Rocket.Chat/server/startup/migrations/v064.js

import s from 'underscore.string';

RocketChat.Migrations.add({
	version: 64,
	up() {
		RocketChat.models.Messages.find({ t: 'room_changed_topic', msg: /</ }, { msg: 1 }).forEach(function(message) {
			const msg = s.escapeHTML(message.msg);
			RocketChat.models.Messages.update({ _id: message._id }, { $set: { msg } });
		});
	},
});