deserialize_object · Vulnerable MCP Server MCP

WHAT IT DOES

What deserialize_object does on Vulnerable MCP Server

AI agents invoke deserialize_object to trigger actions in Vulnerable MCP Server. 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 deserialize_object needs a policy

Python's pickle module allows arbitrary code execution during deserialization. An attacker (or misused AI agent) can craft a malicious pickle payload that runs any system command or code when deserialized.

From the tool's definition Deserialize a base64-encoded Python pickle object — Python pickle deserialization is a well-known arbitrary code execution vector; combined with a server explicitly described as 'deliberately insecure' and a pentest lab context, this tool can execute…

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

deserialize_object Rate-limited

deserialize_object 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": {
    "deserialize_object": {
      "limits": [
        {
          "counter": "deserialize_object_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 Vulnerable MCP Server, so you can run agents against it safely.

FAQ

Questions about deserialize_object

What does the deserialize_object tool do? +

Deserialize a base64-encoded Python pickle object for data transfer between services. It is categorised as a Execute tool in the Vulnerable MCP Server MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on deserialize_object? +

Register the Vulnerable MCP Server MCP server in PolicyLayer and add a rule for deserialize_object: 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 Vulnerable MCP Server. Nothing to install.

What risk level is deserialize_object? +

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

Can I rate-limit deserialize_object? +

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

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

deserialize_object is provided by the Vulnerable MCP Server MCP server (joyghoshs/vulnerable-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.