Senior Security Engineer - xStocks

THE TEAM

xStocks brings real-world assets on-chain as tokenized securities that are regulated, fully-backed, and tradable across multiple blockchains. Built within Payward, the xStocks team runs the infrastructure that issues, custodies, and settles these instruments across EVM, Solana, TON, Tron, and more. The platform moves real value, so security is not a feature bolted on at the end. It is a property of everything the team ships. This is a hybrid engineering and security seat built for someone who is genuinely both: you ship products alongside the engineering team when the security queue is quiet, and you own security work end to end when it lands. You report into engineering and partner closely with the Payward security, CISO, and compliance functions.

THE OPPORTUNITY

- Own security deliverables end to end. Coordinate and review smart-contract audits, respond to security questionnaires and due-diligence requests, support CISO and compliance initiatives, and turn findings into tracked, closed-out fixes.

- Run offensive assessments against our own platforms. Pentest the web apps, APIs, backend services, and on-chain components, and build the tooling to do it repeatedly rather than once.

- Continuously assess posture. Threat-model new and existing systems, review architecture and key-management flows, and maintain a living view of the risks and their mitigations.

- Review code for security. Be a default reviewer on changes touching auth, cryptography, custody, signing, and fund movement across our chains.

- Harden the platform. Improve secrets handling, IAM and least-privilege, dependency and supply-chain hygiene, and detection and logging for security-relevant events.

- Secure custody and signing workflows. Review and harden transaction signing flows, MPC and HSM integrations, signer permissions, admin roles, approval policies, and break-glass procedures.

- Contribute to product engineering. Pick up regular backlog work in TypeScript so you stay close to the codebase you are defending.

- Support incidents. Help with detection, triage, response, and post-mortems, and feed the lessons back into the program.

WHAT YOU BRING

- An engineer first. You write and review production code comfortably, TypeScript and Node.js in our stack, and you understand systems deeply enough to break them.

- Strong application and infrastructure security fundamentals. The OWASP-class vulnerability landscape, authn and authz, injection, SSRF, supply-chain risk, and secure design. You have done real offensive work in pentesting, vuln research, or red-team.

- Applied cryptography and blockchain security. Symmetric and asymmetric primitives, hashing, signatures, and key management, plus the security model of EVM, Solana, and ideally TON or Tron. You can read a smart contract and reason about how it fails.

- Ownership. You can take an ambiguous security item, an audit, a questionnaire, or an incident, and drive it to closure without being managed through it.

- Clear communication. You can explain a risk to engineers, to a CISO, and to an auditor, and tailor the message to each.

- An automation instinct. You do not want to catch the same issue manually twice, so you turn findings into tests, alerts, controls, documentation, or platform improvements.

- Risk judgment. You can tell a theoretical issue from a material one, and communicate severity, likelihood, impact, and remediation tradeoffs clearly.

NICE TO HAVE

- Experience commissioning or remediating third-party smart-contract audits.

- Familiarity with custody and signing infrastructure such as HSMs, MPC, and ForDefi-style providers, and with on-chain transaction security.

- Cloud security depth in GCP or AWS, IAM, and container and runtime hardening.

- Detection engineering and security observability, including SIEM and log-based detections.

- Relevant certifications such as OSCP, OSWE, or GWAPT.

- Prior work in a regulated fintech or tokenization/DeFi environment.