set_custom_property

THE RISK

Medium Risk

Why set_custom_property needs a policy

This tool creates or modifies document metadata (custom properties) in a reversible manner. It does not execute code, trigger external operations, delete data irreversibly, or move financial resources. The impact is confined to updating document metadata, which can be undone.

From the tool's definition Tool name is 'set_custom_property' with description 'Set (upsert) a custom document property.' The term 'set (upsert)' explicitly indicates creation or modification of data.

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

POLICY

How to control set_custom_property

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

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "set_custom_property": {
      "limits": [
        {
          "counter": "set_custom_property_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

set_custom_property 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.

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

LIMIT THIS TOOL →

Free to start. No card required.

EXPLORE

Related tools and policies

More Docx tools

Destructive delete_column_from_table Delete a column (0-based) from every row of a table. Destructive delete_comment Delete a comment and remove its range markers from the document. Destructive delete_content_control Remove an SDT content control wrapper, keeping its content in place. Destructive delete_custom_property Delete a custom document property by name. Destructive delete_endnote Delete an endnote and its in-body reference. Destructive delete_field Remove a complete complex field (begin through end runs) from the document. Destructive delete_footer Delete a footer by location: default, first, or even. Destructive delete_footnote Delete a footnote and its in-body reference.

All 219 Docx tools →

Write tools on other servers

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Go deeper

The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Argument validation → Checking tool call arguments against schema and policy before they run.
Scoped token → Per-person credentials that grant a defined subset of servers and tools.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about set_custom_property

What does the set_custom_property tool do? +

Set (upsert) a custom document property. It is categorised as a Write tool in the Docx MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on set_custom_property? +

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

What risk level is set_custom_property? +

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

Can I rate-limit set_custom_property? +

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

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

set_custom_property is provided by the Docx MCP server (securityronin/docx-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Docx tool call.

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

CHECK YOUR STACK →