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<title>[60616] trunk: KSES: Prevent normalization from unescaping escaped numeric character references.</title>
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<dt style="float: left; width: 6em; font-weight: bold">Revision</dt> <dd><a style="font-weight: bold" href="https://core.trac.wordpress.org/changeset/60616">60616</a><script type="application/ld+json">{"@context":"http://schema.org","@type":"EmailMessage","description":"Review this Commit","action":{"@type":"ViewAction","url":"https://core.trac.wordpress.org/changeset/60616","name":"Review Commit"}}</script></dd>
<dt style="float: left; width: 6em; font-weight: bold">Author</dt> <dd>jonsurrell</dd>
<dt style="float: left; width: 6em; font-weight: bold">Date</dt> <dd>2025-08-07 07:58:33 +0000 (Thu, 07 Aug 2025)</dd>
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<pre style='padding-left: 1em; margin: 2em 0; border-left: 2px solid #ccc; line-height: 1.25; font-size: 105%; font-family: sans-serif'>KSES: Prevent normalization from unescaping escaped numeric character references.
Fixes an issue where `wp_kses_normalize_entities` would transform inputs like "&<a href="https://core.trac.wordpress.org/ticket/39">#39</a>;" into "&<a href="https://core.trac.wordpress.org/ticket/039">#039</a>;", changing the intended HTML text.
This behavior has present since the initial version of KSES was introduced in <a href="https://core.trac.wordpress.org/changeset/649">[649]</a>.
<a href="https://core.trac.wordpress.org/changeset/2896">[2896]</a> applied the normalization to post content for users without the "unfiltered_html" capability.
Developed in https://github.com/WordPress/wordpress-develop/pull/9099.
Props jonsurrell, dmsnell, sirlouen.
Fixes <a href="https://core.trac.wordpress.org/ticket/63630">#63630</a>.</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunksrcwpincludesksesphp">trunk/src/wp-includes/kses.php</a></li>
<li><a href="#trunktestsphpunittestsksesphp">trunk/tests/phpunit/tests/kses.php</a></li>
</ul>
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<h3>Diff</h3>
<a id="trunksrcwpincludesksesphp"></a>
<div class="modfile"><h4 style="background-color: #eee; color: inherit; margin: 1em 0; padding: 1.3em; font-size: 115%">Modified: trunk/src/wp-includes/kses.php</h4>
<pre class="diff"><span>
<span class="info" style="display: block; padding: 0 10px; color: #888">--- trunk/src/wp-includes/kses.php 2025-08-07 04:25:53 UTC (rev 60615)
+++ trunk/src/wp-includes/kses.php 2025-08-07 07:58:33 UTC (rev 60616)
</span><span class="lines" style="display: block; padding: 0 10px; color: #888">@@ -1958,14 +1958,45 @@
</span><span class="cx" style="display: block; padding: 0 10px"> // Disarm all entities by converting & to &
</span><span class="cx" style="display: block; padding: 0 10px"> $content = str_replace( '&', '&', $content );
</span><span class="cx" style="display: block; padding: 0 10px">
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">- // Change back the allowed entities in our list of allowed entities.
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ /*
+ * Decode any character references that are now double-encoded.
+ *
+ * It's important that the following normalizations happen in the correct order.
+ *
+ * At this point, all `&` have been transformed to `&`. Double-encoded named character
+ * references like `&amp;` will be decoded back to their single-encoded form `&`.
+ *
+ * First, numeric (decimal and hexadecimal) character references must be handled so that
+ * `&#09;` becomes `	`. If the named character references were handled first, there
+ * would be no way to know whether the double-encoded character reference had been produced
+ * in this function or was the original input.
+ *
+ * Consider the two examples, first with named entity decoding followed by numeric
+ * entity decoding. We'll use U+002E FULL STOP (.) in our example, this table follows the
+ * string processing from left to right:
+ *
+ * | Input | &-encoded | Named ref double-decoded | Numeric ref double-decoded |
+ * | ------------ | ---------------- | ------------------------- | -------------------------- |
+ * | `.` | `&#x2E;` | `&#x2E;` | `.` |
+ * | `&#x2E;` | `&amp;#x2E;` | `&#x2E;` | `.` |
+ *
+ * Notice in the example above that different inputs result in the same result. The second case
+ * was not normalized and produced HTML that is semantically different from the input.
