canvases_access_set · Slack MCP: Risk & Policy

WHAT IT DOES

What canvases_access_set does on Slack

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

WHY IT NEEDS A POLICY

Why canvases_access_set needs a policy

This tool modifies access permissions on Slack canvases, which is a reversible Write operation affecting data governance and user permissions. It does not create/delete canvases themselves (which would be separate operations), but reconfigures who can access them.

From the tool's definition Tool name 'canvases_access_set' indicates modification of access controls on Slack canvases. The 'set' verb suggests updating/changing permissions or access settings.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

canvases_access_set Rate-limited

canvases_access_set 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": {
    "canvases_access_set": {
      "limits": [
        {
          "counter": "canvases_access_set_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 Slack, so you can run agents against it safely.

FAQ

Questions about canvases_access_set

What does the canvases_access_set tool do? +

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

How do I enforce a policy on canvases_access_set? +

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

What risk level is canvases_access_set? +

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

Can I rate-limit canvases_access_set? +

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

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

canvases_access_set is provided by the Slack MCP server (karbassi/slack-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.