On 16 February 2026 a broken access control vulnerability affecting the Uni CPO (Premium) plugin for WooCommerce was disclosed (CVE-2025-13391). Versions up to and including 4.9.60 are affected. The flaw permits unauthenticated actors to perform privileged actions such as uploading arbitrary attachments and deleting files synced with Dropbox because certain plugin endpoints failed to validate authentication/authorization and nonce checks.

This write-up provides a practical, technical briefing for site owners, administrators, agencies and hosts. It explains the impact, attack vectors, detection signals, immediate containment steps and long-term hardening advice from a Hong Kong security perspective. A vendor fix is available — update immediately where possible; for environments that cannot update at once, apply containment and virtual patching via your WAF or host.

Resumen (hechos rápidos)

• Affected software: Uni CPO (Premium) plugin for WooCommerce
• Vulnerable versions: ≤ 4.9.60
• Fixed in: 4.9.61
• CVE: CVE-2025-13391
• Weakness category: Broken Access Control (OWASP A1)
• CVSSv3 Base Score (reported): 5.8 (Medium)
• Privilegio requerido: No autenticado (sin inicio de sesión requerido)
• Impact examples: Arbitrary attachment upload, deletion of Dropbox-synced files
• Disclosure date: 16 Feb 2026

Por qué esto es importante

Broken access control bypasses expected permissions. In this case:

• Unauthenticated file upload can lead to malicious files, web shells, supply-chain or content poisoning if attachments are used on product pages or downloads.
• Unauthorized deletion of Dropbox-synced files can destroy backups, product assets or other critical assets stored remotely, causing business disruption.

Because the plugin integrates with Dropbox, both local site content and third-party storage can be affected.

Cómo funciona la vulnerabilidad (visión técnica)

Understanding the root cause helps administrators fix and harden systems without publishing exploit code.

Common causes for broken access control in similar WordPress plugins:

• AJAX or REST endpoints registered without capability checks or without a proper permiso_callback para rutas REST.
• Missing or improperly validated nonces. Nonces alone are not sufficient but are part of intent validation.
• Endpoints performing file operations or acting on stored Dropbox tokens but failing to verify the requester’s authentication/authorization.

Result: a crafted HTTP request (often POST) to the vulnerable endpoint can upload files or trigger delete operations against Dropbox using stored credentials.

Typical implementation mistakes:

• Usar register_rest_route() con permiso_callback omitted or set to __devolver_verdadero.
• AJAX actions handled without current_user_can(...) checks or wp_verify_nonce().
• Dropbox routines that call the API using stored tokens without ensuring the caller is authorized.

Immediate steps you must take (ordered by priority)

1. Update the plugin to 4.9.61 (or later). This is the highest-priority action — the vendor patch addresses access control checks. Verify changelogs and apply updates promptly.
2. If you cannot update immediately: contain the risk.
   • Disable the plugin temporarily on public-facing sites until you can update.
   • If disabling is not feasible, apply virtual patching at the edge using your Web Application Firewall (WAF) or host firewall (examples below).
3. Rotate Dropbox and third-party tokens. Assume tokens may have been abused. Revoke and re-issue API tokens in Dropbox and update plugin settings after you patch.
4. Scan for indicators of compromise (IoC) and suspicious uploads. Check uploads, webserver logs, plugin logs and Dropbox activity (detection section below).
5. Backups & restore plan. Ensure clean, tested backups exist. If compromise is found, restore from a snapshot created before the intrusion.
6. Harden administrative endpoints. Restrict access to admin-ajax.php and plugin REST endpoints with IP allowlists where possible and enforce authentication for backend-only endpoints.

Detection: What to look for (Indicators of Compromise)

Check these areas first:

• Webserver access logs: Busca solicitudes POST a admin-ajax.php or plugin REST paths from unusual IPs or suspicious user agents. Watch for parameters like action=[plugin_action_name] or REST calls to /wp-json/uni-cpo/.
• WordPress and plugin logs: Search for Dropbox API calls, delete responses (204), errors or unexpected API activity.
• wp-content/uploads: Newly created files with odd extensions (.php disguised as .jpg, double extensions) or unexpected modification times.
• Dropbox account activity: Review app activity, file deletions, API calls and token usage in the associated Dropbox account.
• File integrity and malware scans: Run full scans for webshells, obfuscated PHP and unusual cron jobs.
• Cambios en la base de datos: Look for unexpected option changes, new admin users or modified settings that store tokens.

If evidence of exploitation exists: isolate the site, preserve logs, rotate secrets, remove malicious files, restore from a clean backup and harden before returning to production.

Practical virtual patching / WAF mitigation (generic guidance)

If immediate updating is not possible, apply virtual patches using your WAF, host firewall or reverse proxy. The goal is to block unauthenticated requests from reaching vulnerable code paths.

High-level mitigation goals:

• Block unauthenticated requests that attempt to call plugin actions performing file operations.
• Block unauthenticated requests to Dropbox-related endpoints or plugin AJAX handlers.
• Require valid authentication cookies or nonces for sensitive endpoints.

Example rule ideas (pseudo-rules — adapt to your WAF/host tooling):

• Block requests to admin-ajax.php where:
  • El método HTTP es POST
  • Parameter parámetro de matches the plugin’s sensitive actions (e.g., upload_attachment, delete_dropbox_file)
  • Request lacks WordPress authentication cookies (wordpress_logged_in_*) or a valid nonce header
• Block unauthenticated REST calls:
  • Block requests to /wp-json/uni-cpo/* if they come without valid authentication, contain upload/delete parameters, or originate from suspicious user agents
• Rate-limit suspicious endpoints: apply strict per-IP rate limits for endpoints that handle file operations.
• Block known exploit signatures: detect multipart/form-data uploads containing executable file types or unexpected content when targeting plugin endpoints.