+ *
+ * | Input | &-encoded | Numeric ref double-decoded | Named ref double-decoded |
+ * | ------------ | ---------------- | --------------------------- | ------------------------ |
+ * | `.` | `&#x2E;` | `.` | `.` |
+ * | `&#x2E;` | `&amp;#x2E;` | `&amp;#x2E;` | `&#x2E;` |
+ *
+ * Here, each input is normalized to an appropriate output.
+ */
+ $content = preg_replace_callback( '/&#(0*[0-9]{1,7});/', 'wp_kses_normalize_entities2', $content );
+ $content = preg_replace_callback( '/&#[Xx](0*[0-9A-Fa-f]{1,6});/', 'wp_kses_normalize_entities3', $content );
</ins><span class="cx" style="display: block; padding: 0 10px"> if ( 'xml' === $context ) {
</span><span class="cx" style="display: block; padding: 0 10px"> $content = preg_replace_callback( '/&([A-Za-z]{2,8}[0-9]{0,2});/', 'wp_kses_xml_named_entities', $content );
</span><span class="cx" style="display: block; padding: 0 10px"> } else {
</span><span class="cx" style="display: block; padding: 0 10px"> $content = preg_replace_callback( '/&([A-Za-z]{2,8}[0-9]{0,2});/', 'wp_kses_named_entities', $content );
</span><span class="cx" style="display: block; padding: 0 10px"> }
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">- $content = preg_replace_callback( '/&#(0*[0-9]{1,7});/', 'wp_kses_normalize_entities2', $content );
- $content = preg_replace_callback( '/&#[Xx](0*[0-9A-Fa-f]{1,6});/', 'wp_kses_normalize_entities3', $content );
</del><span class="cx" style="display: block; padding: 0 10px">
</span><span class="cx" style="display: block; padding: 0 10px"> return $content;
</span><span class="cx" style="display: block; padding: 0 10px"> }
</span></span></pre></div>
<a id="trunktestsphpunittestsksesphp"></a>
<div class="modfile"><h4 style="background-color: #eee; color: inherit; margin: 1em 0; padding: 1.3em; font-size: 115%">Modified: trunk/tests/phpunit/tests/kses.php</h4>
<pre class="diff"><span>
<span class="info" style="display: block; padding: 0 10px; color: #888">--- trunk/tests/phpunit/tests/kses.php 2025-08-07 04:25:53 UTC (rev 60615)
+++ trunk/tests/phpunit/tests/kses.php 2025-08-07 07:58:33 UTC (rev 60616)
</span><span class="lines" style="display: block; padding: 0 10px; color: #888">@@ -597,6 +597,12 @@
</span><span class="cx" style="display: block; padding: 0 10px"> 'Encoded named ref &amp;' => array( '&amp;', '&amp;' ),
</span><span class="cx" style="display: block; padding: 0 10px"> 'Encoded named ref &amp;' => array( '&amp;', '&amp;' ),
</span><span class="cx" style="display: block; padding: 0 10px"> 'Encoded named ref &amp;' => array( '&amp;', '&amp;' ),
</span><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ 'Encoded numeric ref &#39;' => array( '&#39;', '&#39;' ),
+ 'Encoded numeric ref &#39;' => array( '&#39;', '&#39;' ),
+ 'Encoded numeric ref &#39;' => array( '&#39;', '&#39;' ),
+ 'Encoded hex ref &#x27;' => array( '&#x27;', '&#x27;' ),
+ 'Encoded hex ref &#x27;' => array( '&#x27;', '&#x27;' ),
+ 'Encoded hex ref &#x27;' => array( '&#x27;', '&#x27;' ),
</ins><span class="cx" style="display: block; padding: 0 10px">
</span><span class="cx" style="display: block; padding: 0 10px"> /*
</span><span class="cx" style="display: block; padding: 0 10px"> * The codepoint value here is outside of the valid unicode range whose
</span><span class="lines" style="display: block; padding: 0 10px; color: #888">@@ -609,6 +615,7 @@
</span><span class="cx" style="display: block; padding: 0 10px">
</span><span class="cx" style="display: block; padding: 0 10px"> /**
</span><span class="cx" style="display: block; padding: 0 10px"> * @ticket 26290
</span><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ * @ticket 63630
</ins><span class="cx" style="display: block; padding: 0 10px"> *
</span><span class="cx" style="display: block; padding: 0 10px"> * @dataProvider data_normalize_entities
</span><span class="cx" style="display: block; padding: 0 10px"> */
</span></span></pre>
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