Summary: A broken access control vulnerability in the Paytium plugin (Mollie integration) up to and including version 4.3.7 allows low-privileged users (Subscriber) to invoke the plugin’s create_mollie_profile functionality. The defect is rated medium severity (CVSS 7.1) and has been resolved in Paytium 4.4. If your site uses Paytium and is not yet updated, treat this as urgent for payment and reconciliation integrity.

In this article

• What “missing authorization” means in practice
• How attackers might exploit the flaw and potential impacts
• Immediate mitigation steps (including mu-plugin and WAF rules)
• Recommended permanent developer fixes
• Incident response and post-incident hardening

Executive summary (quick action checklist)

• Upgrade Paytium to 4.4 or later immediately — this is the single most important action.
• If you cannot update immediately, apply one or more temporary mitigations:
  • Deploy a server-side block for the vulnerable AJAX/REST endpoint (mu-plugin example included below).
  • Deploy WAF rules to block or rate-limit requests referencing create_mollie_profile.
  • Rotate Mollie API credentials if you suspect exposure and review Mollie account activity.
• Audit logs for suspicious calls and unexpected created profiles.
• Follow incident response steps: isolate, investigate, mitigate, and notify where required.
• Developers: implement capability checks, nonces, REST permission callbacks, and tests before releasing changes.

What exactly is “missing authorization” here?

“Missing authorization” (a form of broken access control) means the code that handles a sensitive action fails to verify the caller has sufficient privileges. In this Paytium case, a Subscriber could trigger the create_mollie_profile action — an operation that should require elevated capabilities (for example, administrator or a shop manager), and at minimum strong nonce and contextual checks.

Consequences depend on what the action touches. When payment profiles and customer objects are involved, an attacker can:

• Create attacker-controlled payment profiles or customer objects at the payment provider.
• Cause reconciliation issues, fraudulent transaction conditions, or confusing records.
• Inject unexpected data that later influences backend workflows.
• Combine with other flaws to increase impact.

Even if direct theft isn’t possible from this single bug, the resulting state manipulation can be leveraged for fraud or operational disruption.

Risk assessment

• Vulnerable versions: ≤ 4.3.7
• Fixed in: 4.4 (upgrade immediately)
• CVSS: 7.1 (Medium)
• Required privilege (as reported): Subscriber — low-privileged accounts could exploit
• OWASP category: Broken Access Control
• Typical impact: Integrity (High), Availability (Low), Confidentiality (Variable)

Given payment integrations are involved, treat this as moderate-to-high priority for any site handling donations or payments.

How might an attacker exploit this in practice?

1. Automated probes by low-level accounts
   An attacker registers or compromises Subscriber accounts and storms the endpoint creating Mollie profiles, attempting to manipulate business logic at scale.
2. Profile injection to influence payment flows
   Attacker-created profiles in the payment provider can be used to redirect or obfuscate subsequent payment operations.
3. Abuse combined with social engineering
   A plausible attacker-created donation or profile could be used to trick staff into refunds or reconciliation errors.
4. Supply chain and lateral movement
   Created objects may trigger webhooks or third-party callbacks, expanding attacker reach or revealing data.

Even non-admin exploitation against payment-related operations must be prioritised for remediation.

Detecting exploitation and indicators of compromise

Look for the following in server and application logs:

• POST requests to admin-ajax.php or to the plugin’s REST route containing parameters or actions with create_mollie_profile.
• Requests from Subscriber or unknown accounts that receive success responses from the plugin.
• Unexpected customer/profile objects in the Mollie dashboard linked to unfamiliar emails or your domain.
• Unexpected webhook calls from Mollie referencing newly created profiles.
• New or unusual database rows in plugin tables where Paytium stores profiles or customer IDs.
• Abnormal spikes in requests to plugin endpoints from same IPs or repeating accounts.

Search logs for strings such as:

• action=create_mollie_profile
• create_mollie_profile
• paytium_create_profile
• POSTs to the plugin’s REST path or admin-ajax.php correlated with suspicious user IDs

If you find evidence, follow the incident response steps below immediately.

Immediate mitigation — what to do right now

1. Update Paytium to 4.4 or later — preferred and fastest fix. Test on staging where feasible, but prioritise live payment safety.
2. If you cannot update, deploy a server-side emergency block (mu-plugin). Place the file in wp-content/mu-plugins/deny-paytium-create-profile.php. This intercepts the vulnerable action without editing plugin files.
3. Example mu-plugin

