Rein Security, a cybersecurity startup developing real-time protection for enterprise AI agents, has raised $25 million in Series A funding, bringing its total financing to $35 million.
The round was co-led by Glilot Capital and Sienna Venture Capital, with participation from Corner Ventures, Atlacle and RNP Capital Advisors.
Founded in 2024 and co-headquartered in New York and Tel Aviv, Rein Security develops technology to help enterprises monitor and control AI agents operating across business systems.
Monitoring AI Agents as They Execute Actions
Rein Security’s platform addresses two security challenges: protecting AI agents deployed by enterprises and defending against AI-driven attacks.
The platform uses patented sidecar technology that operates at runtime, allowing security teams to monitor agents while they execute tasks. It provides visibility into the code agents run and the resources they access, while applying real-time controls designed to prevent harmful actions.
Unlike approaches that route traffic through a gateway or proxy, Rein Security says its technology provides these capabilities without redirecting company or customer data. The platform also monitors risks associated with the AI agent supply chain.
The company reports detecting and blocking an attempted prompt injection involving an enterprise onboarding agent. The agent encountered malicious instructions hidden inside a PDF document, which attempted to redirect its behaviour beyond its intended role.
Rein Security has also demonstrated vulnerabilities in AI agents through its Agent Breakers research team. At Black Hat USA 2026, the team presented research showing how it compromised an AI shopping agent used by a major US retailer.
Revenue Growth and Enterprise Adoption
Since launching in January 2026, Rein Security says its revenue has increased eightfold and its customer base has grown fivefold.
The platform currently protects thousands of AI agents executing millions of actions. Its customers include Dun & Bradstreet and Lemonade, while Flex and Swimlane are among its newer customers.
At Lemonade, Rein Security protects AI agents supporting services used by more than three million active customers. At Dun & Bradstreet, its technology secures agents powering products used by more than 240,000 customers.
The company plans to use the Series A financing to accelerate product development, advance research into AI agent security and expand its team globally.