Mobile Application Senior Security Engineer (Fintech)

Location: London, Milan, Stockholm, or Warsaw; most teams meet in the office 2–3 days per week

Salary: £91–£116,438 per year

Company

Klarna is building an everyday finance network serving over 120 million consumers across 26 countries.

What you will do

• Run penetration tests, red-team exercises, and vulnerability research against iOS and Android applications.
• Reverse-engineer mobile application binaries to identify sandboxing, permission, and platform-security weaknesses.
• Assess applications against the OWASP Mobile Application Security Verification Standard and Testing Guide.
• Evaluate and stress-test app-hardening and RASP protections.
• Partner with engineering teams to turn findings into fixes and follow remediation through to completion.
• Document vulnerabilities and recommendations in an actionable format for engineers.

Requirements

• Hands-on offensive mobile security experience through professional penetration testing, red teaming, bug bounty work, or security research.
• Experience assessing iOS, Android, or both.
• Understanding of mobile application sandboxing, permission models, and iOS and Android security architectures.
• Fluency with Frida, Objection, MobSF, jadx or apktool, Ghidra or Hopper, Burp Suite, and mitmproxy.
• Practical use of the OWASP MASVS and MASTG as a security assessment framework.
• Ability to work from one of the listed locations and attend the office 2–3 days per week for most teams.

Nice to have

• Experience securing fintech, payment, or banking applications.
• Experience with app-hardening and RASP solutions from offensive and defensive perspectives.
• Published CVEs, security research, conference talks, or mobile bug bounty achievements.
• Production mobile development experience.
• Familiarity with Play Integrity, App Attest, and device-binding schemes.

Culture & Benefits

• Co-located collaboration is valued, with office attendance varying by team and potentially changing over time.
• Diverse skills, perspectives, and backgrounds are welcomed.
• Final compensation depends on qualifications, skills, and experience.
• Applications should include a CV in English.