extension_tool_userscripts_unregister

THE RISK

Critical Risk

Why extension_tool_userscripts_unregister needs a policy

Unregistering userscripts removes them from the browser environment. This is an irreversible deletion action - once a userscript is unregistered, it is removed and would need to be re-registered manually. The ability to unregister by filter could affect multiple scripts at once, increasing blast radius. This qualifies as Destructive since it permanently removes configured browser automation scripts.

From the tool's definition Unregister userscripts by ID or filter

Documented attack patterns abuse exactly the kind of access extension_tool_userscripts_unregister gives an agent:

POLICY

How to control extension_tool_userscripts_unregister

PolicyLayer is an MCP gateway — it sits between your AI agents and WebMCP, and nothing reaches the server without passing your rules. This is the rule we recommend for extension_tool_userscripts_unregister:

policy.json

{
  "version": "1",
  "default": "deny",
  "hide": [
    "extension_tool_userscripts_unregister"
  ]
}

extension_tool_userscripts_unregister disappears from the agent's tool list entirely, and any attempt to call it is denied. The rest of the server keeps working.

Create a free account and register WebMCP — nothing to install.
Add this policy — paste it, or build it visually.
Point your MCP client (Claude, Cursor, anything) at your gateway URL.

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EXPLORE

Related tools and policies

More WebMCP tools

Execute call_extension_tool Execute a browser extension tool. Use this to call extension tools that provide browser-le Execute call_website_tool Execute a tool from a website MCP server. Use this to call website-specific tools that you Execute extension_tool_userscripts_test_execute Test execute a script without registering it (Chrome 135+) Execute extension_tool_userscripts_configure_world Configure USER_SCRIPT world properties Execute extension_tool_userscripts_register Register a new userscript with Chrome userScripts API Write extension_tool_userscripts_reset_world Reset USER_SCRIPT world configuration to defaults Write extension_tool_userscripts_update Update existing userscripts Read extension_tool_check_available_apis Check which Chrome Extension APIs are available to the extension

All 13 WebMCP tools →

Destructive tools on other servers

Android Forensics ADB MCP Server create_full_backup 0xarchive web3_revoke_key Frida Game Hacking MCP clear_scan cPanel MCP Server clear_spam_box

Go deeper

Critical-risk tools in WebMCP → Every critical-risk tool this server exposes, in one view.
All critical-risk MCP tools → Every critical-risk tool across the catalogue, and the policy pattern that contains them.
The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Blast radius → How much damage one compromised or confused agent can do — and how to bound it.
Tool call approval → Approval gates on individual tool calls: auto-allow, prompt, or deny.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about extension_tool_userscripts_unregister

What does the extension_tool_userscripts_unregister tool do? +

Unregister userscripts by ID or filter. It is categorised as a Destructive tool in the WebMCP MCP Server, which means it can permanently delete or destroy data. Block by default and require explicit approval.

How do I enforce a policy on extension_tool_userscripts_unregister? +

Register the Web MCP server in PolicyLayer and add a rule for extension_tool_userscripts_unregister: 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 WebMCP. Nothing to install.

What risk level is extension_tool_userscripts_unregister? +

extension_tool_userscripts_unregister is a Destructive tool with critical risk. Critical-risk tools should be blocked by default and only enabled with explicit human approval.

Can I rate-limit extension_tool_userscripts_unregister? +

Yes. Add a rate_limit block to the extension_tool_userscripts_unregister 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 extension_tool_userscripts_unregister completely? +

Set action: deny in the PolicyLayer policy for extension_tool_userscripts_unregister. 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 extension_tool_userscripts_unregister? +

extension_tool_userscripts_unregister is provided by the Web MCP server (miguelspizza/webmcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every WebMCP tool call.

Start from WebMCP, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.

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