Senior AppSec Engineer: Pen-Testing & AI Security

Meetborderless; Greater London; Hybrid; GBP 142,000 - 177,000; Full time

Job summary

Brex is seeking a Senior Application Security Engineer to identify and remediate vulnerabilities across the Brex platform. You will perform code reviews, penetration testing, and tooling development to support secure developer workflows.

You will collaborate across Security Operations, GRC, Product Security, Front End Platform, and IT Infrastructure, applying threat modeling, SAST/DAST, and agentic AI security to protect a global financial service used by top customers.

Qualifications

• 5+ years work experience in an Application Security or related role.
• Ability to find vulnerabilities in complex systems, demonstrating business impact through custom attack chains.
• Experience with a wide range of secure development activities including - threat modeling, developer education, and incident response.
• Knowledge of Python, scripting languages, and AI/agentic workflows to automate tasks, build tools and improve productivity.
• Collaborative mindset paired with strong written and verbal communication skills.

Responsibilities

• Identifying vulnerabilities, demonstrating business impact, and articulating the risk of specific vulnerabilities to drive prioritization efforts
• Perform penetration testing and design reviews, looking for vulnerabilities and insecure designs, work with engineering and product to design secure product features
• Maintain and build internal tools to automate security efforts, perform SAST and DAST testing of the Brex platform, and support secure development practices
• Build and contribute to a culture of collaborative security excellence through technical leadership, learning sessions, and mentorship within the team and wider organization

Skills

Application security

Python

Scripting languages

Threat modeling

Communication skills

Tools

SAST

DAST

Kubernetes

Job description

Brex is seeking a Senior Application Security Engineer to identify and remediate vulnerabilities across the Brex platform. You will perform code reviews, penetration testing, and tooling development to support secure developer workflows.

You will collaborate across Security Operations, GRC, Product Security, Front End Platform, and IT Infrastructure, applying threat modeling, SAST/DAST, and agentic AI security to protect a global financial service used by top customers.