
2 years of employment as a software developer
Gymnasium/Technasium Voortgezet onderwijs, Gymnasium/Technasium Voortgezet onderwijs at Gerrit Rietveld CollegeMaster of Science (M.Sc.) Business Informatics, Master of Science (M.Sc.) Business Informatics at Utrecht University
English, Dutch
Github Skills (47)
data-generation10
shellcode10
nim-lang10
develop10
injection10
inject10
python10
vulnerability10
r10
nucleo10
bash10
generator10
command-injection10
n10
nuclio10
Programming languages (13)
Github contributions (5)
chvancooten/NimPlant
Feb 2023 - Mar 2023
A light-weight first-stage C2 implant written in Nim (and Rust).
Role in this project:
Back-end Developer & Security Engineer
Back-end Developer & Security EngineerContributions:3 releases, 31 commits, 20 PRs in 27 days
Contributions summary:Cas focused on enhancing the Nimplant C2 implant's functionality and security. They added proxy support to the server, improving the handling of external IP addresses. The user fixed a critical bug within the registry command and implemented a screenshot command to facilitate data gathering. They also integrated a cleanup command and optimized detection rules, contributing to the project's maintainability and evasion capabilities.
chvancooten/maldev-for-dummies
May 2022 - Jul 2022
A workshop about Malware Development
Role in this project:Security Engineer
Security EngineerContributions:18 commits, 5 PRs, 12 pushes in 2 months
Contributions summary:Cas primarily contributed to implementing malware development techniques, specifically focusing on shellcode injection and AV evasion strategies. They developed C# and Nim implementations for shellcode injection, incorporating dynamic targeting and EDR evasion techniques such as XOR encryption. The user's work demonstrates a strong understanding of low-level system interactions and techniques to bypass security measures.
malwaremalware-developmentmethodologyworkshop
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