fix: even stricter sanitization rules by default

- id, rel, target attributes may also not occur in plaintext or markdown formatted documents (source code tolerates no HTML at all) or comments
- urls2links is the only part in that call stack that is allowed to add anchors (a-tags with href-attribute), then sanitizes as strict as possible, then adds rel & target attributes of it's own
- we also use a afterSanitizeAttributes-hook into any DOMpurify call that replaces or sets rel & target attributes on all links (this duplicates the extra logic in urls2links)
- finally we add a slightly less strict config for only the translation strings with the known tags and including the id attribute, which is used in at least one translation message

js/privatebin.js

@@ -56,7 +56,7 @@ window.PrivateBin = (function () {
      */
     const purifyHtmlConfig = {
         ALLOWED_URI_REGEXP: /^(?:(?:(?:f|ht)tps?|mailto|magnet):)/i,
-        ALLOWED_ATTR: ['href', 'id', 'target', 'rel'],
+        ALLOWED_ATTR: ['href'],
         USE_PROFILES: {
             html: true
         }
@@ -72,9 +72,8 @@ window.PrivateBin = (function () {
      */
     const purifyHtmlConfigStrictSubset = {
         ALLOWED_URI_REGEXP: purifyHtmlConfig.ALLOWED_URI_REGEXP,
-        ALLOWED_TAGS: ['a', 'i', 'span', 'kbd'],
-        ALLOWED_ATTR: ['href', 'id', 'target', 'rel'],
-        ADD_ATTR: ['target', 'rel']
+        ALLOWED_TAGS: ['a'],
+        ALLOWED_ATTR: ['href']
     };
 
     /**
@@ -89,6 +88,20 @@ window.PrivateBin = (function () {
         }
     };
 
+    /**
+     * DOMpurify settings for translated messages, which are allowed to include limited HTML.
+     *
+     * NOTE: The key {@link purifyHtmlConfig.USE_PROFILES} **must not** be included,
+     * as otherwise `USE_PROFILES` takes precedence over {@link purifyHtmlConfigStrictSubset.ALLOWED_TAGS}.
+     *
+     * @private
+     */
+    const purifyTranslationConfig = {
+        ALLOWED_URI_REGEXP: /^(?:https?:)/i, // the only URL expected here is the generated document, so only http & https
+        ALLOWED_TAGS: ['a', 'i', 'span', 'kbd'],
+        ALLOWED_ATTR: ['href', 'id'] // one of the messages contains an id attribute
+    };
+
     /**
      * URL fragment prefix requiring load confirmation
      *
@@ -805,7 +818,7 @@ window.PrivateBin = (function () {
 
             if (containsHtml) {
                 // only allow tags/attributes we actually use in translations
-                output = DOMPurify.sanitize(output, purifyHtmlConfigStrictSubset);
+                output = DOMPurify.sanitize(output, purifyTranslationConfig);
             }
 
             // if element is given, insert translation

lib/Configuration.php

@@ -124,7 +124,7 @@ class Configuration
             'js/kjua-0.10.0.js'      => 'sha512-BYj4xggowR7QD150VLSTRlzH62YPfhpIM+b/1EUEr7RQpdWAGKulxWnOvjFx1FUlba4m6ihpNYuQab51H6XlYg==',
             'js/legacy.js'           => 'sha512-pRofxsrf5UItjiP22Dcjh3FAcBjF/n7h8U9/W5xqJk17U0N2U1oajhXypq/omo9jhwS1iVGOhWrRepoPeFns+w==',
             'js/prettify.js'         => 'sha512-puO0Ogy++IoA2Pb9IjSxV1n4+kQkKXYAEUtVzfZpQepyDPyXk8hokiYDS7ybMogYlyyEIwMLpZqVhCkARQWLMg==',
-            'js/privatebin.js'       => 'sha512-WQWTb5leu1zfMFK19z+5wDU8Sqv0RxhYzeGP/4L5uu7lyRc7FtpL+S/kJMYyO266QPUMg4p52zRYDAMJgOFEwA==',
+            'js/privatebin.js'       => 'sha512-TESkKT3BI8chkAJUlFgIJxnBG/mtgHAKJk0sEMX3l554ohQvEyNjLl5ZFeVhT6jvW3mFIxengHfkc12+MokyJA==',
             'js/purify-3.4.12.js'    => 'sha512-Akf6HnAJZm0sWWWI4gp2GYff0NDnHUB02XJE5S7Hdq/Z5xtMjkuFacsDA8ZtViv1gi+onBxMhEMIaGyQeGxBng==',
             'js/showdown-2.1.0.js'   => 'sha512-WYXZgkTR0u/Y9SVIA4nTTOih0kXMEd8RRV6MLFdL6YU8ymhR528NLlYQt1nlJQbYz4EW+ZsS0fx1awhiQJme1Q==',
             'js/zlib-1.3.2.js'       => 'sha512-RAhJgxg9siMIA8ky4c10Rc2zUgnK80olHB8Tt1IOYWY4Eh1WmrviQkDn+sgBlb38ZHq3tzufGC41kP360gmosQ==',