Nom du plugin	Paid Member Subscriptions
Type de vulnérabilité	Contrôle d'accès brisé
Numéro CVE	CVE-2025-11835
Urgence	Faible
Date de publication du CVE	2025-11-04
URL source	CVE-2025-11835

Urgent: Protect WordPress Sites Against CVE-2025-11835 — Paid Member Subscriptions <= 2.16.4 Missing Authorization (Unauthenticated Auto-Renewal)

Auteur: Équipe de sécurité WP-Firewall
Date: 05 November 2025

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Résumé

• A broken access control vulnerability (CVE-2025-11835) affecting the Paid Member Subscriptions WordPress plugin (versions ≤ 2.16.4) allows unauthenticated attackers to trigger or change a member subscription’s auto-renewal state.
• Severity: Low (CVSS 5.3) — but context matters: membership sites, recurring payments, and user trust can magnify the impact.
• Fixed in: 2.16.5 — update immediately if you run this plugin.
• If you cannot update right away, WP-Firewall can provide immediate mitigations (managed WAF rules and virtual patching) to block exploit attempts and reduce risk.

This post explains how the vulnerability works, the realistic risks for WordPress sites, detection options, short-term mitigations, and long-term best practices. It also outlines what WP-Firewall can do to protect your site while you patch.

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What happened: vulnerability in plain words

The Paid Member Subscriptions plugin exposes an endpoint or function that changes the “auto-renewal” flag on subscriptions. Because the plugin failed to enforce proper authorization or nonce verification on that operation, unauthenticated attackers could call the endpoint and flip the auto-renewal state for arbitrary subscription records.

In practical terms, an attacker could:

• Turn on auto-renewal for a subscription that the owner had disabled (potentially charging the user unexpectedly), or
• Turn off auto-renewal, causing a subscription to lapse and member access to be lost.

This is a broken access control issue — the plugin executes a privileged action without verifying whether the caller is allowed to do so.

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Why this matters (real-world impact)

Although the CVSS score is moderate, the business and user impact can be significant depending on the website:

• Financial & billing issues: Changing a subscription’s auto-renewal could trigger or prevent recurring charges. This can cause unexpected billing for customers or loss of recurring revenue for merchants.
• Customer support load: Users who lose access or are billed unexpectedly will contact support. Volume may be high for membership-heavy sites.
• Reputation damage: Billing errors or unexpected account changes harm trust, especially for paid communities and online courses.
• Legal & compliance risks: Unauthorized changes in payment settings may violate payment provider terms or consumer protection rules in some jurisdictions.
• Chained exploitation: If attackers can manipulate subscriptions at scale, they may combine this with social engineering, fraudulent chargeback attempts, or targeted harassment of specific users.

En résumé : even “low severity” access-control bugs can have outsized operational impact in subscription-based services.

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Technical analysis (how the issue works)

Note: we will explain the vulnerability conceptually so technical defenders can mitigate — not provide exploit recipes.

• Vulnerability class: Broken Access Control (missing authorization check).
• A plugin function or AJAX action (front-end/back-end) accepts a subscription identifier and an auto-renew flag and performs an update.
• The function fails to verify:
  • That the request is from an authenticated, authorized user (owner or site admin).
  • That any required nonce or capability check is present and valid.
• As a result, an unauthenticated HTTP request can trigger the internal update logic, modifying database fields associated with subscriptions.

Common patterns that produce this class of vulnerability:

• Registering an AJAX action with wp_ajax_nopriv without proper parameter and capability validation.
• Implementing a REST endpoint and omitting permission_callback or returning true incorrectly.
• Accepting POST/GET variables and performing db updates with minimal sanitization and no authorization check.

Typical vulnerable endpoint characteristics:

• POST or AJAX endpoint under /wp-admin/admin-ajax.php or plugin-specific REST routes.
• Parameters include subscription_id, auto_renew (or similar).
• No check that get_current_user_id() == owner_id, or no check_user_can('edit_user') / appropriate capability.
• Missing or invalid nonce verification.

