Rein Security

Rein Security builds a runtime application-security platform that monitors application behavior inside live production environments rather than relying solely on pre-production code scanning. Customers add a single line of code to an application; within roughly a day the platform baselines normal behavior and then flags or “micro-sandboxes” deviations without killing processes or threads, an approach the company calls “inside-out” protection. Rein says the agentless architecture avoids proxies, sampling, or eBPF and adds under one millisecond of performance overhead, and it covers API security, SCA, SAST, DAST, and security for AI agents/MCP servers.

The company’s key differentiator is prioritizing actual production reachability and behavior over theoretical, pre-deployment vulnerability scoring — determining which flagged vulnerabilities are genuinely exploitable in the running application, and extending that same runtime lens to agentic AI workloads. Rein emerged from stealth on January 28, 2026, with an $8 million seed round led by Glilot Capital and participation from individual cybersecurity investors including Aqua Security founder Amir Jerbi and Orca Security CTO Yoav Alon. It was founded in 2024 by CEO Matan Bar-Efrat and CTO Netanel Rubin, both alumni of Israel’s Unit 8200, and operates out of Tel Aviv and New York with roughly two dozen employees. Named customers cited in launch coverage include insurtech firm Lemonade, whose CISO Jonathan Jaffe is quoted endorsing the platform’s production visibility.