Security Engineer, Offensive Security

Fluidstack; Greater London; On-site; GBP 167,000 - 205,000; Full time

Job summary

Fluidstack is seeking a seasoned security professional to lead red team and offensive security initiatives across modern data-center and cloud environments. You will emulate threat actors, test networks and applications, and break into multi-tenant systems to drive robust security improvements.

We value expertise in cloud platforms (AWS/GCP/Azure), Kubernetes, and CI/CD, plus hands-on coding in Python or Go to build custom tooling.

Qualifications

• Hands-on experience in red teaming and offensive security.
• Expertise in at least two areas: networks, OT/ICS, web/API apps, cloud, Kubernetes, CI/CD.
• Proven ability to find novel attack paths and chain vulnerabilities across boundaries.
• Experience running red team operations in well-defended environments.
• Experience finding authentication, authorization, and multi-tenant flaws in web apps and APIs.
• Proficiency in Python or Go and building tooling when off-the-shelf tools fall short.
• Experience using AI to speed up recon, vulnerability discovery, exploit development, or attack-path analysis.

Responsibilities

• Run red and purple team operations emulating advanced threat actors across our networks, data center OT, and applications.
• Pen test the networks behind our GPU clusters, from frontend and backend fabrics to out-of-band management and site connectivity.
• Test data center OT, including building management, power monitoring, cooling controls, in partnership with site operations.
• Break the customer-facing platform, including the console, public APIs, and identity and access controls.
• Assess internal and employee-built applications and the CI/CD pipelines that ship them.
• Partner with security and engineering on AI-specific attack scenarios and contribute to AI-assisted offensive testing tools.
• Present findings to technical and executive audiences as clear, actionable risk that shapes the security roadmap.

Skills

Red teaming

Offensive security

Cloud (AWS/GCP/Azure)

Kubernetes

CI/CD pipelines

Threat modeling

Python

Go

Job description

About Fluidstack

We exist to make humanity more free. For most of human history, you farmed or you starved. Technology gave people more time for the things they wanted to do, instead of things they had to do. Powerful AI will be the biggest lever for human choice we've ever built - but only if models are aligned with what humanity actually wants. There are groups building AI who don’t share these goals. Whoever deploys frontier compute infrastructure fastest will decide whether AI expands human freedom or shrinks it. We’re singularly focused on delivering 10 to 100s of GWs of compute faster than anyone else, rethinking every layer of the stack. We acquire power, design and build data centers, and operate them - with teams spanning hardware and software. Speed and scale are our key differentiators. Come be a part of building civilization‑scale infrastructure for AI.

We hire people who care deeply about this problem space.

How We Operate

• Be a barrel. Full autonomy. Own things end to end, take on scope without being asked, no permission required to operate outside your core role.
• Insane urgency. We drive everything forward as fast as possible.
• Reason from first principles. Challenge every assumption. Zero analogy thinking, no egos, the best idea wins.
• Love of the game. The frontier of AI is the most interesting problem of our time. We put in long hours at high intensity to push the frontier forward.
• Build something that actually matters. If you’re going to spend your time, spend it on something that matters to the world.

The Security Team

Examples of key problems the team is working on

• You’re securing the frontier of AI. The model weights training on our infrastructure are the most valuable and most targeted artifacts in technology, and we’re standing up the compute to hold them faster than anyone ever has. A breach isn’t a leak, it’s the frontier walking out the door.
• Build the entire security program from scratch. Most leaders inherit someone else’s system and spend a career patching it. Here you own it end to end, bare metal to boardroom, as we scale across continents.
• Your threat surface is measured in gigawatts. The customers running on our infrastructure are building the most consequential technology in human history, and being responsible for the physical and logical security of that work makes everything else feel small.

Role Scope

• Run red and purple team operations emulating advanced threat actors across our networks, data center OT, and applications, extending the offensive program alongside the team’s other specialists.
• Pen test the networks behind our GPU clusters, from frontend and backend fabrics to out-of-band management and site connectivity, with a focus on segmentation and tenant isolation.
• Test data center OT, including building management, power monitoring, cooling controls, and the IT/OT boundary, in partnership with site operations so testing never puts a live site at risk.
• Break the customer‑facing platform, including the console, public APIs, and identity and access controls, hunting for any path from one tenant to another.
• Assess internal and employee‑built applications and the CI/CD pipelines that ship them, and turn recurring findings into secure defaults engineers adopt.
• Partner with security and engineering teams on AI‑specific attack scenarios, including agentic systems and other novel AI‑enabled risks, and contribute to AI‑assisted offensive testing tools and workflows.
• Present findings to technical and executive audiences as clear, actionable risk that shapes the security roadmap.

What We’re Looking For

The below is a starting point. We always make space for exceptional people, so if you don’t fit this role exactly, tell us where you.

• You have years of hands‑on experience in red teaming and offensive security operations.
• You have deep expertise in at least two of: enterprise and data center networks, OT/ICS, web and API applications, cloud (AWS, GCP, Azure), Kubernetes, CI/CD pipelines.
• You’ve found novel attack paths and chained vulnerabilities into full compromise, crossing network, application, and identity boundaries to get there.
• You’ve run red team operations and adversary simulations against well‑defended environments.
• You’ve found authentication, authorization, and multi‑tenant flaws in web applications and APIs through hands‑on testing.
• You write quality code in Python, Go, or similar languages, and you build your own tooling when off‑the‑shelf tools fall short.
• You’ve put AI to work in real offensive engagements, using LLMs and agents to speed up recon, vulnerability discovery, exploit development, or attack‑path analysis.
• You write findings that get fixed, and you’ve worked closely with blue teams to turn your operations into detections and hardening.
• Bonus: State‑nexus threat models (frontier AI, government, critical infrastructure). Data center facility systems (BMS, EPMS, cooling controls, Modbus, BACnet). High‑performance and data center networking (InfiniBand, RoCE, BGP, out‑of‑band management). Testing AI and ML systems (agentic workflows, model serving). Defensive experience (detection engineering, SIEM, EDR).

We are committed to pay equity and transparency.

Fluidstack is an Equal Employment Opportunity Employer. All qualified applicants will receive consideration for employment without regard to race, color, religion, sex, national origin, sexual orientation, gender identity, disability and protected veterans’ status, or any other characteristic protected by law. Fluidstack will consider for employment qualified applicants with arrest and conviction records pursuant to applicable law.

Compensation Range: $224K - $275K