Urgent Security Bulletin: CVE-2026-1904 — Authenticated (Contributor+) Stored XSS in Simple Wp colorfull Accordion (≤ 1.0) and How to Protect Your Site

Fecha: 2026-02-13
Autor: Experto en seguridad de Hong Kong

Nota: This advisory covers CVE-2026-1904 affecting Simple Wp colorfull Accordion versions ≤ 1.0. The issue is an authenticated (Contributor+) stored Cross-Site Scripting (XSS) via the shortcode título attribute. The write-up focuses on defensive controls, detection and practical mitigations for site owners and developers.

Tabla de contenido

• Resumen
• Who is affected and prerequisites
• Why this vulnerability matters (risk & impact)
• How the vulnerability works (high level, safe description)
• Escenarios de ataque realistas
• Detecting if your site is vulnerable or has been exploited
• Mitigaciones inmediatas para propietarios de sitios (paso a paso)
• Web Application Firewall (WAF) guidance
• Developer guidance: how to fix plugin code correctly
• Remediation, verification and clean-up
• Long-term hardening best practices
• If you are already compromised: incident response checklist
• Practical safe examples and commands (admin & developer)
• Notas de cierre

Resumen

A stored Cross-Site Scripting (XSS) vulnerability was disclosed in the Simple Wp colorfull Accordion plugin (affecting versions ≤ 1.0), tracked as CVE-2026-1904. An authenticated user with Contributor privileges (or higher) can inject unsanitized content via the plugin’s shortcode título attribute. When that content is rendered on public pages it can execute in visitors’ browsers.

This is an authenticated stored XSS with a practical impact: the attacker needs contributor-level access to inject payloads, but the payload executes in the context of anyone viewing the page. Consequences include session theft, content defacement, unwanted redirects, or enabling follow-on actions.

This advisory explains the issue safely, how to detect it, and defensive mitigations you can apply immediately without waiting for an upstream plugin fix.

Who is affected and prerequisites

• Affected plugin: Simple Wp colorfull Accordion
• Versiones vulnerables: ≤ 1.0
• Privilege required: Contributor role or higher (authenticated)
• Type: Stored Cross-Site Scripting (XSS) via título shortcode attribute
• CVE: CVE-2026-1904
• Patch status: Treat the plugin as vulnerable until an official fixed release is available

Contributor accounts are common on multi-author blogs, membership sites, LMS platforms and other sites that accept third-party content. If your site allows registration and assigns Contributor (or higher) roles to untrusted users, consider this an operational risk that requires immediate attention.

Why this vulnerability matters (risk & impact)

Stored XSS enables an attacker to execute arbitrary JavaScript in the browser of a visitor who views an infected page. Even though an attacker needs contributor access to inject content, the downstream impacts can be significant:

• Compromiso del visitante: Any visitor of the infected page may have scripts executed in their browser.
• Session theft & account takeover: If an authenticated administrator views the infected content, cookies or session tokens can be stolen or forged requests made to escalate privileges.
• Daño a la reputación y SEO: Malicious redirects, phishing forms, or injected spam can result in search blacklisting and customer trust loss.
• Persistent follow-on attacks: Attackers can plant further payloads or manipulate client-side actions to create backdoors.

The CVSS for this issue was reported as 6.5 (medium), reflecting the required privileges and the need for a victim to view the payload. Sites with multiple contributors or open registrations are at higher risk.

How the vulnerability works (high level, safe description)

WordPress shortcodes are replaced with HTML when content is rendered. The vulnerable plugin accepts a título attribute and outputs it into the page markup without sufficient sanitization or escaping.

1. An authenticated user with Contributor privileges publishes or updates a post that contains the plugin’s shortcode and sets título to a crafted value.
2. The plugin renders the título directly into HTML on page view.
3. Because the value is not properly escaped or filtered, a malicious script in título may run in the browser of anyone who views the page.

This is classic stored XSS: input is stored in post content and later output unsafely.

Escenarios de ataque realistas

1. Rogue contributor: A contributor creates or edits a post, inserts the shortcode with a malicious título, and publishes it. The payload is persistent and affects visitors.
2. Cuenta de colaborador comprometida: If credentials for a contributor are compromised (weak or reused passwords), the attacker can inject payloads aimed at administrators or editors who view pages while logged in.
3. Targeting subscribers: An infected page linked from newsletters or social media can deliver malicious redirects or phishing content to readers.
4. Encadenando vulnerabilidades: The XSS can be used to fingerprint admin endpoints or perform privileged actions if other protections are weak.

Detecting if your site is vulnerable or has been exploited

Detection requires two tracks: confirm the vulnerable plugin/version is present, and search for signs of injected payloads in posts, pages and the database.

1. Confirme el plugin y la versión: In WP admin, check Plugins → Installed Plugins for Simple Wp colorfull Accordion and verify the version. If ≤ 1.0, assume vulnerability.
2. Search post content for the shortcode: Use WP admin search or WP-CLI to locate posts/pages using the shortcode.

