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<title>[41741] trunk/src/wp-admin/includes: Security: Add a referrer policy header to the admin and login screens.</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/41741">41741</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/41741","name":"Review Commit"}}</script></dd>
<dt style="float: left; width: 6em; font-weight: bold">Author</dt> <dd>johnbillion</dd>
<dt style="float: left; width: 6em; font-weight: bold">Date</dt> <dd>2017-10-04 18:24:17 +0000 (Wed, 04 Oct 2017)</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'>Security: Add a referrer policy header to the admin and login screens.
This sets a referrer policy of `same-origin` which adds hardening by preventing a referrer being sent from the admin area or login screens to other origins. This helps prevent unwanted exposure of potentially sensitive information that may be contained within URLs.
This change introduces a new filter, `admin_referrer_policy`, for filtering the referrer policy header value. The header can be disabled if necessary by removing the `wp_admin_headers` action from the `admin_init` and `login_init` hooks.
Props joostdevalk
Fixes <a href="https://core.trac.wordpress.org/ticket/42036">#42036</a></pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunksrcwpadminincludesadminfiltersphp">trunk/src/wp-admin/includes/admin-filters.php</a></li>
<li><a href="#trunksrcwpadminincludesmiscphp">trunk/src/wp-admin/includes/misc.php</a></li>
</ul>
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<h3>Diff</h3>
<a id="trunksrcwpadminincludesadminfiltersphp"></a>
<div class="modfile"><h4 style="background-color: #eee; color: inherit; margin: 1em 0; padding: 1.3em; font-size: 115%">Modified: trunk/src/wp-admin/includes/admin-filters.php</h4>
<pre class="diff"><span>
<span class="info" style="display: block; padding: 0 10px; color: #888">--- trunk/src/wp-admin/includes/admin-filters.php 2017-10-04 18:11:08 UTC (rev 41740)
+++ trunk/src/wp-admin/includes/admin-filters.php 2017-10-04 18:24:17 UTC (rev 41741)
</span><span class="lines" style="display: block; padding: 0 10px; color: #888">@@ -38,6 +38,8 @@
</span><span class="cx" style="display: block; padding: 0 10px"> add_filter( 'media_upload_tabs', 'update_gallery_tab' );
</span><span class="cx" style="display: block; padding: 0 10px">
</span><span class="cx" style="display: block; padding: 0 10px"> // Misc hooks.
</span><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+add_action( 'admin_init', 'wp_admin_headers' );
+add_action( 'login_init', 'wp_admin_headers' );
</ins><span class="cx" style="display: block; padding: 0 10px"> add_action( 'admin_head', 'wp_admin_canonical_url' );
</span><span class="cx" style="display: block; padding: 0 10px"> add_action( 'admin_head', 'wp_color_scheme_settings' );
</span><span class="cx" style="display: block; padding: 0 10px"> add_action( 'admin_head', 'wp_site_icon' );
</span></span></pre></div>
<a id="trunksrcwpadminincludesmiscphp"></a>
<div class="modfile"><h4 style="background-color: #eee; color: inherit; margin: 1em 0; padding: 1.3em; font-size: 115%">Modified: trunk/src/wp-admin/includes/misc.php</h4>
<pre class="diff"><span>
<span class="info" style="display: block; padding: 0 10px; color: #888">--- trunk/src/wp-admin/includes/misc.php 2017-10-04 18:11:08 UTC (rev 41740)
+++ trunk/src/wp-admin/includes/misc.php 2017-10-04 18:24:17 UTC (rev 41741)
</span><span class="lines" style="display: block; padding: 0 10px; color: #888">@@ -920,6 +920,27 @@
</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"> /**
</span><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ * Send a referrer policy header so referrers are not sent externally from administration screens.
+ *
+ * @since 4.9.0
+ */
+function wp_admin_headers() {
+ $policy = 'same-origin';
+
+ /**
+ * Filters the admin referrer policy header value. Default 'same-origin'.
+ *
+ * @since 4.9.0
+ * @link https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Referrer-Policy
+ *
+ * @param string $policy The referrer policy header value.
+ */
+ $policy = apply_filters( 'admin_referrer_policy', $policy );
+
+ header( sprintf( 'Referrer-Policy: %s', $policy ) );
+}
+
+/**
</ins><span class="cx" style="display: block; padding: 0 10px"> * Outputs JS that reloads the page if the user navigated to it with the Back or Forward button.
</span><span class="cx" style="display: block; padding: 0 10px"> *
</span><span class="cx" style="display: block; padding: 0 10px"> * Used on the Edit Post and Add New Post screens. Needed to ensure the page is not loaded from browser cache,
</span></span></pre>
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