Rein Security raises $25M to rein in insecure AI agents

Rein Security Inc. said today it’s trying to help enterprises protect themselves against two distinct security threats relating to agentic artificial intelligence after raising $25 million in early-stage funding from Glilot Capital, Sienna Venture Capital, Corner Ventures, Atlacle and RNP Capital Advisors today.

The Series A round, which brings Rein’s total amount raised so far to $35 million, comes at a time when the risks of AI agents have become more acute than ever. In fact, the startup argues that autonomous agents bring two entirely new types of risks that enterprises have never had to deal with before, which means there’s no hope that their existing cybersecurity platforms are going to be able to protect them.

For enterprises that are adopting AI agents themselves, the big challenge is to secure those digital workers and make sure they don’t unwittingly cause problems or leak crucial secrets. And for everyone else, regardless of whether they’re using agents, they’re going to need to learn how to protect their information technology infrastructure from sophisticated, hacker-controlled agents, which are capable of continuously probing organizations’ defenses to search for vulnerabilities they can exploit.

Rein co-founder and Chief Executive Matan Bar-Efrat (pictured, left, alongside co-founder and Chief Technology Officer Netanel Rubin) told SiliconANGLE the main issue with autonomous AI agents is that the risks are completely new and therefore hidden from most security teams. For companies working with AI agents, the main danger is the downstream actions taken by those autonomous systems, which are usually based on instructions received from other systems and agents, rather than their human operators.

When AI agents are given a task to complete, they’ll strive to finish it no matter what, without thinking of the negative consequences their actions may have. To secure these agents, Bar-Efrat argues that companies need a way to understand every action they take so they can prevent the harmful ones from happening.

“Enterprise AI agents are becoming essential to how businesses operate, but security hasn’t kept pace with the autonomy these systems now have,” Bar-Efrat explained. “This funding enables us to keep building the infrastructure enterprises need to deploy AI agents with visibility, control and confidence.”

Rein Security tries to secure AI agents with a proactive approach that prioritizes prevention and protection at the execution layer with a platform that operates directly at runtime. Its platform is deployed as a lightweight sidecar that analyzes everything from the user’s prompts to the application programming interface calls and the database access.

It works by creating a baseline of each agent’s behavior, so it can understand what’s normal and what isn’t. Then it applies contextual, action-level controls that prevent deviations in real time, without shutting down the agent completely.

“Our approach is to micro-segment the resources that an agent can interact with and enforce controls at the point of execution,” Bar-Efrat explained. “We aren’t terminating the agent process, thread or the request, we only prevent the specific malicious action from taking place while allowing the rest of the workflow to continue uninterrupted.”

Rein’s understanding of agents’ baseline behavior is key, because there are so many ways that AI agents can be compromised that it’s basically impossible to prevent them all from occurring, Bar-Efrat said. Most agentic security tools are focused on identifying specific techniques and payloads used to compromise AI agents, such as indirect prompt injections, zero-day vulnerabilities in their code and misconfigurations that can allow unauthorized access or actions.

As far as Bar-Efrat is concerned, the method used by the attacker is irrelevant. What matters more is being able to understand an agent’s legitimate or normal behavior, so that any deviations from this can immediately be flagged.

“Attackers will continue to find new ways to manipulate AI systems, so rather than trying to predict every possible attack technique, Rein focuses on the agent’s behavior at runtime and the impact that an action could have on the enterprise,” he said.

Rein’s platform has already been deployed by enterprises such as Flex Ltd., Swimlane Inc., Lemonade Inc. and Dun & Bradstreet Holdings Inc. to secure thousands of new AI agents that are executing millions of actions each week. The company is also playing an important role in helping enterprises to understand the new risks AI presents. At Black Hat USA 2026 in August, its research team Agent Breakers showed how it was able to compromise the AI shopping agents of a top-five U.S. retailer, before detailing how that vulnerability can be prevented.

Rein has already grown its customer base by more than five-times this year, and the money from today’s round will help it to keep up that momentum by supporting a global hiring push and funding its product research.

Sienna Venture Capital’s Thomas Visan said the direct impact AI agents have in production environments means that companies cannot compromise on security a moment longer. “The frameworks that exist today are simply not equipped to handle this transition,” he said. “Rein’s differentiated platform explicitly addresses current, as well as new agentic AI security threats, giving the company a distinct position in this rapidly evolving market.”

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