App Security Expert

This position is listed on behalf of a partner company, which manages all applications and next steps. Our partner is looking for an App Security Expert based in United Kingdom. As an App Security Expert, you will help strengthen application security by designing realistic security test environments and evaluating vulnerabilities in traditional and AI-powered applications. You will focus on emerging security challenges associated with large language models (LLMs), including sensitive information disclosure and excessive agency. Through hands-on security engineering, you will develop deterministic test cases, create evaluation frameworks, and establish reliable methods for distinguishing vulnerable code from secure implementations. You will also contribute to advancing AI-powered static analysis and agent-based security architectures. Working in a remote, technically driven environment, you will collaborate with security specialists to refine testing methodologies and improve evaluation quality. This role is ideal for an experienced application security professional passionate about secure software development, AI security, and building practical solutions to complex cybersecurity challenges. Accountabilities - Design and implement purpose-built application fixtures containing representative security vulnerabilities or secure implementations, with a focus on OWASP risks affecting large language model applications. - Develop realistic test scenarios addressing critical LLM security concerns, including sensitive information disclosure, excessive agency, and related application security weaknesses. - Create deterministic test cases and comprehensive security-context manifests to evaluate application security posture consistently and reliably. - Develop detailed reference solutions and hidden answer keys that enable accurate evaluation of vulnerable versus secure code by AI systems and security scanners. - Assess and refine testing pipelines, ensuring synthetic security tasks are realistic, technically challenging, reproducible, and suitable for application security evaluation.

- Build, inspect, and secure application codebases, identifying advanced vulnerabilities and implementing appropriate remediation strategies. - Contribute to the design and evaluation of security architectures for traditional applications and agent-based systems. - Apply knowledge of AI-powered static application security testing (AI-SAST) and LLM security to improve automated vulnerability detection and assessment methodologies. - Document technical findings, testing approaches, security insights, and remediation recommendations in clear, precise, and actionable formats. - Collaborate with distributed teams through effective written and verbal communication, providing constructive feedback and reviewing peers' technical contributions. - Support the continuous improvement of security evaluation pipelines by identifying weaknesses, proposing enhancements, and validating new testing approaches. Requirements - Extensive experience in application security, secure software development, cybersecurity engineering, or a related field, ideally with at least 5 years of relevant professional experience. - Strong understanding of application security principles, secure coding practices, vulnerability assessment, and remediation techniques. - Familiarity with OSWE-level application security concepts, advanced vulnerability research, and practical security testing methodologies. - Solid knowledge of large language model security, including common LLM vulnerabilities, prompt-related attack vectors, sensitive information disclosure, and excessive agency. - Experience with AI-powered static application security testing (AI-SAST), automated code analysis, or AI-assisted security evaluation. - Proven ability to design, implement, secure, and test application codebases, including identifying complex vulnerabilities and validating secure implementations.