<?php
/**
 * Emergency mitigation: block create_mollie_profile calls from low-privileged users
 * Deploy this as an mu-plugin in wp-content/mu-plugins/
 */

add_action('wp_ajax_create_mollie_profile', 'hksec_block_create_mollie_profile');
add_action('wp_ajax_nopriv_create_mollie_profile', 'hksec_block_create_mollie_profile');

function hksec_block_create_mollie_profile() {
    // Allow only administrators or a specific capability to proceed
    if ( ! is_user_logged_in() || ! current_user_can( 'manage_options' ) ) {
        // Log details for later investigation
        $remote_ip = isset($_SERVER['REMOTE_ADDR']) ? $_SERVER['REMOTE_ADDR'] : 'unknown';
        $user_id = get_current_user_id();
        error_log( sprintf(
            'Blocked create_mollie_profile attempt: user=%d ip=%s uri=%s',
            $user_id,
            $remote_ip,
            (isset($_SERVER['REQUEST_URI']) ? $_SERVER['REQUEST_URI'] : '')
        ) );
        wp_send_json_error( array( 'message' => 'Unauthorized' ), 403 );
        wp_die();
    }

    // If allowed, allow original handler to proceed
}

Note: This mu-plugin denies non-admin attempts. Adjust the capability (for example, manage_woocommerce or a custom capability) if your operational model requires different privileges.

4. Deploy WAF rule(s) — add rules to block or rate-limit requests referencing create_mollie_profile. Use staging to validate rules before production.

Sample ModSecurity rule (conceptual; test before use):

# Block requests attempting to call create_mollie_profile actions
SecRule REQUEST_URI|ARGS_NAMES|ARGS "@contains create_mollie_profile" "id:1001001,phase:1,deny,log,status:403,msg:'Blocked possible Paytium create_mollie_profile exploit',tag:'waf:paytium'"

# More targeted: block POSTs to admin-ajax.php with specific action
SecRule REQUEST_FILENAME "@endsWith admin-ajax.php" "phase:2,chain,log,deny,status:403,id:1001002,msg:'Blocked admin-ajax create_mollie_profile POST'"
SecRule ARGS:action "@streq create_mollie_profile"

WAF rules can create false positives. Monitor logs and adjust rules carefully. Prefer “monitor” mode initially.

5. Short-term policy: disable or limit user registrations — if open registration is used and abused, require admin approval or temporarily disable registration.
6. Rotate Mollie API keys and webhooks — if you see evidence of abuse or attacker-created objects, rotate keys in Mollie and update the plugin after remediation.

Permanent developer fixes (recommended coding changes)

Ensure proper, layered authorization and validation for sensitive operations:

1. Capability checks: ensure only appropriate roles/capabilities can call sensitive functions. Example for Ajax handlers:

   add_action( 'wp_ajax_create_mollie_profile', 'paytium_create_mollie_profile_handler' );
   
   function paytium_create_mollie_profile_handler() {
       if ( ! current_user_can( 'manage_options' ) ) {
           wp_send_json_error( array( 'message' => 'Unauthorized' ), 403 );
           wp_die();
       }
       // Continue...
   }

2. Nonce verification: use nonces for actions triggered from front-end or admin forms.

   if ( empty( $_REQUEST['paytium_nonce'] ) || ! wp_verify_nonce( sanitize_text_field( wp_unslash( $_REQUEST['paytium_nonce'] ) ), 'paytium_create_profile' ) ) {
       wp_send_json_error( array( 'message' => 'Invalid nonce' ), 403 );
       wp_die();
   }

3. REST API permission callbacks:

   register_rest_route( 'paytium/v1', '/profile', array(
       'methods'  => 'POST',
       'callback' => 'paytium_rest_create_profile',
       'permission_callback' => function() {
           return current_user_can( 'manage_options' );
       },
   ) );

4. Input validation and sanitization: whitelist and strictly validate inputs before use.
5. Principle of least privilege: avoid exposing admin-level operations to subscriber-level inputs; if necessary, implement strict server-side business rules and rate limiting.
6. Automated tests: add unit/integration tests that assert unauthorized users cannot perform restricted actions.
7. Logging and monitoring: structured logging of sensitive ops (user id, IP, user agent, timestamp) for quick investigation.

Example code for a robust handler (illustrative)

function paytium_create_mollie_profile_handler() {
    // Must be logged in
    if ( ! is_user_logged_in() ) {
        return wp_send_json_error( array( 'message' => 'Not authenticated' ), 401 );
    }

    // Capability check: only allow administrators / shop managers
    if ( ! current_user_can( 'manage_options' ) ) {
        return wp_send_json_error( array( 'message' => 'Insufficient privileges' ), 403 );
    }

    // Nonce check (if front-end forms are used)
    if ( empty( $_POST['paytium_nonce'] ) || ! wp_verify_nonce( sanitize_text_field( wp_unslash( $_POST['paytium_nonce'] ) ), 'paytium_create_profile' ) ) {
        return wp_send_json_error( array( 'message' => 'Invalid nonce' ), 400 );
    }

    // Validate input
    $email = isset( $_POST['email'] ) ? sanitize_email( wp_unslash( $_POST['email'] ) ) : '';
    if ( ! is_email( $email ) ) {
        return wp_send_json_error( array( 'message' => 'Invalid email' ), 400 );
    }

    // Do rate limiting / logging here

    // Create profile via Mollie API using properly stored credentials
    // ... implementation ...
}

Apply the pattern: authentication → capability → nonce → sanitize/validate → log for any operation that alters payment provider state.

