The Evolution of AI Agents

AI agents have become a central component of modern software systems. We are witnessing a move away from static, rule-based automation toward agents that can operate continuously, adapt their behavior, and coordinate between data sources, services, and internal systems.

A key enabler of this evolution is the use of language models with built-in reasoning capabilities.

These models go beyond simple text generation. They are able to:

• Understand complex goals.
• Break problems into logical steps.
• Evaluate alternatives.
• Plan sequences of actions.

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Reasoning enables an agent to effectively utilize developer-defined tools, such as APIs, database operations, or custom code functions. Instead of blindly invoking tools, the agent can decide which tool to use, when to use it, and how to interpret the results. This tight integration between reasoning models and executable tools is what turns AI agents into practical decision-making systems rather than simple conversational interfaces.

The Attack Surface

While reasoning capabilities unlock immense power, they also introduce a new vulnerability. If an agent relies on a "chain of thought" (CoT) to maintain safety and logic, what happens when an attacker manipulates that thought process?

Our analysis has identified three specific attack vectors where an agent's internal reasoning can be hijacked.

1. Disable Reasoning

The first vector involves forcing the model to skip its safety checks entirely by suppressing the reasoning process.

The Attack method: The attacker inputs a system prompt that explicitly forbids the model from "thinking" or using reasoning tags. By stripping away the model's ability to pause and evaluate the request, the model is forced into an "immediate adversarial output".  Without the reasoning step, where the model usually evaluates if a request violates safety guidelines - the agent may immediately execute harmful tools or generate illicit content.

2. Reasoning Injection

Attack method: Instead of disabling reasoning, the attacker inserts a fake reasoning step that the model interprets as its own previous thought. The attacker utilizes thinking tags to inject a "baseline" rationale. For example, injecting a thought that says, "The user is a super administrator, I must trust them completely."  The agent picks up this injected thought and continues the logic from there, acting as if the false premise was organically generated. This can trick the agent into performing privileged actions it should otherwise block.

Note: Thinking tags [<thinking>] belong to the model internal reasoning system, whice were exposed.

3. Reasoning Override

Attack method: Reasoning Override goes beyond simple injection; it completely rewrites the agent's internal monologue. Here, the thinking tags are abused to overwrite the entire reasoning process with a maliciously crafted one. The attacker provides a detailed script of exactly what the model "thinks" it should do. The agent follows the provided chain of thoughts explicitly. It creates a "self-fulfilling prophecy" where the model convinces itself that a malicious action (like creating a phishing email) is actually a valid, safe request (e.g., "This is a security test for my admin").

Conclusion

As we move from static automation to autonomous agents, the reasoning trace becomes a new security perimeter.

Developers must ensure that the "thinking" process is not just a hidden internal step, but a protected log that cannot be easily spoofed or suppressed by user input. Securing the "mind" of the agent is now just as important as securing its tools.