# Example WP-CLI approach (adjust shortcode name if necessary)
wp post list --post_type=post,page --format=ids | xargs -n1 -I{} wp post get {} --field=content | grep -n "simple_wp_colorfull_accordion"

3. Inspeccionar título attributes: Busque <script> etiquetas, controladores de eventos (por ejemplo,. onerror=, onload=), javascript: URIs, or encoded payloads like %3Cscript%3E.
4. Front-end HTML inspection: View page source on pages that include the shortcode and check for inline scripts or suspicious attributes.
5. Revisar registros: Review webserver access logs for POSTs to wp-admin/post.php, wp-admin/post-new.php or REST endpoints containing suspicious content. If you have logging/alerting, search for unusual POST bodies.
6. User reports: Pay attention to reports of unexpected redirects, popups or odd page behavior from visitors or staff.

Mitigaciones inmediatas para propietarios de sitios (paso a paso)

Prioritise actions that are fast, reversible and minimise business impact.

1. Quarantine the plugin: If the plugin is active and you cannot immediately verify content is clean, deactivate it: Plugins → Installed Plugins → Simple Wp colorfull Accordion → Deactivate. This prevents shortcode rendering on the front end.
2. Restrict Contributor posting temporarily: Remove or reduce posting privileges for Contributors, disable auto-publishing by low-privilege users, or require editorial review while you triage.
3. Search & sanitize existing content: Find posts/pages with the shortcode and inspect título attributes. Remove or sanitize untrusted values. WP-CLI can help with safe batch operations:

# List posts containing the shortcode (example)
wp post list --post_type=post,page --format=ids | \
xargs -n1 -I{} sh -c 'wp post get {} --field=post_content | grep -q "simple_wp_colorfull_accordion" && echo {}'

4. Temporary output sanitization: If you cannot deactivate the plugin, add a mu-plugin filter that sanitises título at render time. Example (temporary mitigation):

// mu-plugins/sanitize-accordion-title.php
add_filter('the_content', function($content) {
    $content = preg_replace_callback(
       '/(\[simple_wp_colorfull_accordion[^\]]*title=)(["\'])(.*?)\2/i',
       function($m){
           $clean = wp_strip_all_tags( $m[3] );
           $clean = esc_attr( $clean );
           return $m[1] . $m[2] . $clean . $m[2];
       },
       $content
    );
    return $content;
}, 999);

Note: This is a short-term fix to neutralise script content; it should be removed once a proper upstream patch and content clean-up are complete.

5. Remove or reset affected user accounts: Suspend or reset passwords for untrusted contributor accounts while investigating.
6. Escanea el sitio: Run a full malware and integrity scan for suspicious files, modified core files, and unexpected plugins.
7. Copia de seguridad: Create a full backup (files + DB) before making changes and retain copies for forensic purposes.
8. Apply request-level filters: Block or challenge admin POSTs containing obvious script tags or event handlers in shortcode attributes (see WAF guidance below).
9. Monitorea: Keep heightened monitoring for at least 30 days — attackers often return after initial disclosures.

Web Application Firewall (WAF) guidance

If you operate a WAF (managed or self-hosted), use it to reduce immediate risk. Do not rely on this as a permanent substitute for code fixes, but it can buy time while you clean and patch.

• Request inspection for post submissions: Block or challenge POSTs to wp-admin/post.php, REST endpoints (/wp-json/wp/v2/posts) o xmlrpc.php that include shortcode attributes containing script tags, event handlers or javascript: URIs.
• Detection regex (tune before use):

(?i)\[simple_wp_colorfull_accordion[^\]]*title\s*=\s*(['"]).*?(?:<\s*script\b|on\w+\s*=|javascript:).*?\1

• Output inspection: If possible, inspect HTML responses for inline script fragments inside accordion titles and either sanitize or block the response.
• Limitación de tasa: Apply rate limits or behavioural controls for new or low-reputation contributors to reduce abuse.
• Logging & alerts: Enable alerts for blocked or suspicious events to provide visibility into exploitation attempts.
• Deployment advice: Deploy detection rules in log-only mode first to tune false positives, then move to blocking once tuned.

Developer guidance: how to fix plugin code correctly

If you maintain the plugin or a theme that outputs shortcodes, apply secure coding practices: sanitize inputs, validate attributes, and escape on output.