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Indicators of compromise (IoCs) & detection

Look for suspicious requests in server and application logs. Key indicators:

• Requests to admin-ajax.php or the plugin’s REST route with parameters like subscription_id, sub_id, auto_renew, auto_renewal, recurring, renew, renewal.
• High volume of requests to the same endpoint from single IPs or distributed requests targeting multiple subscription IDs.
• Unexpected changes in subscription meta fields: auto_renew toggled without matching user action.
• Payment gateway webhooks indicating charge attempts where a user had previously disabled auto-renew.
• Spike in support requests about unexpected charges or lost access.

Example patterns to search in logs:

• URL containing admin-ajax.php et action=... where action maps to subscription updates.
• POST payloads with keys: subscription_id, auto_renew, renew_status.
• Requests with no authenticated session cookies but performing state changes (no WP logged-in cookie header or session).

Practical detection tips:

• Use the WP-Firewall or WAF logs to filter blocked/allowed traffic to membership plugin endpoints.
• Monitor database audit logs (if available) or the plugin’s logs for changes to subscription entries.
• Implement regular checks comparing subscription auto_renew values with historical user preferences (anomaly detection).

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Exploitation scenarios (threat models)

1. Opportunistic attacker scanning the internet:
   • Automated tools fuzz plugin endpoints. If they find the vulnerable route, they toggle auto-renewal on many accounts. Result: billing chaos or service denial.
2. Targeted attacker against high-value membership:
   • Attacker toggles auto-renew off for VIP accounts before an important renewal, causing access disruption and reputational damage.
3. Fraudster seeking billing advantage:
   • Switch auto-renew on for free trials or inactive payment instruments to trigger unexpected charges or abuse billing workflows.
4. Combined attacks:
   • Toggle renewals, then spam the site’s support or engineer chargebacks to exploit refund processes or create financial confusion.

Each scenario yields different priorities for mitigation but all require immediate attention.

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Immediate remediation (what to do now)

1. Mettre à jour le plugin
   • The vendor released version 2.16.5 with the fix. Update Paid Member Subscriptions to 2.16.5 or later immediately on all affected sites.
   • Test updates on staging before production if you have a complex setup or add-ons.
2. If you cannot update immediately, apply these temporary mitigations:
   • Block access to the vulnerable endpoint with WAF rules (see WP-Firewall mitigations below).
   • Add server-side access restrictions: deny external access to plugin-specific REST endpoints or admin-ajax.php actions used by the plugin unless the request is authenticated and from valid origins.
   • Rate-limit and throttle requests to subscription endpoints.
   • Monitor for changes to subscription auto_renew fields and enable alerts.
   • Consider temporarily suspending automated billing or adding a manual approval step if you detect suspicious activity.
3. Informer les parties prenantes
   • Communicate to internal and customer support teams so they can quickly respond to errant billing or access reports.
   • Maintain an incident log (who, what, when) for transparency and post-incident review.

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How WP-Firewall protects you (managed WAF and virtual patching)

If you use WP-Firewall, here’s how we can help immediately and during the remediation process:

• Managed WAF rules: we rapidly deploy tuned rules that block suspicious POST/REST requests targeting subscription endpoints where authorization should exist. This stops exploitation attempts without waiting for a plugin update.
• Virtual patching: our virtual patching (vPatching) prevents attacks by intercepting malicious requests and neutralizing them before they reach the plugin code.
• Signature updates: we maintain signature databases for common patterns (e.g., suspicious parameter names and action names) and can apply them globally or per-site.
• Malware scanner & monitoring: continuous scans will detect suspicious changes in plugin files or database rows and trigger alerts.
• Traffic analytics: identify unusual spikes to subscription endpoints, spot scanning behavior, and track blocked attempts.
• Custom rulesets: for high-risk sites, we can implement business-specific rules, e.g., only allow auto-renew toggles from logged-in users with matching user IDs or known IPs.

Example WAF mitigation techniques we recommend:

• Block unauthenticated POSTs to specific AJAX actions or REST routes the plugin exposes.
• Enforce presence of valid WP nonces for actions that change subscription state (if the request lacks a nonce, block).
• Block requests with missing or invalid cookies to endpoints that require authentication.
• Rate-limit calls to subscription endpoints per IP and per endpoint.
• On detection: log and alert, and optionally present a CAPTCHA step for suspected automation.

