Rein Security Raises $25 Million as Businesses Face New AI Security Risks
Cybersecurity startup Rein Security has raised $25 million in Series A funding to help businesses secure artificial intelligence agents that can independently interact with applications, access information and perform tasks across enterprise systems.
Announced on October 8, 2026, the investment brings the company's total funding 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.
The funding comes as companies increasingly integrate AI agents into customer service, software development, research, finance and other business operations. These systems can automate complex workflows, but their ability to take actions also introduces security risks that traditional software protection tools may not fully address.
What Is Rein Security?
Rein Security develops cybersecurity technology designed to monitor and control applications while they are running. The company has extended its platform to protect AI agents and the systems with which they interact.
Unlike an ordinary chatbot that primarily generates responses, an AI agent can use software tools, retrieve data, execute operations and carry out multi-step tasks. Depending on the permissions it receives, an agent may interact with customer records, internal databases, business applications or other sensitive resources.
Rein aims to provide businesses with visibility into these actions and establish controls that help prevent agents from performing operations outside their authorized roles.
How the AI Agent Security Platform Works
Rein's platform operates at runtime, meaning it monitors activity while an application or AI agent is executing tasks.
The company's approach is designed to help security teams understand what an agent is doing, identify potentially dangerous behavior and enforce rules before harmful actions are completed.
Key capabilities described by the company include:
- Action monitoring: Tracking agent activity and connecting actions to the underlying application code.
- Behavior controls: Applying rules that define which actions an agent is permitted to perform.
- Real-time protection: Blocking actions that violate configured security policies.
- Risk prioritization: Helping teams focus on vulnerabilities that could be exploited in real operating environments.
- Remediation support: Assisting security teams in addressing identified problems.
Rein says its architecture can provide these protections without routing company or customer data through an external gateway or proxy.
Why AI Agents Create New Cybersecurity Challenges
Businesses are increasingly moving beyond AI assistants that answer questions and toward agents that perform work with limited human intervention.
For example, an AI agent might review a support request, retrieve a customer's account details, prepare a response and update a business system. A coding agent might inspect software, modify files and run tests.
Each additional capability creates another potential point where permissions, instructions or system access must be managed carefully.
An agent could misunderstand a task, follow malicious instructions hidden in external content or attempt an action that exceeds its intended authority. If its permissions are too broad, even an accidental mistake could have consequences for a business.
These risks make it important to monitor what an agent actually does rather than relying exclusively on its written responses or the instructions provided to it.
Prompt Injection and Unauthorized Actions
One security concern involving AI agents is prompt injection. This occurs when malicious or misleading instructions are introduced through content an AI system processes, potentially influencing its behavior.
For instance, an agent reviewing a webpage or document could encounter instructions designed to make it disclose information or misuse an available tool.
Traditional security controls remain important, but they may not always be sufficient to understand the context of an AI agent's decisions and actions.
Runtime security systems seek to add another layer of protection by checking the actions an agent attempts to perform against established permissions and policies.
No single security product can eliminate every AI-related risk. Businesses still need appropriate access controls, secure software development, monitoring, testing and human oversight for sensitive operations.
Funding Will Support Product Development and Research
Rein Security plans to use its new capital to accelerate product development, expand its research into agentic security and recruit additional employees.
The company has identified its Agent Breakers research effort as one area that will receive investment. The work is intended to deepen research into the behavior and security weaknesses of AI agents.
The funding will also support expansion of its teams in New York and Tel Aviv.
With total disclosed funding reaching $35 million, Rein will have additional resources to develop its platform and pursue enterprise customers across different industries.
Companies Are Already Using AI Security Tools
Rein says its platform is already protecting thousands of AI agents that collectively perform millions of actions.
The company identifies Lemonade and Dun & Bradstreet among its customers. Its reported deployments span areas including financial services, healthcare, software-as-a-service, data, retail and energy.
These industries can involve sensitive customer information, financial operations and complex business workflows, making control over automated systems particularly important.
The company's deployment figures are based on its own disclosures and should not be interpreted as independent evidence that every AI agent is completely protected from cyberattacks.
The Market for AI Security Is Expanding
The growing adoption of AI agents is creating demand for security products designed specifically for autonomous systems.
Traditional cybersecurity tools remain essential for protecting networks, endpoints, identities and applications. However, agentic systems introduce additional questions about how software makes decisions, uses tools and moves information between systems.
Businesses need to understand not only whether an application contains a vulnerability, but also whether an AI agent can reach that vulnerability and use it during a real workflow.
Security platforms that can connect application behavior with the actions of AI agents may help organizations identify risks that are difficult to evaluate through static code analysis alone.
Competition in AI Cybersecurity Is Growing
Rein is entering a competitive market as cybersecurity companies develop products for AI applications and autonomous agents.
Established security vendors are adding AI-related protections to their platforms, while startups are building specialized systems for monitoring agent behavior, controlling tool access and identifying malicious activity.
The market's development will depend on how quickly businesses deploy autonomous AI systems, how well security products integrate with existing infrastructure and whether organizations can demonstrate measurable improvements in risk management.
Customers will also need to evaluate performance, compatibility, deployment complexity and the potential impact of security controls on legitimate AI workflows.
Why Human Oversight Still Matters
Real-time monitoring can help prevent unauthorized operations, but technical safeguards should not replace sound governance.
Organizations deploying AI agents should assign limited permissions, separate sensitive systems, log important actions and require human approval for high-impact decisions.
Businesses should also test agents against unexpected instructions and regularly review whether their permissions remain appropriate as their responsibilities change.
These measures can reduce the consequences of mistakes and make it easier to investigate suspicious activity when it occurs.
What Comes Next for Rein Security?
Rein's immediate priorities include improving its product, expanding research and hiring more staff. The company will also need to demonstrate that its platform can deliver reliable protection as enterprise AI deployments become more complex.
Its long-term opportunity is connected to a broader shift in business technology: AI systems are moving from simply providing information toward performing actions on behalf of people and organizations.
As that transition continues, security products will need to account for the behavior of autonomous software alongside the traditional risks associated with applications, networks and user accounts.
AI Innovation Needs Stronger Security
Rein Security's $25 million funding round highlights the growing importance of cybersecurity in the development of enterprise AI.
AI agents can help businesses automate repetitive work and coordinate complex tasks, but they also need carefully managed access to data and software tools.
By focusing on runtime monitoring and controls, Rein is attempting to address one part of this emerging challenge.
The company's future growth will depend on its ability to turn that approach into dependable protection for real-world business systems. More broadly, the expansion of AI agents is likely to make security, permissions and accountability increasingly important parts of enterprise AI adoption.
Journalist: Vijay Singh