Rein Security Raises $25 Million to Protect Enterprise AI Agents

Rein Security, a platform designed to protect enterprises from risks posed by autonomous AI agents at runtime, has raised $25 million in a Series A funding round co-led by Glilot Capital and Sienna Venture Capital. Corner Ventures, Atlacle and RNP Capital Advisors also participated, bringing the company's total funding to $35 million.

The investment comes as businesses give AI agents broader access to corporate data, applications and workflows, creating security risks that traditional tools may struggle to detect or prevent.

Gartner forecasts that spending on AI security will reach approximately $4.8 billion in 2027, up 68.7% from 2026, before approaching $7.7 billion in 2028. Organizations must now protect the AI agents they deploy while defending against attackers who are also using AI.

Some of these risks emerge from automated actions performed by agents across enterprise systems, often triggered by instructions from machines or other agents rather than direct human input. AI also enables attackers to operate at machine speed, increasing pressure on security teams to move beyond vulnerability management toward prevention and real-time protection.

Rein Security's platform uses patented sidecar technology that operates where agents execute actions. It enables security teams to inspect every line of code executed by an agent and every resource it accesses, while providing governance controls and real-time guardrails to stop harmful behavior.

The platform also protects the agent supply chain without routing corporate or customer data through a gateway or intermediary agent.

At Black Hat USA 2026, Rein's research unit, Client Breakers, demonstrated how it took control of an AI shopping agent belonging to one of the five largest retailers in the United States.

In a separate incident, a setup agent at a global enterprise opened an apparently harmless PDF containing a hidden prompt injection. The instructions pushed the agent beyond its assigned role. Rein Security identified and stopped the action before any damage occurred.

The company plans to use the new funding for product development, agent-focused security research and international hiring. Since launching in January 2026, Rein Security has increased revenue eightfold and grown its customer base fivefold.

New customers include Flex and Swimlane, extending the company's reach across financial services, healthcare, software-as-a-service, data, retail and energy.

The platform now protects thousands of agents carrying out millions of actions. Customers include Dun & Bradstreet, whose agent-powered products serve more than 240,000 customers, and insurtech company Lemonade, which has more than three million active customers.

Matan Bar Efrat, Rein Security's co-founder and CEO, said enterprise AI agents had become essential to business operations, but security had not kept pace with their growing autonomy. He added that the funding would help the company build the infrastructure businesses need to deploy AI agents with visibility, control and confidence.