WP-Firewall’s managed protection buys time for safe testing and deployment of official patches.

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Recommended WAF rule examples (conceptual)

Below are conceptual examples of rules you can implement in a WAF. Do not paste these into production without testing in staging.

1. Block unauthenticated POSTs to admin-ajax action:
   • Condition:
     • Request path contains /wp-admin/admin-ajax.php
     • POST body contains action parameter with values matching subscription update actions (e.g., update_auto_renew, set_subscription_renewal)
     • No WP logged-in cookie present OR nonce missing
   • Action : Bloquer et consigner
2. Block REST calls to plugin endpoints without permission check:
   • Condition:
     • Request path matches /wp-json/paid-member-subscriptions/* or plugin-specific namespace
     • HTTP method POST/PUT/PATCH
     • Missing Authorization header or nonce header
   • Action: Block and alert admin
3. Rate-limit:
   • Condition:
     • More than N requests to subscription endpoints from same IP in timeframe T
   • Action: Temporarily block or challenge via CAPTCHA
4. Anomaly detection:
   • Condition:
     • A single remote IP toggles auto_renew status for more than M unique subscription IDs in 1 hour
   • Action: Block, notify security team, create alert ticket

These conceptual rules can be tuned for your environment by WP-Firewall engineers.

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Post-exploitation detection and response

If you suspect exploitation, take these steps:

1. Snapshot & preserve evidence
   • Export relevant server and web logs for the time window.
   • Export plugin logs and database snapshots for subscriptions table and related user meta.
2. Revert unauthorized changes
   • For subscriptions incorrectly toggled:
     • If you have backups of the subscription table, restore affected records or run SQL updates to correct the auto_renew field based on user history or confirmation.
     • Contact affected users to confirm desired renewal preferences.
3. Review payment gateway activity
   • Look for unexpected recurring charge attempts or refunds and coordinate with your payment processor.
4. Audit plugin and WP admin access
   • Ensure no privileged accounts were compromised.
   • Rotate any compromised credentials and enforce strong authentication (2FA).
5. Monitor for follow-on attacks
   • Attackers often pivot. Keep an eye on account modifications, new admin accounts, file changes, and suspicious outbound traffic.
6. After-action review
   • Document root causes and update change control, plugin evaluation, and monitoring policies.

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Hardening membership sites: long-term best practices

1. Keep plugins and core up to date
   • Apply security updates promptly; schedule weekly checks if you operate many sites.
2. Principe du moindre privilège
   • Avoid granting more capabilities than necessary to plugin roles and service accounts.
3. Use nonces and permission callbacks
   • When developing or auditing plugins, verify REST endpoints include permission_callback and actions include nonce checks.
4. Restrict admin ajax and REST where possible
   • Harden REST endpoints and require authentication for any state-changing requests.
5. Two-factor authentication
   • Apply 2FA to administrative users to reduce risk from credential theft.
6. Monitor critical data tables
   • Set alerts for unexpected changes to subscriptions, orders, and billing metadata.
7. Regular backups and tested restores
   • Ensure backups include database snapshots and that restore procedures are tested.
8. Security staging process
   • Test plugin updates in staging, monitor for compatibility issues, then deploy to production with a rollback plan.

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Communications template for support teams

If users report unexpected billing or access issues, use a clear, concise template:

Subject: Regarding your subscription status

Hi [User First Name],

We recently discovered a security issue affecting one of our site’s membership plugins. This may have caused unexpected changes to subscription auto-renew settings.

We’re investigating and have taken immediate steps to protect accounts. Please reply and confirm whether you want auto-renew enabled for your subscription ending on [date]. If you were charged unexpectedly, we will assist with refunds per our policy.

Thank you for your patience — we’re treating this with high priority.

Best,
[Support Team / Security Team]

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Testing and validation after patching

After updating to plugin version 2.16.5 (or later), validate:

• The plugin no longer responds to unauthenticated requests attempting to change auto-renew values.
• Permission checks and nonce validations are present on endpoints that change state.
• Billing workflows behave as expected in staging with test payment methods.
• WAF rules can be relaxed only after confirming patch mitigates the issue.

