Message ID Enumeration with Action Link Handler

Summary

Summary

The actionLinkHandler method was found to allow Message ID Enumeration with Regex MongoDB queries.

Releases Affected:

The Meteor method actionLinkHandler calls an actionLinks wrapper getMessage to find affected messages:

Meteor.methods({
	actionLinkHandler(name, messageId) {
		if (!Meteor.userId()) {
			throw new Meteor.Error('error-invalid-user', 'Invalid user', { method: 'actionLinkHandler' });
		}

		const message = actionLinks.getMessage(name, messageId);
		const actionLink = message.actionLinks[name];

		actionLinks.actions[actionLink.method_id](message, actionLink.params);
	},
});

The actionLinks.getMessage method does not validate the input data, so that a { $regex: ".*" } pattern can be used to enumerate for the existence of Messages with MongoDB Injection.

getMessage(name, messageId) {
	const userId = Meteor.userId();
	if (!userId) {
		throw new Meteor.Error('error-invalid-user', 'Invalid user', { function: 'actionLinks.getMessage' });
	}

	const message = Messages.findOne({ _id: messageId });
	if (!message) {
		throw new Meteor.Error('error-invalid-message', 'Invalid message', { function: 'actionLinks.getMessage' });
	}
	// ...
}

Whenever a Message ID does not match any existing message, the server will respond with invalid-message error. When it does exist, a different response (or error) is returned, so that the guess can be evaluated.

Meteor.call(
  "actionLinkHandler",
  "joinJitsiCall",
  { $regex: ".*" },
  console.log
);

Although only Message IDs (and not their content) can be enumerated, mitigating this issue becomes relevant to prevent adversaries from stacking it with other information disclosure vulnerabilities that would leak a message content for known Message IDs.

Steps To Reproduce (from initial installation to vulnerability):

1. Login to Rocket.Chat
2. Query actionLinkHelper to check if a message matches
3. Extend static part of the regex
4. Repeat step 2

Suggested mitigation

• Check messageId for String type

Impact

Authenticated adversaries can enumerate the server for existing Message IDs.

Fix

Fixed in 4.7.5, 4.8.2 and 5.0>