send_file · Viber MCP: Risk & Policy

WHAT IT DOES

What send_file does on Viber

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

WHY IT NEEDS A POLICY

Why send_file needs a policy

This tool creates and transmits messages with file attachments, which is a reversible write operation. It modifies state by adding messages to a Viber conversation but does not delete, destroy, or execute arbitrary code. The 50MB size limit and forbidden extension list (exe, bat, vbs, cmd) show built-in safeguards against malware distribution.

From the tool's definition Tool sends file attachments to Viber users via the REST API. Description states 'Send a file attachment' and 'Returns message_token for delivery tracking', indicating message creation/transmission.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

send_file Rate-limited

send_file 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": {
    "send_file": {
      "limits": [
        {
          "counter": "send_file_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 Viber, so you can run agents against it safely.

FAQ

Questions about send_file

What does the send_file tool do? +

Send a file attachment (≤50MB) to a Viber user via public URL. Use for PDFs, documents, or spreadsheets. Forbidden extensions: exe, bat, vbs, cmd. Requires file size in bytes and filename with extension; ask the user if unknown. Returns message_token for delivery tracking. It is categorised as a Write tool in the Viber MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on send_file? +

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

What risk level is send_file? +

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

Can I rate-limit send_file? +

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

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

send_file is provided by the Viber MCP server (serhiizghama/viber-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.