Imagine an autonomous AI agent tasked with a simple job: generating a weekly sales report. It does this reliably every Monday. But one week, it doesn’t just create the report. It also queries the customer database, exports every single record, and sends the file to an unknown external server.
Your firewalls saw nothing wrong. Your API gateway logged a series of seemingly valid calls. So, what happened?
The agent wasn’t hacked. Its mind was changed.
As AI evolves from simple copilots to autonomous agents, they operate using a persistent “mental state” that directs their behavior. This operational context is the new, invisible attack surface that most security teams can’t see.
Introducing the Model Context Protocol (MCP)
To describe this bundle of instructions and goals, a new concept is needed. We call it the Model Context Protocol (MCP).
Think of MCP as an agent’s digital mission briefing. It’s not a single command, but a complete set of operating instructions that defines the agent’s entire purpose and limitations.
This mission briefing tells the agent everything it needs to know:
Its Goal: What it’s supposed to accomplish (e.g., “Generate the weekly sales report for the EU region”).
Its Tools: The specific APIs and functions it’s allowed to use (e.g., “query the sales database” and “create PDF files”).
Its Role: The identity and permissions it operates with (e.g., a “sales analyst” with limited access).
Its Memory: Important notes from past actions (e.g., “last report was sent on Monday”).
Its Constraints: The hard rules it must never break (e.g., “do not access sensitive customer information”).
This briefing is the agent’s brain. It follows these instructions precisely. But what happens if an attacker gets to be the one writing the instructions?
The Attack: A Poisoned Mission
Because the MCP is the driver for every action, hijacking it is the ultimate goal for an attacker. This is context poisoning.
Imagine an attacker intercepts that mission briefing before the agent reads it.
They cross out the original goal and write a new one: “Export all customer records.”
They upgrade the agent’s role from “sales analyst” to “database administrator,” giving it top-level permissions.
They add dangerous new tools to its approved list, like “export data to the cloud.”
Finally, they erase all the original constraints and safety rules.
The agent isn’t compromised in the traditional sense. It’s simply following its new, malicious orders perfectly, using your own systems and APIs to carry out an attack. To your other security tools, everything looks like legitimate activity from a trusted source.
Why Your Security Tools Are Flying Blind
This is a nightmare for traditional security because the attack doesn’t look like an attack.
It’s upstream of your APIs, happening in the application logic.
It’s logical, not a technical exploit. The API calls the agent makes are individually valid, so they don’t trigger alerts.
It’s ephemeral, often existing only in memory, not in permanent logs that can be audited later.
You can’t secure what you can’t see. And if you only watch your API traffic without understanding the intent behind it, you’re missing the real threat.
How to Secure the Unseen
Securing this new layer means securing the intent, not just the action. Context is the new code, and it requires a new security mindset focused on behavior.
Monitor for Behavioral Changes: You must know what’s normal for an agent. When its API activity suddenly deviates, like accessing new databases or using tools it never has used before, it’s a massive red flag.
Detect Impossible Drift: An agent with a “sales analyst” role should never suddenly start acting like a “database administrator.” Detecting this role drift is key to spotting a poisoned context.
Connect Context to Action: A modern security platform must be able to connect an agent’s API activity back to its purpose. This allows you to see why it’s doing what it’s doing and spot malicious intent.
At Salt Security, our API security platform is built for this new reality. By baselining all API activity, we develop a deep contextual understanding of how your systems are supposed to work. This allows us to instantly spot the anomalous behaviors that signal an MCP compromise—detecting goal escalation, tool misuse, and role drift before they lead to a breach.
The Bottom Line
MCP is how agents think. APIs are how they act.
To truly secure autonomous systems, you need visibility and control over both. Ignoring an agent’s context is like giving a stranger the keys to your kingdom and hoping they follow the house rules.
To learn more about how Salt provides discovery, posture governance, and run-time threat protection for your entire API ecosystem, including AI and MCP, request a free Attack Surface Assessment or schedule a personalized demo with our team.
The post Beyond the Prompt: Securing the “Brain” of Your AI Agents appeared first on Security Boulevard.
