Résumé

A stored Cross-Site Scripting (XSS) vulnerability affecting the myCred WordPress plugin (versions ≤ 2.9.7.3) was disclosed and assigned CVE-2026-0550. An authenticated user with Contributor (or higher) privileges can inject a persistent malicious payload that is later rendered on the front end via the mycred_load_coupon shortcode. The issue is fixed in myCred 2.9.7.4. This advisory explains the technical risk, likely exploitation paths, detection strategies, and step-by-step remediation — including immediate hardening and virtual patching options.

If myCred is installed on any of your WordPress sites, read this fully and act now.

Faits rapides

• Affected plugin: myCred (WordPress)
• Vulnerable versions: ≤ 2.9.7.3
• Fixed version: 2.9.7.4
• Type de vulnérabilité : Script intersite stocké (XSS)
• Privilège requis pour exploiter : Contributeur (authentifié)
• CVE: CVE-2026-0550
• Estimated severity: Medium / CVSS 6.5 (authenticated user required, but persistent XSS)
• Exploitation impact: Attacker-supplied scripts executed in visitors’ browsers — possible account takeover, content injection, phishing, redirects, and client‑side exploits
• Immediate mitigation: Update the plugin; if immediate update is not possible, apply virtual patching via WAF rules and restrict contributor capabilities

Que s'est-il passé — en termes simples

myCred exposes a shortcode (mycred_load_coupon) that displays coupon content. In vulnerable versions, data that Contributors can create is not properly sanitized/escaped before being stored or output. A malicious Contributor could add markup or JavaScript into coupon fields that the shortcode later outputs unchanged into pages. Because the payload is stored in the database and rendered when visitors view the shortcode output, this is stored XSS — a persistent client-side vulnerability.

Stored XSS is particularly dangerous because the malicious content persists and can affect many visitors over time, including administrators and editors who view the affected page in the dashboard or front end.

Pourquoi cela vous concerne

1. Contributors are common: Many sites allow outside contributors, guest authors, affiliates, or low‑privileged users to create content. If you permit that role, your risk increases.
2. Stored XSS can affect trusted users: Admins and editors viewing the page could have cookies or session tokens exposed if an attacker crafts an exfiltration payload.
3. SEO and reputation damage: Malicious scripts can inject SEO spam, redirect visitors to malware/phishing pages, or display unwanted ads.
4. Lateral escalation: Attackers can use XSS to escalate privileges through session theft, CSRF, or social engineering of privileged users.

Exploitation scenario — what an attacker would do

• L'attaquant s'inscrit ou utilise un compte Contributeur existant.
• They create or edit a coupon and embed a payload (e.g., <script> balises, <img onerror="…">, or other event handlers).
• Le mycred_load_coupon shortcode is used on a public page; whenever a visitor or admin loads that page, the browser executes the injected script.
• Attacker can craft payloads to target admins or harvest visitor data at scale.

Exploitation requires at least Contributor access — a common role in many editorial workflows, so treat this as an urgent containment and clean-up item.

Confirmed fix and immediate action

• myCred released a patch: upgrade to version 2.9.7.4 (or later).
• If possible, update in staging first, then push to production.
• If you cannot update immediately (legacy sites, heavy customisations, blocked update windows), implement virtual patching via WAF and follow the containment steps below.

Step-by-step remediation checklist (practical, prioritized)

1. Update the plugin (highest priority)

• Update myCred to 2.9.7.4 or newer on all affected sites.
• If automatic updates are enabled, verify the plugin updated correctly.
• After update, confirm the affected pages no longer render injected content.

2. If you cannot update immediately — apply virtual patching (WAF)

• Deploy WAF rules that block requests attempting to submit <script> tags or suspicious event attributes (onerror, onclick, au chargement) within coupon creation/edit requests (admin POSTs).
• Block or neutralise content submissions containing common JavaScript payloads or encoded equivalents.
• Where feasible, strip/neutralise <script> et on*= attributes from server request payloads for endpoints that store coupon data.

3. Limit privileges and temporary policy changes

• Temporarily restrict who can create coupons or edit coupon content: remove that capability from the Contributor role or disable coupon creation UI for non‑trusted roles.
• Consider setting minimum role allowed to create/publish coupons to Editor/Administrator during the emergency window.
• Audit Contributor accounts and disable or reset passwords for unrecognised accounts.

4. Search for stored payloads and remove malicious artifacts

• Search the database for suspicious content (use WP-CLI or direct DB queries).
• Check coupon post types and plugin tables for suspicious HTML; remove or sanitize any findings.

