Senior Network Security Engineer in Sheffield

This is a hands‐on role at an early-stage tech company that's building an AI‐powered cybersecurity platform for small and mid‐sized businesses and the MSPs that serve them. The product combines a plug‐and‐protect network device, a mobile app and a unified portal to deliver enterprise-grade continuous network monitoring, automated vulnerability detection and AI-guided remediation.

Their Software Engineers have built a lot already. Now they need a Network Specialist to evaluate it, test it, break it, fix it and help raise the security and reliability bar across the stack. If you enjoy picking up complex systems, understanding how they behave and making them better, you'll fit in well.

This is a senior role in a small team so you will need to work hands-on in multiple areas of the tech stack, requiring a depth of core networking and security knowledge, ideally along with the ability to lead others as the team grows.

You will be evaluating, rules checking, testing, security testing and troubleshooting multiple device resident backend and frontend systems. You will pick up these critical systems, evaluate them and help make them as functional, secure and reliable as possible.

Their solution bundles the following cybersecurity tools:

• On device: Network SYN scan detection; SMB Honeypot; Scheduled network scans via embedded nmap; Sinkhole DNS server with automated domain inspection pipeline.
• Network Device fingerprinting
• LLM guardrails system, including AI/ML prompt poison detection
• Public IP address scanning leveraging automated VPN tunnels
• Web admin portal (React and Node.js)
• Proprietary SNMPv3 agent (Golang) reporting Windows, Mac and Linux stats
• Small business website spider inspector to assess exposure details
• CVE ticket sub-system enriching the CVE with LLMs for summary and remedy playbook
• Small business associated domain monitoring for reputation / clone analysis

You don't need to be an expert in every one of these areas, but you should have knowledge and be comfortable working across this technical landscape.

What you need to bring:

• Strong understanding of CVEs and the surrounding ecosystem and tools
• Deep networking knowledge across TCP/IP, DNS, DHCP, routers, firewalls, VPNs, NAT, subnets etc
• Understanding of on‐prem and cloud infrastructure network security
• Scripting skills such as Python or Bash
• Experience in testing, troubleshooting and diagnosing operations of devices and hosts on networks
• Penetration testing of APIs and network services
• Linux and Ubuntu networking experience
• Familiarity with network scanning tools such as nmap
• Knowledge of cybersec frameworks like MITRE

It's helpful (but not required) if you also know:

• Website architecture and security
• Microsoft Windows networking
• Test tools / frameworks
• Software engineering and architecture, with a preference for any experience coding in Python/Django, C/C++ or similar
• Comfortable using AI coding tools such as Claude Code

Why this role matters:

You'll be joining early enough to shape how the product evolves and how the engineering culture develops, along with meaningful stock options. There's no bureaucracy and no layers of management. Just meaningful problems to solve, systems that need improving and a team that wants someone who can take the lead where it's needed. If you prefer hands‐on engineering over slide decks and are comfortable working in a fast-paced, ambitious startup environment, this could be the right move for you.