1. Sanitize attributes at parse time:

   $atts = shortcode_atts( array(
       'title' => '',
       // other attrs...
   ), $atts, 'simple_wp_colorfull_accordion' );
   
   $title = isset( $atts['title'] ) ? sanitize_text_field( $atts['title'] ) : '';
   

2. Escapa en la salida:

   echo '<div class="accordion" data-title="' . esc_attr( $title ) . '">';'<h3>' . esc_html( $title ) . '</h3>';
   

3. If HTML is required, use a strict whitelist:

   $allowed = array(
       'strong' => array(),
       'em' => array(),
       'span' => array('class' => array()),
   );
   $title = wp_kses( $atts['title'], $allowed );
   

4. Avoid storing unsanitized content: Sanitize before saving to post meta or transients.
5. Comprobaciones de capacidad y nonces: Proteger los puntos finales de administración:

   if ( ! current_user_can( 'edit_posts' ) ) {
       wp_die( 'Unauthorized' );
   }
   check_admin_referer( 'my_plugin_nonce_action', 'my_plugin_nonce_field' );
   

6. Pruebas automatizadas: Add unit and security tests to ensure attributes containing scripts are properly cleansed.

Remediation, verification and clean-up

1. Actualiza el plugin: When an official patched version is released, update via WordPress updates or apply the patch manually.
2. Re-scan for injected content: Re-inspect posts and pages for malicious payloads and sanitise or remove any found.
3. Re-enable functionality carefully: Remove temporary filters or re-activate the plugin only after confirming content is clean.
4. Rotar credenciales: If account compromise is suspected, rotate passwords and enforce stronger authentication (2FA) for privileged users.
5. Monitor post-fix activity: Watch logs for attempts to re-exploit or re-inject payloads after patching.
6. Backup hygiene: Maintain immutable backups from before and after remediation for rollback and forensics.

Long-term hardening best practices

• Menor privilegio: Grant users the minimum capabilities required. Employ editorial workflows where possible.
• MFA: Enforce multi-factor authentication for users with publishing rights.
• Use a WAF: Consider a properly tuned WAF for virtual patching of critical issues while you apply fixes.
• Encabezados de seguridad: Implement Content-Security-Policy (CSP), X-Content-Type-Options, X-Frame-Options and Referrer-Policy to reduce XSS impact.
• Higiene del plugin: Remove unused plugins and prefer actively maintained plugins with recent updates.
• Monitoreo de vulnerabilidades: Subscribe to CVE notifications and monitor plugin ecosystems for disclosures.
• Logging & SIEM: Centralise logs and create alerts for anomalous admin POSTs and suspicious shortcode content.
• Contributor education: Train content creators on safe content practices and limit HTML support for low-privilege roles.

If you are already compromised: incident response checklist

1. Aislar: Take the site offline (maintenance mode) to limit harm to visitors.
2. Preservar evidencia: Make a forensic snapshot (DB + files) and store it securely.
3. Inventory affected pages: Identify pages containing the vulnerable shortcode and mark them suspect.
4. Remove malicious content and backdoors: Clean infected posts and search for rogue admin users, cron jobs, suspicious plugins, and modified core files.
5. Fuerce restablecimientos de contraseña: Reset passwords for all users with publishing or admin privileges and enforce 2FA.
6. put the site into maintenance mode or take it temporarily offline. For severe compromises, rebuild from a known-good backup and reinstall plugins/themes from official sources.
7. Revisión posterior al incidente: Realiza un análisis de causa raíz y refuerza los controles para prevenir recurrencias.

If you require professional assistance with cleanup or forensic investigation, engage a reputable security consultant experienced with WordPress incident response.

Practical safe examples and commands (admin & developer)

• Search posts for the shortcode (WP-CLI):

  wp db query "SELECT ID, post_title FROM wp_posts WHERE post_content LIKE '%simple_wp_colorfull_accordion%';"
  

• Sanitize a suspicious título attribute: Edit the post in WP Admin, switch to code editor, locate the shortcode and remove or replace the título attribute with safe text.
• Quick filter to disable shortcode rendering (temporary):

  // mu-plugins/disable-accordion-shortcode.php
  add_action('init', function() {
      remove_shortcode('simple_wp_colorfull_accordion');
  });
  

  Note: Removing the shortcode stops rendering but leaves raw shortcode text visible; use only as an emergency step while sanitising content.

• Safe escaping example for plugin developers:

  // Safe output of title attribute
  $title_raw = isset( $atts['title'] ) ? sanitize_text_field( $atts['title'] ) : '';
  echo '<div class="accordion" data-title="' . esc_attr( $title_raw ) . '">';
  

Notas de cierre

Authenticated stored XSS issues such as CVE-2026-1904 demonstrate why layered defence is essential:

• Plugin authors must sanitise and escape correctly.
• Site owners must enforce least privilege and monitor user activity.
• WAFs and request filters can provide temporary virtual patches while code fixes and content clean-up are performed.

If you operate sites that accept third-party content or have open user workflows, review contributor permissions, inspect pages that use the affected plugin, and apply the temporary mitigations described above immediately.

Stay vigilant. If you need hands-on help, contact a qualified WordPress security consultant or your internal security team.

— Experto en Seguridad de Hong Kong