Product Security Engineer

Full-Time 37.5 hours, over 5 days (minimum 4 days per week in the office) About One Big Circle

Be part of an award-winning workplace:
The Sunday Times Best Medium-sized Technology Company 2025

Formed in 2017, One Big Circle is a fast-growing Bristol technology company that provides “Intelligent Video” solutions. We focus entirely on solving real-world industry problems by fusing new technology in the field of Video, IOT, Cloud and AI providing end to end solutions which allow our customers to dramatically improve their operational efficiency and safety. Our culture is one of high-quality technical delivery and we work at a speed that many industries are unaccustomed to;

we have done this by building a team dynamic that challenges and empowers our people and creating an environment where everyone contributes and learns. We are growing, profitable and have ambitious plans to continue expansion in and beyond our existing markets.

We are looking for a proactive and motivated individual to join our team to support the business in further growing our flagship award-winning product: AIVR. AIVR (Automated Intelligent Video Review) is a state-of-the-art video technology system used by thousands of people in the rail industry. AIVR has won dozens of awards and is recognised as the market leading solution, but we are building many more opportunities both in existing and new markets which will further accelerate our growth.

We have built a culture where people feel supported, included, and empowered to do their best work. Our team is growing, and we’d love for you to be part of the journey.

We are looking for a senior, hands‑on security engineer to own the security of our AIVR product stack end to end. You will spend your time thinking like an attacker, finding weaknesses in our systems before anyone else does, and then coordinating with the engineering teams to remediate.

You will pull the architecture apart, work out the realistic attack paths, test them, prove what's exploitable, explain the impact to the engineers who own them, help them work out a sensible fix, and then verify the fix.

This is a technical role in a team that likes getting things done. It is not a compliance or GRC position.

Your job is to make the product secure by continuously scouting for vulnerabilities and red teaming the AIVR product.

• Edge devices on trains. Embedded Linux devices with cameras and other sensors, fitted to in- service rolling stock. They are remote, physically outside our control, and connect back to us over 4G/5G.
• AWS cloud platform. A comprehensive and complex data processing platform, including serverless and containerised services developed predominantly in Python and hosting 7+ PB of Data.
• Web applications. The AIVR web applications used across the rail industry, with multi-tenant work spaces, sharing tools and integrations.
• Machine learning infrastructure. Training and inference workloads running in a 3rd party data centre.

• Continuously red team our product stack: threat modelling, penetration testing, code and configuration review, and adversarial thinking applied across devices, cloud, applications and ML infrastructure.
• Highlight findings and their impact. Work with the team that owns the system to explain findings and validate fixes.
• Input into AWS security architecture with the Platform team: IAM, organisation and account structure, networking, encryption, logging and detection.
• Evaluate device‑side security with the Device team: secure boot and update signing, credential and certificate lifecycle, remote access, tamper and theft scenarios.
• Harden the software supply chain: dependency and container vulnerability management, SBOMs, CI/CD pipeline integrity,…