Viewer users can publish documents into restricted collections through Outline MCP workflow

Summary

A broken access control vulnerability exists in Outline’s MCP workflow which allows users with viewer permissions to publish documents into restricted collections.

Although the user is correctly identified as read-only, the MCP workflow still allows draft creation and subsequent publication into collections where the user should not have write access.

Details

I tested this issue on an Outline workspace with MCP enabled.

Using a user account with only viewer permissions, I connected the official Outline MCP server URL to Claude Desktop.

I then instructed Claude to create a new document.

Initially, Claude correctly responded that my account did not have permission to create documents because the account only had viewer access. However, while reviewing the Outline application, I noticed that a draft document had been created successfully in the backend.

The created draft document was associated with my low-privileged viewer account.

After observing this behavior, I instructed Claude to publish the document into a restricted collection where the viewer account did not have document creation or publishing permissions.

The document was successfully published into the restricted collection.

This suggests that the MCP workflow are not consistently enforcing RBAC permissions during draft creation and publication flows.

PoC

Video demonstration:
https://youtu.be/UyZwcvfiA-Y

Preconditions

• Outline workspace with MCP enabled
• User account with viewe…