Incident response — step-by-step

1. Isolate and mitigate
   • Patch to Paytium 4.4 immediately, or deploy the mu-plugin mitigation and WAF rules above.
   • Temporarily disable public registration if abused.
2. Preserve logs and evidence
   • Export web server logs, access logs, plugin logs, and database backups.
   • Record timestamps, IPs, user IDs, and request payloads.
3. Investigate scope
   • Query the database for created profiles and suspicious entries.
   • Check Mollie dashboard for new customers/profiles and API calls.
   • Determine whether funds moved, webhooks were triggered, or other systems were affected.
4. Clean and restore
   • If persistence is found, restore from a known clean backup.
   • Rotate secrets: Mollie keys, any exposed API tokens, and admin credentials where required.
5. Notify stakeholders
   • Inform internal security, hosting provider, and affected users as required by contract or law.
6. Postmortem and patch
   • Document root cause, timeline, and remediation steps. Apply permanent fixes and tests.
7. Re-scan and monitor
   • Run a full compromise/malware scan and continue monitoring for re-attempts from same IPs or accounts.

WAF rule design and best practices

When designing WAF rules to mitigate this class of vulnerability:

• Focus on request intent and known indicator strings (e.g., create_mollie_profile or the plugin REST path) rather than blocking broad request classes.
• Prefer deny for confirmed malicious patterns and rate limiting for suspicious-but-possibly-legitimate traffic.
• Add logging and alerting to capture blocked attempts for forensic analysis.
• Test rules in monitor/log-only mode before enabling deny to avoid service disruption.
• Maintain clear exception lists for internal IPs and trusted automation.

Suggested approach:

• Block unauthenticated requests that reference create_mollie_profile.
• Rate limit authenticated requests that perform profile creation (e.g., 5/hour per user).
• Alert on sudden spikes of successful profile creations.

Hardening recommendations (beyond this vulnerability)

• Keep WordPress core, plugins, and themes up to date.
• Enforce strict role/capability discipline and audit user roles regularly.
• Enable two-factor authentication for administrators and privileged users.
• Enforce TLS sitewide and HSTS where possible.
• Isolate payment processing to dedicated roles/systems when feasible.
• Remove unused or legacy plugins; maintain minimal plugin footprint.
• Maintain regular backups and test restores.
• Monitor for unusual payment, reconciliation, or webhook activity.
• Consider using managed WAF and professional security services if you lack in-house capability.

Developer checklist — security controls to implement

• Authorization: every action has a clear authorization decision (current_user_can or permission_callback).
• Authentication: verify the user is authenticated when required.
• Nonce protection: use nonces for state-changing operations.
• Input validation: whitelist inputs and validate types/formats.
• Output escaping: escape outputs according to the context (HTML/JS/SQL).
• Rate limiting: protect endpoints that can be abused.
• Logging: log critical operations for audit and forensic analysis.
• Tests: unit/integration tests that assert unauthorized users cannot perform restricted actions.
• Dependency updates: keep third-party libraries and SDKs current.
• Secret management: store keys in secure storage or environment variables, not in repo.
• Incident plan: maintain a documented and tested incident response plan.

Frequently asked questions

Q: I updated to 4.4 but still see suspicious activity — what should I do?

A: The update removes the access control flaw but you must investigate whether exploitation occurred prior to the update. Rotate credentials, review Mollie data, check logs, and follow the incident response steps above.

Q: Will disabling Paytium until I can update fix the issue?

A: Disabling or removing the plugin removes the vulnerable code path. However, if the site was already exploited, disabling alone does not remediate persistence or data discrepancies. Investigate and clean as required.

Q: I don’t have developer resources to apply code changes. What can I do?

A: Deploy the mu-plugin mitigation and WAF rules described above, restrict registrations, rotate keys, and engage a trusted security consultant or your host for assistance.

Closing thoughts

Broken access control is a common and potentially severe category of vulnerability, particularly when payment systems are involved. The Paytium issue highlights the importance of layered defenses: secure coding, rapid patching, targeted WAF rules, structured logging, and a tested incident response playbook.

If your site uses Paytium (≤ 4.3.7), upgrade to 4.4 or later immediately. If you cannot update right away, apply the emergency mitigations in this article, deploy targeted WAF rules, rotate secrets if needed, and monitor logs for signs of abuse.

If you need assistance beyond your in-house capability, engage your hosting provider or a reputable security consultant to help implement mitigations and perform an incident investigation.