5. Harden output escaping and sanitization (developer action)

• Ensure custom code using myCred shortcodes escapes output via WordPress functions: esc_html(), esc_attr(), wp_kses_post() où cela est approprié.
• If themes or child themes use raw myCred shortcode output, update them to sanitize values before output.

6. Enhance monitoring and logging

• Inspect recent admin activity logs for coupon creation/edit events by Contributors.
• Monitor WAF and web server logs for blocked attempts or suspicious POSTs with encoded payloads.
• Increase monitoring frequency for the next 14–30 days.

7. Incident response if you find evidence of exploitation

• Remove malicious content immediately.
• Invalidate sessions for all users and rotate admin credentials, especially if admins viewed affected pages.
• Review outbound logs for exfiltration attempts to attacker domains.
• Notify impacted users if credentials or sensitive data may have been exposed.
• Scan site files for secondary payloads or webshells; attackers sometimes leave backdoors.

8. Review and apply cookie security best practices

• Set authentication cookies to HttpOnly and SameSite where applicable.
• Use secure cookies (HTTPS only).
• Consider enforcing two‑factor authentication (2FA) for admin/editor accounts.

How to detect if you were targeted — practical checks

• Search for the mycred_load_coupon shortcode across your site and inspect outputs for unexpected HTML or script tags.
• Recherchez dans la base de données pour <script or event attributes (onload, onerror, onclick) in contenu_du_post, postmeta, and any custom myCred tables.
• Look for new or edited coupons after the disclosure date by Contributor accounts.
• Check admin action logs for coupon creation or edits by untrusted users.
• Review WAF and access logs for POST requests to coupon creation endpoints that look anomalous (base64 or URL encoded payloads, lots of special characters).
• Use a staging copy to render suspected pages and open browser DevTools to watch for network calls to unknown domains.

Example database queries (adjust table prefix if not wp_):

-- Find posts using the shortcode:
SELECT ID, post_title FROM wp_posts WHERE post_content LIKE '%mycred_load_coupon%';

-- Find postmeta or custom tables with script tags:
SELECT ID, post_title FROM wp_posts WHERE post_content REGEXP '<script[[:space:]]*[^>]*>';
SELECT meta_id, post_id, meta_value FROM wp_postmeta WHERE meta_value LIKE '%<script%';

-- If plugin stores coupons in a custom table, search that table for suspicious content.

Preventive hardening — policies to adopt immediately

• Principle of least privilege: review user roles monthly and remove capability creep from Contributors.
• Shortcode usage policy: avoid allowing contributors to insert privileged shortcodes that render raw HTML.
• Content filtering: apply server-side sanitization (e.g., wp_kses_post) for roles that can submit HTML.
• Continuous updates: keep plugins and themes updated; maintain a staging environment for testing upgrades.
• Data validation: developers must sanitize on input and escape on output.
• Content Security Policy (CSP): implement a restrictive CSP to limit inline script execution and external network calls.
• Security scans: run scheduled malware and vulnerability scans for your sites and installed plugins.
• Backups: maintain regular offsite backups and test restores before applying changes.

Recommended code hygiene for developers

If your code interacts with myCred outputs or renders shortcodes directly, ensure you:

• Escape before output:
  • Utilisez esc_html() for plain text output.
  • Utilisez esc_attr() pour les attributs.
  • Utilisez wp_kses_post() for sanitized HTML with an allowed tag set.
• Validate input: on save, remove disallowed tags with wp_kses() or use sanitize_text_field() if only text is expected.
• Éviter eval() or untrusted eval paths.
• Use nonces and capability checks for all admin POST endpoints.

Illustrative examples

<?php
// Assume $coupon_description is loaded from DB.
echo wp_kses_post( $coupon_description ); // Allows limited safe HTML.

echo esc_html( $coupon_title ); // If strictly textual.
?>

Never echo raw database content without escaping.

WAF rule examples and patterns (for immediate virtual patching)

If you manage a WAF, apply rules that target the likely exploit vectors. Test rules in staging to avoid blocking legitimate behaviour.

• Block POST/PUT requests where body contains <script (case-insensitive) or event attributes (onerror=, onclick=, onload=).
• Block submissions containing JavaScript URIs (e.g., données:text/html, javascript :).
• Detect and block encoded payloads that decode to <script ou onerror (base64, hex, URL-encoded).
• Block submissions to admin endpoints that create coupons when payloads include angle-bracketed HTML elements or typical XSS patterns.
• If possible, sanitize outgoing responses that contain mycred_load_coupon renderings by stripping <script> tags before they reach clients.
• Rate-limit or challenge POSTs from Contributor accounts that create or edit coupons repeatedly.
• Use CSP headers to reduce the impact of any inline scripts that may slip through.

