fix(permissions): ignore unknown permission values

The permission checks did not check for unknown permission values
submitted to the server. This allowed bypassing permission checks
under certain circumstances. However, this is not as critical as
it might sound at first, since checks guard that only the owner
can modify note permissions and the owner already has always
full permission to their note.

Signed-off-by: Erik Michelson <github@erik.michelson.eu>

lib/realtime.js

@@ -29,6 +29,8 @@ const realtime = {
   maintenance: true
 }
 
+const allowedPermissionValues = ['freely', 'editable', 'limited', 'locked', 'protected', 'private']
+
 function onAuthorizeSuccess (data, accept) {
   accept()
 }
@@ -363,13 +365,25 @@ function connectNextSocket () {
 }
 
 function checkViewPermission (req, note) {
-  if (note.permission === 'private') {
-    if (req.user && req.user.logged_in && req.user.id === note.owner) { return true } else { return false }
-  } else if (note.permission === 'limited' || note.permission === 'protected') {
-    if (req.user && req.user.logged_in) { return true } else { return false }
-  } else {
+  const permission = note.permission
+
+  // Private notes should only be readable to their owner
+  if (permission === 'private') {
+    return req.user && req.user.logged_in && req.user.id === note.owner
+  }
+
+  // Limited and protected notes should be readable by all logged-in users
+  if (permission === 'limited' || permission === 'protected') {
+    return req.user && req.user.logged_in
+  }
+
+  // Freely, Editable and Locked notes should be readable by everyone
+  if (permission === 'freely' || permission === 'editable' || permission === 'locked') {
     return true
   }
+
+  // Invalid permission
+  return false
 }
 
 let isConnectionBusy = false
@@ -636,6 +650,10 @@ function ifMayEdit (socket, callback) {
       // only owner can change
       if (!note.owner || note.owner !== socket.request.user.id) { mayEdit = false }
       break
+    default:
+      // invalid permission
+      mayEdit = false
+      break
   }
   // if user may edit and this is a text operation
   if (socket.origin === 'operation' && mayEdit) {
@@ -778,7 +796,14 @@ function connection (socket) {
       const note = notes[noteId]
       // Only owner can change permission
       if (note.owner && note.owner === socket.request.user.id) {
-        if (permission === 'freely' && !config.allowAnonymous && !config.allowAnonymousEdits) return
+        // If config disallows freely permission, do not set it
+        if (permission === 'freely' && !config.allowAnonymous && !config.allowAnonymousEdits) {
+          return
+        }
+        // Ignore invalid permission values
+        if (!allowedPermissionValues.includes(permission)) {
+          return
+        }
         note.permission = permission
         models.Note.update({
           permission

public/docs/release-notes.md

@@ -2,6 +2,10 @@
 
 ## <i class="fa fa-tag"></i> 1.11.1 <i class="fa fa-calendar-o"></i> 2026-07-24
 
+### Security fixes
+
+- [GHSA-93w7-49m2-cqwg](https://github.com/hedgedoc/hedgedoc/security/advisories/GHSA-93w7-49m2-cqwg) reports possible corruption of permission values due to missing validation. This should not impact permission checks, except when the note owner intentionally set their note permission to something invalid.
+
 ### Enhancements
 
 - Added external link warning setting (`externalLinkWarning` in config.json or `CMD_EXTERNAL_LINK_WARNING`) to disable the external link warning page entirely