update_ref · Substrate MCP: Risk & Policy

WHAT IT DOES

What update_ref does on Substrate

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

WHY IT NEEDS A POLICY

Why update_ref needs a policy

The tool updates (modifies) existing references, which is a Write operation. It is not Destructive because updates are typically reversible (the old value is replaced but not permanently lost in most reference systems). Severity is medium because unintended updates to references could break system functionality or configurations, but the impact is typically recoverable through subsequent updates or rollbacks.

From the tool's definition Tool name 'update_ref' and description 'Update existing reference' indicate modification of existing data in a reversible manner.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

update_ref Rate-limited

update_ref 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": {
    "update_ref": {
      "limits": [
        {
          "counter": "update_ref_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 Substrate, so you can run agents against it safely.

FAQ

Questions about update_ref

What does the update_ref tool do? +

Update existing reference. It is categorised as a Write tool in the Substrate MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on update_ref? +

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

What risk level is update_ref? +

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

Can I rate-limit update_ref? +

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

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

update_ref is provided by the Substrate MCP server (ivan-saorin/substrate). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.