Kolja Zuelsdorf
Software Security Engineer at powwow Berlin GmbH
Berlin, Germany
Summary
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Rockstar🎓
Top SchoolKolja Zuelsdorf is a software security engineer based in Berlin with 11 years of experience building backend systems, leading teams, and shaping security-focused features for SaaS and open-source projects. He currently works at powwow Berlin and has held senior technical and leadership roles including CTO at deinhandy.de, blending hands-on PHP development with operational and strategic responsibilities. A prolific contributor to notable open-source tooling—most prominently enhancements and test automation for Vimeo’s Psalm static analysis tool—he brings practical expertise in finding and fixing security and correctness issues in PHP codebases. His security work also includes engineering the Jetpack WAF, implementing IP allow/block lists and robust request handling logic. Comfortable in AWS-backed SaaS environments, Kolja prefers backend and security-focused roles and intentionally avoids frontend-heavy or purely commerce-driven companies. He’s pragmatic, detail-oriented, and motivated by projects that do something “awesome” rather than merely chase profit.
11 years of coding experience
9 years of employment as a software developer
Fachinformatiker, Anwendungsentwicklung, Fachinformatiker, Anwendungsentwicklung at TIXELmedia GmbHFachinformatiker, Anwendungsentwicklung, Fachinformatiker, Anwendungsentwicklung at balticCM, Wolfgang Winkler e.K.
English, Spanish, German
Stackoverflow
5,228reputation
833kreached
145answers
4questions
php
top-1%
Github Skills (25)
type-inference10
static-analysis10
waf10
testing10
wordpress10
it-security10
plugin10
security10
automation10
php10
automation-testing10
automations10
unit-testing9
security-testing9
security-scan9
Programming languages (14)
Github contributions (5)
Automattic/jetpack
Feb 2022 - Sep 2022
Security, performance, marketing, and design tools — Jetpack is made by WordPress experts to make WP sites safer and faster, and help you grow your traffic.
Role in this project:
Backend & Security Engineer
Backend & Security EngineerContributions:122 reviews, 18 commits, 30 PRs in 6 months
Contributions summary:Kolja primarily contributed to the development and enhancement of the Jetpack WAF (Web Application Firewall) feature. Their work included implementing IP allow and block lists, generating rules files, and creating standalone mode bootstrap functionality. Additionally, they were involved in refactoring the WAF's internal structure, and improving security-related aspects like IP address determination for request handling.
reactexpertswordpressphpsecurity
vimeo/psalm
Feb 2020 - Mar 2020
A static analysis tool for finding errors in PHP applications
Role in this project:Back-end Developer & Test Automation Engineer
Back-end Developer & Test Automation EngineerContributions:9 commits, 6 PRs, 13 comments in 18 days
Contributions summary:Kolja primarily contributed to the `psalm` PHP static analysis tool by implementing new functionality and improving existing features. Their work involved adding a function to calculate memory limits in bytes, and refactoring code related to this function. They also focused on test improvements by refactoring and creating new tests while addressing code style issues. Finally, the user fixed bugs by ensuring the stub files were loaded correctly, and improved the test setup for the `memory_limit` tests.
security-analysisfindingphptaint-analysisphp-applications
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