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Senior Software Engineer, Security

Flex· Engineering
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Remote$170k - $230kFull-timePosted 2mo ago

About the role

Senior Security Engineer role at Flex, reporting to the CTO, responsible for building product and infrastructure security in a fast-moving, AI-native private banking platform for business owners. Focus on securing money paths (ledger, card issuing, payouts, stablecoin), automating security checks, and reducing risk while maintaining velocity.

Responsibilities

  • Threat model the paths that move money: the ledger and write path, card issuing, payouts, and the stablecoin work.
  • Build secure-by-default infrastructure. Infrastructure as Code (IaC) guardrails, CI/CD supply chain integrity, secrets handling, service isolation, and workload IAM.
  • Build a just-in-time, least-privilege access system for cloud access that makes engineers faster while narrowing what any one credential can do.
  • Own application security across both new and existing systems. Continuously assess the highest-risk parts of what we've already shipped, and build automated checks and secure defaults into the development lifecycle so the same problems stop arriving. Code review on high-risk paths, dependency and SBOM hygiene, and static and dynamic analysis where it earns its keep.
  • Eliminate whole vulnerability classes; leave the instance-by-instance work to the machines.
  • Build a golden path that keeps sensitive data out of logs, and the tooling that proves it stayed out.
  • Run our vulnerability disclosure program end to end, and grow it into a bug bounty when we can triage at that volume.
  • Scope and manage external penetration tests, and drive the remediation afterwards.
  • Build security automation, including AI-assisted triage and review, so that two people can cover a surface that usually takes a larger team.
  • Partner with Engineering, IT and Corporate Engineering, Risk, and Compliance. You'll be technical input on partner security reviews and audits without owning the paperwork.

Qualifications

  • Substantial hands-on experience building or securing systems in a fast-moving environment, including a stretch where you were the most senior person doing this work.
  • Real software engineering ability in a language we'd ship (Python, Go, TypeScript, or similar). Not scripting alone.
  • Hands-on cloud infrastructure experience: AWS or GCP, Terraform or equivalent IaC, containers, and CI/CD pipelines you've changed, not only used.
  • Practical threat modeling on systems with real consequences, and the judgment to know which findings matter.
  • Experience with secrets management, workload identity, and service-to-service authorization.
  • Experience handling inbound vulnerability reports, including at least one difficult reporter.
  • Clear written communication and a bias toward writing things down.

Skills

Required:Threat modelingSecurity automationIaC / Cloud securityLanguages

Benefits

  • Flex offers medical, dental and vision insurance, paid time off, and a 401(k) plan.
Last updated Oct 21, 2026. Interested? Apply on the company site.

About Flex

All-in-One Business & Personal Finance Platform

Flex is the all-in-one business & personal finance platform for owners. Access premium business banking, flexible net-60 credit, and AP automation. All for free.

Business BankingBusiness CreditNet-60 Credit TermsRewards & CashbackEmployee Expense ManagementAP AutomationGlobal PaymentsCredit Card
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