Lead Engineer — Application Security

Klarna; Greater London; On-site; GBP 90,000 - 130,000; Full time

Job summary

Klarna is seeking a Lead Engineer for Secure Development to help prevent security flaws by reviewing architecture, modeling threats, and guiding engineering teams in secure design and implementation.

The role involves hands-on assessment, code reviews, penetration testing, and building tooling to embed secure practices across Klarna's engineering division. Excellent English and collaboration with engineers are essential.

Qualifications

• Extensive experience reviewing architecture and threat models.
• Proficient coding in JavaScript/NodeJS, Python, Go, Java, or Scala.
• Strong knowledge of web/mobile/network security and cloud security.
• Excellent English communication and collaboration with engineers.

Responsibilities

• Perform threat modeling and architecture reviews for secure designs.
• Drive security improvements with engineering teams.
• Build and improve security tooling and automation.
• Conduct code reviews and penetration testing of Klarna services.
• Contribute to Klarna's internal security community.

Skills

Threat modeling

Architecture reviews

Code review

Penetration testing

Security tooling

Job description

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.

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

The Secure Development team equips Klarna's engineers to design, build, and deliver secure software through standardized tools and processes, continuous learning, and a security‑focused engineering culture. As a Lead Engineer on the team, you'll work on preventing security flaws before they reach production, not cleaning them up after.

That means getting involved early: reviewing architecture and design decisions, running threat models, and helping engineering teams build applications and services that are hard to break in the first place. You'll pair that upstream work with hands‑on assessment - code review and penetration testing - and with building the tooling and automation that make secure practices the path of least resistance across Klarna's engineering division.

What You'll Do

• You'll perform threat modeling and architecture and design reviews, helping teams design hard‑to‑break applications and services.
• You'll take an active role in architectural decisions, working directly with engineering teams to drive security improvements.
• You'll build and improve Klarna's security tooling, automation, and processes on an ongoing basis.
• You'll perform security assessments of Klarna services, including code reviews and penetration testing.
• You'll contribute to Klarna's internal engineering security community.

Who You Are

• You take a pragmatic approach to solving security issues, weighing effort against effect rather than chasing theoretical risk.
• You break down complex systems, spot where they're likely to fail, and land on fixes that work in practice.
• You've written and reviewed code in at least one of: JavaScript (NodeJS), Python, Go, Erlang, Java, or Scala.
• You're proficient across several of web application security, mobile application security, network security, operating system internals and hardening, applied cryptography, and cloud computing - and you're an expert in at least one of them.
• You have working proficiency in English.

Bonus points for

• Experience with BugBounty programs or CTF competitions.
• Communication skills that hold up when explaining security tradeoffs to engineers who don't work in security day to day.

Things you should know before applying

• This position works cross‑functionally across Klarna's engineering division, not within a single product team.
• We welcome candidates from non‑traditional or self‑taught security backgrounds - what matters is what you've built, broken, or fixed, not how you got there.

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!