Senior Product Security Engineer

Halycon • Seattle, WA

42d • Remote

About The Position

Halcyon's goal is to deliver an anti-ransomware solution that breaks new ground in what a security product can achieve. Aligned with this mission, we're hiring a Senior Product Security Engineer to ensure our most innovative defenses make it into every release. These cutting-edge capabilities will keep our customers ahead in the fight against ransomware.

Requirements

• 5+ years in product security or endpoint-focused consulting, with hands-on testing of Windows-based agents or EDR/AV products
• Experience building fuzzers or integrating existing fuzzing frameworks for native code
• Experience and capability in building automated test harnesses from the ground up
• Strong Windows OS internals knowledge, especially user-mode hooking and Win32 API behaviors
• Proficient in C/C++ and Python, with solid experience calling with Windows APIs
• Experience reviewing and validating security findings
• Comfortable researching and suggesting security features end-to-end and creating technical content

Nice To Haves

• Rust development experience, particularly around FFI or unsafe code
• Published tooling or research in vulnerability discovery, fuzzing, and/or automated test frameworks
• Hands-on experience with CI platforms (GitHub Actions, Jenkins) to automate security workflows

Responsibilities

• Endpoint Hardening & Testing
• Design and implement security test harnesses from scratch to simulate real-world ransomware behavior
• Develop and integrate fuzzers (libFuzzer, AFL/WinAFL, or custom tools) for automated crash and vulnerability discovery
• Build user-mode hooking instrumentation and explore EDR bypass techniques to exercise agent internals
• Vulnerability Research & Triage
• Triage, reproduce, and analyze security findings against our agent and libraries
• Perform root-cause analysis on crashes or logic flaws; build minimal PoC exploits or reproducer cases
• Platform Expertise
• Deep understanding of Windows internals (ring transitions, memory management, Win32 API) with focus on user-mode security hooks
• Collaborate on driver-level or API-level integrations when necessary (no kernel-driver dev required)

Benefits

• Comprehensive healthcare (medical, dental, and vision) with premiums paid in full for employees and dependents.
• 401k plan with a generous employer contribution.
• Short and long-term disability coverage, basic life, and AD&D insurance plans.
• Medical and dependent care FSA options.
• Flexible PTO policy.
• Parental leave.
• Generous equity offering.

What This Job Offers

• Job Type: Full-time
• Career Level: Mid Level
• Education Level: No Education Listed
• Number of Employees: 101-250 employees