Senior Product Security Engineer

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.

• 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)

• 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

• 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

• Play a critical role in developing cutting-edge ransomware protections and security features that will have a real-world impact.

• Work alongside highly skilled security researchers and engineering teams building next-generation security solutions.

• Have the opportunity to shape the process by which security innovations transition from research into real-world implementations.

• Be part of a company deeply committed to stopping ransomware and protecting customers.

• 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.

The Company reserves the right to modify or change these benefits programs at any time, with or without notice.​

Base Salary Range: $190k-$250k + 10% bonus + equity