Senior Offensive Security Engineer
Klarna · Warsaw
Klarna, briefly
At Klarna, we're building an everyday finance network, helping over 120 million consumers across 26 countries save time and money, and worry less about their finances. Working here means taking on problems most companies never get to solve, and being hands-on enough that the interesting part of the work lands with you, not someone else — you'll build with AI, not watch it happen.
This is the stretch zone. Come find out what you're capable of.
About the role
Klarna runs a public Bug Bounty program and works with external pentest vendors year-round, which means a constant stream of real findings — and someone has to work out which ones matter, why, and what else might be affected by the same root cause. That's this position.
You'll sit on the Offensive Security team, running your own penetration tests against Klarna's internal and public-facing systems while also triaging what comes in from bug hunters, pentest vendors, and the SOC. When you find something, you won't stop at the one instance — you'll dig for variants across the codebase and infrastructure, and take what you learn back to the teams that own the code.
Klarna's stack runs Java and Node.js services on AWS in a microservice architecture, with third-party integrations added constantly — you'll need to keep pace with all of it, not just one corner.
What you'll do
You'll run white-box and black-box penetration tests against internal systems and public-facing applications.
You'll manage, triage, and investigate Bug Bounty submissions and external pentest findings.
You'll perform variant analysis on issues surfaced through any channel, tracing where else the same class of bug might exist.
You'll research and assess the security of Klarna's third-party solutions and integrations.
You'll build tooling for reconnaissance, automation, and metrics collection.
You'll guide developers, product security teams, and SOC investigations with hands-on expertise.
You'll run demos, workshops, and training that spread offensive security practices across Klarna.
You'll assess the security of Klarna's tech stack and help mature the security program overall.
Who you are
You've spent 5+ years running penetration tests and technical security assessments against production systems, not just lab environments.
You can read code and find real vulnerabilities in it, particularly in Java and Node.js.
You're comfortable operating in AWS and reviewing microservice architectures for security gaps.
You write up what you find so developers can act on it — clear findings tied to concrete remediation steps, not just severity labels.
You script your own tooling in Python rather than relying only on off-the-shelf scanners.
You push offensive security forward at Klarna on your own initiative, not just when assigned a ticket.
Bonus points for
Industry certifications such as OSCP, OSWE, CREST, GIAC, or an AWS security certification.
Active participation in CTFs or the broader security research community.
Public security research you can point to — CVEs, conference talks, or published tooling.
Things you should know before applying
This position is based in Klarna's Milan office; most teams currently meet in person 2–3 days per week, and this varies by team and can change over time.
Non-obvious backgrounds are welcome. Diversity of skills, perspectives, and backgrounds is how we create, innovate, and disrupt like no other.
Final compensation will be based on the candidate's qualifications, skills, and experience.
Please include a CV in English. Concrete beats comprehensive — what you built, what it did, what it cost.
Curious to learn more about Klarna and what it's like to work here? Explore our career site!