Rein Security, which develops runtime tools to secure enterprise AI agents and stop adversarial AI agents, raised a $25M Series A, taking total funding to $35M

Tools that protect your internal AI agents from being compromised become available and more robust.

Rein Security, a cybersecurity startup focused on protecting enterprise AI agents, has successfully closed a $25 million Series A funding round. This latest investment brings the company's total funding to $35 million. The round was co-led by Glilot Capital and Sienna Venture Capital, with contributions from Corner Ventures, Atlacle, and RNP Capital Advisors. Founded in 2024, Rein Security offers runtime tools designed to secure AI agents and defend against adversarial AI attacks. Their patented "sidecar" technology operates during agent execution, providing visibility into code and resource access, along with real-time guardrails. The company targets risks arising from the rapid deployment of AI agents with broad access to business systems. Rein Security reports significant growth since its product launch in January 2026, with an eightfold increase in revenue and a fivefold expansion of its customer base. The company's research has highlighted vulnerabilities in AI agents used by major retailers and enterprises, demonstrating the real-world risks of AI adoption outpacing security measures.

The substantial Series A funding for Rein Security underscores a critical market need for specialized AI agent security solutions. As enterprises accelerate AI integration, the inherent risks associated with autonomous agents accessing sensitive data and workflows are becoming increasingly apparent. Rein's focus on runtime security and its "sidecar" technology directly addresses the limitations of traditional cybersecurity frameworks, which are ill-equipped to handle the dynamic and self-directed nature of AI agents. This investment suggests a growing recognition that securing the AI supply chain and the agents themselves requires novel, real-time protection mechanisms beyond static analysis or perimeter defenses.

The increasing sophistication of AI-powered attacks, as evidenced by Rein's research, necessitates a proactive security posture. Companies that deploy AI agents must now contend with threats specifically designed to exploit these systems, such as prompt injection and adversarial manipulation. Rein Security's dual approach—securing internal agents while defending against external AI threats—positions it to capture a significant share of this emerging market. The company's rapid revenue and customer growth indicate strong market validation, signaling that more organizations will likely seek out specialized AI security platforms to mitigate burgeoning risks.