sys_base64 · Onion MCP: Risk & Policy

WHAT IT DOES

What sys_base64 does on Onion

AI agents invoke sys_base64 to trigger actions in Onion. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call — builds kicked off, notifications sent, workflows started.

WHY IT NEEDS A POLICY

Why sys_base64 needs a policy

This tool performs Base64 encoding or decoding, which is a data transformation operation. It doesn't purely read existing data (it transforms input), nor does it write to any persistent store. It executes a transformation/computation on provided text. The severity is low as it only processes text in memory with no side effects on external systems, though it could theoretically be misused to obfuscate data.

From the tool's definition Base64 编码或解码文本 (Base64 encode or decode text)

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

sys_base64 Rate-limited

sys_base64 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.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "sys_base64": {
      "limits": [
        {
          "counter": "sys_base64_rate",
          "window": "minute",
          "max": 10,
          "scope": "grant"
        }
      ]
    }
  }
}

RATE-LIMIT THIS TOOL →

Instant setup, no code required.

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

FAQ

Questions about sys_base64

What does the sys_base64 tool do? +

Base64 编码或解码文本。. It is categorised as a Execute tool in the Onion MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on sys_base64? +

Register the Onion MCP server in PolicyLayer and add a rule for sys_base64: 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 Onion. Nothing to install.

What risk level is sys_base64? +

sys_base64 is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.

Can I rate-limit sys_base64? +

Yes. Add a rate_limit block to the sys_base64 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 sys_base64 completely? +

Set action: deny in the PolicyLayer policy for sys_base64. 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 sys_base64? +

sys_base64 is provided by the Onion MCP server (onion-ai/mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.