browser_set_cookies · MCProxy MCP: Risk & Policy

WHAT IT DOES

What browser_set_cookies does on MCProxy

AI agents use browser_set_cookies to create or update resources in MCProxy — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your MCProxy environment.

WHY IT NEEDS A POLICY

Why browser_set_cookies needs a policy

This tool writes cookie data into an active browser session, which can modify authentication state, session tokens, and other sensitive browser state. While reversible (cookies can be cleared), it can be misused to inject forged session credentials, hijack authenticated sessions, or bypass authentication controls — warranting a high severity rating.

From the tool's definition 'Set cookies in the browser session. Useful for restoring authentication state.'

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

browser_set_cookies Rate-limited

browser_set_cookies stays usable, but capped — an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "browser_set_cookies": {
      "limits": [
        {
          "counter": "browser_set_cookies_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches MCProxy, so you can run agents against it safely.

FAQ

Questions about browser_set_cookies

What does the browser_set_cookies tool do? +

Set cookies in the browser session. Useful for restoring authentication state. It is categorised as a Write tool in the MCProxy MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on browser_set_cookies? +

Register the MCProxy MCP server in PolicyLayer and add a rule for browser_set_cookies: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches MCProxy. Nothing to install.

What risk level is browser_set_cookies? +

browser_set_cookies is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit browser_set_cookies? +

Yes. Add a rate_limit block to the browser_set_cookies rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.

How do I block browser_set_cookies completely? +

Set action: deny in the PolicyLayer policy for browser_set_cookies. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.

What MCP server provides browser_set_cookies? +

browser_set_cookies is provided by the MCProxy MCP server (saladtechnologies/mcproxy). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.