Recommended test checklist:

• Attempt an unauthenticated POST to the known endpoints — must be blocked or not change server state.
• Attempt authenticated legitimate update — must succeed.
• Run a WordPress health and audit plugin to verify no other vulnerabilities introduced.

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Why some sites still need WAF / virtual patching even after updates

• Delayed rollout: Large fleets and managed hosts take time to push updates. Attackers move fast.
• Compatibility concerns: Some admins delay updates to avoid breaking custom integrations.
• Zero-day risks: New vulnerabilities appear frequently; a proactive WAF adds a protective layer.
• Defense-in-depth: Patching is essential, but layered controls (WAF, monitoring, authentication policies) reduce blast radius.

WP-Firewall’s protection works with your update cadence. We recommend the WAF remain active even after patching to provide ongoing protection against future threats.

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Legal & compliance considerations

• If your users’ billing or personal data has been affected, check applicable notification obligations and payment processor contractual requirements.
• Document remediation steps and communications for audits.
• Consult legal counsel if you suspect widespread billing or financial fraud.

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Final checklist — immediate actions for admins

1. Identify all WordPress sites using Paid Member Subscriptions.
2. Update the plugin to 2.16.5 or later immediately.
3. If you can’t update now:
   • Enable WP-Firewall or other WAF controls to block unauthenticated access to subscription endpoints.
   • Rate-limit and monitor endpoint traffic.
4. Search server and plugin logs for signs of exploitation (sudden toggles of auto-renew).
5. Communicate with support and payment teams; monitor charge activity.
6. Validate fixes in staging and production after applying patches.

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Secure your membership revenue with WP-Firewall — start with the free protection plan

Protecting subscription-based businesses starts with basic but reliable defenses. WP-Firewall’s Basic (Free) plan delivers essential protection: a managed firewall, an intelligent WAF, unlimited bandwidth, malware scanning, and mitigation against OWASP Top 10 risks — everything a small membership site needs for baseline security. If you run a site with subscriptions, enable our free plan today and get immediate protection while you patch plugins and perform deeper security checks: https://my.wp-firewall.com/buy/wp-firewall-free-plan/

Consider upgrading to Standard for automated malware removal and IP allow/block management, or Pro for monthly security reports and automatic virtual patching to minimize downtime and manual work.

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About WP-Firewall (short)

We are the WordPress security team behind WP-Firewall. We focus on practical protection that keeps sites online and safe without slowing them down. Our approach blends managed WAF rules, virtual patching, continuous monitoring, and hands-on support for membership and ecommerce sites where availability and correct billing are mission-critical.

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Credits & references

• Vulnerability: CVE-2025-11835
• A security researcher reported this issue responsibly and the plugin author released a fix in version 2.16.5. We strongly encourage all site owners to update and follow the guidance above.

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If you want help applying temporary WAF rules, creating detection alerts, or validating that the plugin update has fully remediated the issue, the WP-Firewall team is available to assist. Sign up for the free protection plan (or upgrade for automated virtual patching) at: https://my.wp-firewall.com/buy/wp-firewall-free-plan/

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Appendix A — Useful technical checks (SQL snippets and curl examples for defenders)

Note: These are defensive checks for administrators only.

1. Find subscriptions with recent auto_renew changes (example SQL — adapt to your table schema):

   SELECT id, user_id, auto_renew, updated_at
   FROM wp_pms_subscriptions
   WHERE updated_at >= NOW() - INTERVAL 7 DAY
   ORDER BY updated_at DESC;

2. Check for unauthenticated POST attempts in access logs:

   grep "admin-ajax.php" /var/log/nginx/access.log | grep -E "action=.*renew|subscription"

3. Simulate an authenticated update (use only for testing on staging):

   curl -X POST "https://your-site.com/wp-admin/admin-ajax.php" 
     -H "Cookie: wordpress_logged_in=YOUR_TEST_COOKIE" 
     -d "action=update_subscription&subscription_id=123&auto_renew=1&_wpnonce=VALID_NONCE"

   Replace with staging credentials and nonces. The request should succeed only when properly authenticated and include a valid nonce.

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We hope this helps you understand the risk and take immediate steps to protect your membership site. Stay safe, and reach out if you want help configuring WAF rules or setting up monitoring for subscription endpoints.