Illustrative ModSecurity-style rule (example only — test in staging before production):

SecRule REQUEST_METHOD "POST" "chain,deny,status:403,id:100001,msg:'Block Uni CPO unauthenticated upload action'
  SecRule ARGS:action \"(?:uni_cpo_upload_attachment|uni_cpo_delete_dropbox)\" \"chain,log,tag:'uni-cpo-mitigation',severity:2\"
  SecRule &REQUEST_COOKIES:/wordpress_logged_in_/ \"@eq 0\""

Notas:

• Adapt names of actions and REST namespaces to match the plugin’s actual routes.
• Test rules on staging first to avoid false positives that could block legitimate users or integrations.
• When creating WAF rules, whitelist trusted IPs (e.g., your admin team) and maintain an override path for emergency access.

Recommended hardening and best practices beyond the immediate fix

• Principio de menor privilegio: Limit which accounts and processes have access to Dropbox tokens and API credentials.
• Gestión de tokens: Use short-lived tokens where possible and store secrets securely (environment variables, secret stores) rather than in world-readable options.
• Reducir la superficie de ataque: Disable or remove plugin features you do not use (external integrations, upload endpoints).
• Separate concerns: Use service accounts for integrations so rotation and auditing are manageable.
• Periodic scans and integrity checks: Implemente monitoreo de integridad de archivos y escaneos programados de malware.
• Defensa en profundidad: Combine host hardening, proper file permissions, code reviews and a WAF.
• Pruebas y ensayo: Test plugin upgrades and WAF rules in staging; maintain rollback plans.

How to check whether your site has been targeted (audit checklist)

1. Confirme la versión del plugin: Dashboard > Plugins, lista de plugins de wp, or inspect wp-content/plugins/uni-woo-custom-product-options-premium/readme.txt.
2. Search logs: Grep for admin-ajax.php calls with plugin-specific action names and POSTs to plugin REST paths like /wp-json/uni-cpo/.
3. List new files: find wp-content/uploads -type f -mtime -7 (adjust days) and inspect for PHP or suspicious content.
4. Inspect Dropbox account: Review app access logs for deletions, API calls and token grants.
5. Run malware scan: Use server-side scanners and WP-focused detectors; focus on wp-content/uploads and wp-admin.
6. Check scheduled tasks and users: lista de eventos cron de wp and wp user list for anomalies.
7. Rotar credenciales: Revoke and reissue Dropbox tokens, API keys and any plugin-specific secrets.

If compromise is detected, document timestamps and preserve logs. Engage incident response if customer data or persistent backdoors are suspected.

Developer guidance — fixing and preventing similar errors in code

For plugin and custom-code maintainers, adopt these secure coding practices:

1. REST API routes: Always supply a secure permiso_callback to register_rest_route(); do not use __devolver_verdadero.

   register_rest_route( 'uni-cpo/v1', '/upload', array(
     'methods'  => 'POST',
     'callback' => 'uni_cpo_handle_upload',
     'permission_callback' => function() {
       return current_user_can( 'manage_options' ); // appropriate capability
     }
   ) );

2. Acciones AJAX: Uso check_ajax_referer( 'your-nonce-name', 'security' ); and always validate current_user_can() before privileged operations.
3. Dropbox and external APIs: Treat token-using actions as privileged. Only allow token usage from authenticated admin sessions or trusted background jobs.
4. Validate file uploads: Use a strict whitelist for file types, disallow executable uploads to public directories, rename stored files and scan uploads for malware patterns.
5. Registro y monitoreo: Log actions against external services (who, what, when). Retain logs for incident response.

Timeline & severity context

• Discovery and disclosure: 11–16 February 2026 (disclosed 16 Feb 2026)
• CVE assigned: CVE-2025-13391
• Severity: Medium (CVSS 5.8). The vulnerability enables unauthenticated file operations; confidentiality impact is limited by default, but uploads can be escalated to RCE depending on hosting and configuration.

Note: CVSS is a baseline — real-world impact can be higher if attackers leverage upload vectors for code execution or persistence.

Recovery and cleanup checklist (if you find evidence of exploitation)

1. Isolate the site (remove from public DNS or put behind maintenance mode / firewall).
2. Preserve logs (webserver, WP debug, plugin logs, Dropbox activity).
3. Change all associated credentials (Dropbox, plugin-specific keys, WordPress admin passwords).
4. Remove malicious files (search for webshell signatures, obfuscated PHP, unusual cron jobs).
5. Restore from a clean backup if you cannot confidently clean the site.
6. Update plugin to 4.9.61 or later and update all plugins/themes.
7. Re-scan after update and cleanup.
8. Monitor the site closely for recurrence.
9. Rotate tokens for other connected services.

Recomendaciones finales (lista de verificación de acciones)

• Update Uni CPO (Premium) to version 4.9.61 or later — do this immediately where possible.
• If you manage multiple sites, schedule and push updates or disable the plugin until patched.
• Rotate third-party tokens (Dropbox etc.) that were connected to the plugin.
• Apply WAF rules or host-level blocks to virtually patch the issue if you cannot update immediately.
• Audit and scan for signs of compromise using the detection checklist above.
• Implement developer hardening steps to prevent similar coding mistakes in the future.