write_string_with_keys_held

THE RISK

High Risk

Why write_string_with_keys_held needs a policy

This tool appears to type/write a string into the remote desktop while holding modifier keys (e.g., Ctrl, Alt, Shift), which constitutes a keyboard control action on a remote desktop. This is an Execute-category action as it triggers external operations on the remote system. Severity is high because arbitrary keyboard input with modifier keys held can trigger dangerous shortcuts or commands on the remote desktop.

From the tool's definition Tool name 'write_string_with_keys_held' on a VNC server that provides 'mouse and keyboard control, and automation'

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

POLICY

How to control write_string_with_keys_held

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

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "write_string_with_keys_held": {
      "limits": [
        {
          "counter": "write_string_with_keys_held_rate",
          "window": "minute",
          "max": 10,
          "scope": "grant"
        }
      ]
    }
  }
}

write_string_with_keys_held stays usable, but rate-capped — a runaway agent can't fire it dozens of times a minute. Everything else on the server is denied unless you say otherwise.

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

RATE-LIMIT THIS TOOL →

Free to start. No card required.

EXPLORE

Related tools and policies

More Vnc tools

Execute click_at_current_position click_at_current_position Execute click_at_current_position_with_keys_held click_at_current_position_with_keys_held Execute move_mouse_to Moves the mouse to the coordinates (x, y) in the VNC session's workspace. Execute move_mouse_with_keys_and_mouse_button_held move_mouse_with_keys_and_mouse_button_held Execute move_mouse_with_keys_held Moves the mouse from (start_x, start_y) to (end_x, end_y) while holding a number of keys. Execute move_mouse_with_mouse_button_held move_mouse_with_mouse_button_held Execute strike_keys strike_keys Execute strike_keys_with_keys_held strike_keys_with_keys_held

All 20 Vnc tools →

Execute tools on other servers

Android Forensics ADB MCP Server adb_shell_command EMBA-MCP run_emba_scan Frida Game Hacking MCP remove_breakpoint Procmon request_elevation

Go deeper

High-risk tools in Vnc → Every high-risk tool this server exposes, in one view.
All high-risk MCP tools → Every high-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.
Agent sandbox → Bounding what an agent can execute and where the boundary should sit.
Least privilege for MCP → Granting agents the minimum tool surface the task needs.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about write_string_with_keys_held

What does the write_string_with_keys_held tool do? +

write_string_with_keys_held. It is categorised as a Execute tool in the Vnc MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on write_string_with_keys_held? +

Register the Vnc MCP server in PolicyLayer and add a rule for write_string_with_keys_held: 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 Vnc. Nothing to install.

What risk level is write_string_with_keys_held? +

write_string_with_keys_held is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.

Can I rate-limit write_string_with_keys_held? +

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

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

write_string_with_keys_held is provided by the Vnc MCP server (regulad/vnc-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Vnc tool call.

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

CHECK YOUR STACK →