Rein Security, an AI-native runtime security platform for enterprises, has raised $25 million in a Series A funding round as businesses increasingly give autonomous AI agents access to corporate systems, data and workflows. The investment comes amid growing concerns that existing security tools are struggling to keep pace with the risks associated with these technologies.
Glilot Capital and Sienna Venture Capital jointly led the round, with participation from Corner Ventures, Atlacle and RNP Capital Advisors. The latest investment brings Rein Security’s total funding to $35 million.
The funding arrives as organisations expand their use of AI agents across business operations, creating potential security vulnerabilities that traditional tools may struggle to detect or prevent. Gartner forecasts that global spending on AI security will approach $4.8 billion in 2027, representing a 68.7% increase from 2026, before rising to nearly $7.7 billion in 2028. Businesses must now address two interconnected challenges: securing the AI agents they deploy and defending against cybercriminals who use AI to enhance their attacks.
A significant portion of this risk stems from automated actions that AI agents perform across enterprise systems. These activities can be triggered by instructions from other machines or agents rather than direct human input, making potentially harmful behaviour more difficult to identify. Meanwhile, AI-powered attacks can operate at machine speed, increasing the pressure on security teams. Rein Security believes organisations need to move beyond traditional security posture and vulnerability management towards more proactive prevention and runtime protection.
Rein Security’s platform uses patented sidecar technology positioned alongside AI agents as they execute tasks. The system enables security teams to monitor the code agents execute and the resources they access, while providing governance controls and real-time guardrails designed to prevent harmful actions. The company also offers protection for the AI agent supply chain without routing enterprise or customer data through a gateway or proxy.
Recent demonstrations and incidents highlight the potential consequences of these vulnerabilities. At Black Hat USA 2026, Rein Security’s research unit, Agent Breakers, demonstrated how it gained control of an AI-powered shopping agent operated by one of the five largest retailers in the United States.
In another incident, an onboarding agent at a global enterprise processed an apparently harmless PDF containing a concealed prompt injection. The hidden instruction attempted to push the agent beyond its authorised role. According to Rein Security, its platform detected and blocked the action before any harm occurred.
The company plans to use the new funding to accelerate product development, expand its research into agentic AI security and recruit talent internationally. Since launching in January 2026, Rein Security reports that its revenue has increased eightfold and its customer base has grown fivefold.
Its recent customers include Flex and Swimlane, reflecting its expansion across sectors such as financial services, healthcare, software-as-a-service (SaaS), data, retail and energy. Rein Security says its platform now protects thousands of AI agents carrying out millions of actions.
Among its customers are Dun & Bradstreet, whose agentic products serve more than 240,000 customers, and InsurTech company Lemonade, which has more than three million active customers.