Note: effective rules require careful testing to avoid false positives on sites that use legitimate HTML in coupons.

If you’ve found malicious content — step-by-step incident response

1. Take affected page(s) offline or set them to draft.
2. Replace or sanitize the coupon/post entries with clean content.
3. Update myCred to 2.9.7.4 (or higher).
4. Rotate admin/privileged user passwords and force password resets for users who may have viewed impacted pages.
5. Invalidate sessions (force logout).
6. Scan for webshells/backdoors and other malicious files; check modified files and unknown scheduled tasks.
7. Check for outbound network connections to attacker infrastructure and block suspect destinations.
8. Notify stakeholders and follow breach-notification policies where applicable.

What to do if your site uses third-party contributor workflows

• Require editorial approval for all Contributor submissions before publishing.
• Sandbox file upload features — limit allowed file types and perform server-side checks.
• If automation promotes Contributor content to public pages, add a human approval step for content containing shortcodes or HTML.

FAQs: concise answers

Q: Can this XSS be exploited by anonymous visitors?

A: No. Exploitation requires an authenticated user with Contributor privileges or higher to store the malicious payload.

Q: If I update to 2.9.7.4, am I safe?

A: Updating closes the reported vulnerability in the plugin. You must also search for and remove any previously stored malicious content created before the update.

Q: Can a managed firewall block this exploit automatically?

A: A properly configured managed WAF or edge filter can block common exploit attempts and provide virtual patching while you test and deploy the vendor patch. Still, updating the plugin and cleaning stored payloads is required for full remediation.

Q: What if I can’t update because of customisations?

A: Virtual patching with WAF rules, restricting Contributor capabilities, and sanitizing outputs are interim steps. Create a test environment to validate plugin updates against your customisations before rolling out.

Why stored XSS often has outsized impact

Stored XSS is more dangerous than reflected XSS because the payload is persistent — it executes on every page load that renders the stored data. That persistence increases the blast radius:

• A single malicious Contributor account can affect thousands of visitors.
• Attackers can craft targeted payloads to phish admins or to escalate privileges.
• Search engines may index malicious content, amplifying SEO harm.

Long-term recommendations for organisations and hosts

• Establish a plugin update policy and an incident response plan that covers dependency vulnerabilities.
• Adopt role-based controls and periodic role audits — especially on sites accepting user-generated content.
• Maintain a staging and CI pipeline to enable safe plugin upgrades and regression testing.
• Implement CSP and other browser security features to mitigate client-side attacks.
• Centralise security monitoring: aggregate WAF events, updates, and scan results across sites you manage.

Practical examples — searches and commands to run right now

These examples assume SSH and WP-CLI access. Back up before running destructive commands.

-- Find pages using the mycred shortcode:
wp db query "SELECT ID,post_title FROM wp_posts WHERE post_content LIKE '%mycred_load_coupon%';"

-- Search for script tags in posts:
wp db query "SELECT ID,post_title FROM wp_posts WHERE post_content REGEXP '<script[[:space:]]*[^>]*';"
wp db query "SELECT meta_id,post_id,meta_value FROM wp_postmeta WHERE meta_value LIKE '%<script%';"

-- List recent coupon edits (plugin schema may vary):
wp db query "SELECT * FROM wp_posts WHERE post_type = 'coupon' AND post_modified >= '2026-02-01';"

Example temporary capability removal (run as mu-plugin or one-off script):

<?php
// Temporary: remove coupon editing/publishing caps from Contributors.
// Exact capability names depend on plugin implementation.
$role = get_role('contributor');
if ( $role ) {
    $role->remove_cap('edit_coupons');
    $role->remove_cap('publish_coupons');
}
?>

Liste de contrôle finale — ce que vous devez faire maintenant

• Verify whether myCred is installed (and which version) on every site you manage.
• If installed and version ≤ 2.9.7.3: update to 2.9.7.4 immediately (test first).
• If update is not immediately possible: enable WAF rules to block XSS payloads and remove Contributor capability to create coupons.
• Search the database for stored payloads (<script, onerror, javascript :) and remove/sanitize any findings.
• Rotate credentials and force logout for administrators if you have signs of active exploitation.
• Scan for webshells and unusual files; restore from a clean backup if necessary.
• Apply the long-term hardening steps described above.