security: New setting for Socket.IO `maxHttpBufferSize`

CHANGELOG.md

@@ -9,9 +9,10 @@
 * Dependencies are now installed with the `--no-optional` flag to speed
   installation. Optional dependencies such as `sqlite3` must now be manually
   installed (e.g., `(cd src && npm i sqlite3)`).
-* Socket.IO messages are now limited to 1MiB to make denial of service attacks
-  more difficult. This may cause issues with plugins that send large messages,
-  e.g., `ep_image_upload`.
+* Socket.IO messages are now limited to 10K bytes to make denial of service
+  attacks more difficult. This may cause issues when pasting large amounts of
+  text or with plugins that send large messages (e.g., `ep_image_upload`). You
+  can change the limit via `settings.json`; see `socketIo.maxHttpBufferSize`.
 * The top-level `package.json` file, added in v1.8.7, has been removed due to
   problematic npm behavior. Whenever you install a plugin you will see the
   following benign warnings that can be safely ignored:

settings.json.docker

@@ -445,6 +445,17 @@
    */
   "socketTransportProtocols" : ["xhr-polling", "jsonp-polling", "htmlfile"],
 
+  "socketIo": {
+    /*
+     * Maximum permitted client message size (in bytes). All messages from
+     * clients that are larger than this will be rejected. Large values make it
+     * possible to paste large amounts of text, and plugins may require a larger
+     * value to work properly, but increasing the value increases susceptibility
+     * to denial of service attacks (malicious clients can exhaust memory).
+     */
+    "maxHttpBufferSize": 10000
+  },
+
   /*
    * Allow Load Testing tools to hit the Etherpad Instance.
    *

settings.json.template

@@ -450,6 +450,17 @@
    */
   "socketTransportProtocols" : ["xhr-polling", "jsonp-polling", "htmlfile"],
 
+  "socketIo": {
+    /*
+     * Maximum permitted client message size (in bytes). All messages from
+     * clients that are larger than this will be rejected. Large values make it
+     * possible to paste large amounts of text, and plugins may require a larger
+     * value to work properly, but increasing the value increases susceptibility
+     * to denial of service attacks (malicious clients can exhaust memory).
+     */
+    "maxHttpBufferSize": 10000
+  },
+
   /*
    * Allow Load Testing tools to hit the Etherpad Instance.
    *

src/node/hooks/express/socketio.js

@@ -74,7 +74,7 @@ exports.expressCreateServer = (hookName, args, cb) => {
      *   https://github.com/socketio/socket.io/issues/2276#issuecomment-147184662 (not totally true, actually, see above)
      */
     cookie: false,
-    maxHttpBufferSize: 10E3,
+    maxHttpBufferSize: settings.socketIo.maxHttpBufferSize,
   });
 
   io.on('connect', (socket) => {

src/node/utils/Settings.js

@@ -104,6 +104,18 @@ exports.ssl = false;
  **/
 exports.socketTransportProtocols = ['xhr-polling', 'jsonp-polling', 'htmlfile'];
 
+exports.socketIo = {
+  /**
+   * Maximum permitted client message size (in bytes).
+   *
+   * All messages from clients that are larger than this will be rejected. Large values make it
+   * possible to paste large amounts of text, and plugins may require a larger value to work
+   * properly, but increasing the value increases susceptibility to denial of service attacks
+   * (malicious clients can exhaust memory).
+   */
+  maxHttpBufferSize: 10000,
+};
+
 /*
  * The Type of the database
  */