Critical Update: Broken Access Control Vulnerability in “Subscriptions & Memberships for PayPal” Plugin (Versions ≤1.1.7)

At Managed-WP, our security experts provide thorough analysis of CVE-2025-66107—a broken access control vulnerability impacting the Subscriptions & Memberships for PayPal WordPress plugin up to version 1.1.7. This report outlines the security risk, detection strategies, and essential mitigations including WAF virtual patching you need to act on immediately.

Author: Managed-WP Security Team
Date: 2025-11-28
Tags: WordPress, Plugin Vulnerability, Managed-WP, WAF, Broken Access Control, Security

Overview: A broken access control vulnerability identified as CVE-2025-66107 affects the Subscriptions & Memberships for PayPal plugin versions 1.1.7 and earlier. The vendor has released version 1.1.8 containing the necessary fix. Classified under OWASP’s A1 category, this unauthenticated flaw scores a CVSS of 5.3, highlighting moderate risk due to its ability to bypass authorization checks. This post details exploitation risks, detection methods, and recommended protection steps, emphasizing immediate patching and proactive virtual patch application.

Why This Vulnerability Demands Your Attention

If you operate a WordPress site running the Subscriptions & Memberships for PayPal plugin without upgrading to version 1.1.8 or later, your site is vulnerable to broken access control. This flaw permits unauthorized users to execute actions normally restricted to privileged accounts, potentially leading to privilege escalation, unauthorized subscription modifications, or manipulation of payment processes.
Even vulnerabilities labeled as “low” urgency pose significant operational risks when they allow unauthenticated access, enabling attackers to exploit them without logging in.

Understanding Broken Access Control

Broken access control occurs when the software fails to properly enforce permission checks. Common manifestations include:

• Admin-only functions accessible without login or privilege validation.
• Lack of capability checks such as missing current_user_can() or absent wp_verify_nonce() checks on admin endpoints.
• Endpoints exposed via admin-ajax.php, REST APIs, or custom handlers without sufficient credential verification.
• Direct access to backend files or routes that should be restricted but are publicly accessible.

The result is unauthorized operations performed by malicious actors, jeopardizing the security and integrity of your site’s subscription and payment infrastructure.

Quick Facts About the Vulnerability

• Affected Plugin: Subscriptions & Memberships for PayPal
• Versions Impacted: ≤ 1.1.7
• Patch Available From: 1.1.8
• CVE ID: CVE-2025-66107
• Vulnerability Category: Broken Access Control (OWASP A1)
• Authentication Required: None (Unauthenticated)
• CVSS Score: 5.3 (Medium/Low depending on context)

Note: “Unauthenticated” means attackers need no login credentials to exploit this flaw, making urgent patching and compensating protections critical.

Potential Attack Vectors

1. Automated Scanning and Discovery
   • Attackers script scans on public WordPress sites, probing for vulnerable versions using AJAX or REST endpoints.
2. Subscription and Payment Tampering
   • Exploiters can manipulate subscription states or mock payment confirmation, bypassing revenue controls.
3. Unauthorized Account Manipulation
   • Attackers might create or escalate accounts via broken validation in membership workflows.
4. Data Enumeration
   • Exposing subscriber information or personal data due to inappropriate endpoint access.
5. Chained Exploits Leading to Full Compromise
   • Initial access via this vulnerability can facilitate deployment of malware or takeover via chaining with other flaws.

Immediate Steps for Site Owners

1. Identify Impacted Sites
   • Audit your WordPress sites to confirm if the vulnerable plugin version is installed. Use the admin plugin page or WP-CLI command:

     wp plugin list | grep subscriptions-memberships-for-paypal

   • Focus on critical or eCommerce sites prioritizing risk reduction.
2. Update Plugin Immediately
   • Upgrade to version 1.1.8 on production sites after testing in staging environments.
   • Verify payment flows and subscription functionality post-update.
3. Create Full Backups
   • Ensure full offsite backups of files and databases before applying updates.
4. If Immediate Update Isn’t Feasible
   • Consider temporarily disabling the plugin if subscriptions are non-essential.
   • Implement WAF virtual patching rules blocking exploit attempts (sample rules provided later).
   • Put your site in maintenance mode during remediation windows.
5. Security Monitoring & Hardening
   • Enable audit logging for admin and subscription-related actions.
   • Monitor logs for abnormal POST requests and subscription status changes.
   • Rotate PayPal API credentials if suspicious activity is detected.
6. Post-Update Validation
   • Confirm that integrations with PayPal Sandbox and subscription workflows function without errors.

How Managed-WP Protects Your Site

As a specialized WordPress security service, Managed-WP offers layered defenses including:

1. Managed WAF with Virtual Patching
   • Preconfigured rules block exploit attempts at the network edge, buying you time when immediate plugin updates aren’t possible.
2. Adaptive Threat Detection
   • Incorporates IP reputation, rate limiting, and behavioral analytics to counter automated scanning and exploit patterns.
3. Regular Malware Scanning
   • Detects unauthorized files or webshell installations that may result from exploitation attempts.
4. Automated and Expert Remediation
   • Premium tiers provide automatic cleanup and expert incident response when threats are detected.
5. Comprehensive Logging and Support
   • Actionable logs and priority remediation help navigate incidents swiftly.

Sample WAF / ModSecurity Rules for Virtual Patching

Apply these sample ModSecurity rules carefully after testing in your staging environment. Replace PLUGIN_ACTION_NAME with specific plugin action names discovered via plugin code or observed traffic.

1) Block unauthenticated POST requests to AJAX actions:

SecRule REQUEST_METHOD "POST" "chain, id:1001001,phase:1,deny,log,msg:'Block unauthenticated POST to plugin AJAX action'"
  SecRule REQUEST_URI "@contains admin-ajax.php" "chain"
  SecRule ARGS:action "@rx (PLUGIN_ACTION_NAME|another_action)" "chain"
  SecRule &REQUEST_COOKIES:wordpress_logged_in -eq 0

2) Prevent state-changing GET requests to plugin endpoints:

SecRule REQUEST_METHOD "GET" "chain,id:1001002,phase:1,deny,log,msg:'Block state-changing GET to plugin endpoint'"
  SecRule REQUEST_URI "@rx /wp-content/plugins/subscriptions-memberships-for-paypal/.*(endpoint-file.php|rest-route)" "t:none"

3) Rate limit suspicious probing:

SecRule REQUEST_URI "@contains admin-ajax.php" "chain,id:1001003,phase:1,pass,nolog"
  SecAction "deny,expirevar:ip.attack_count=60,initcol:ip=%{REMOTE_ADDR}"

4) Block POST requests without valid referer header (optional):

SecRule REQUEST_METHOD "POST" "chain,id:1001004,phase:1,deny,log,msg:'Block POST to plugin endpoint without referer'"
  SecRule REQUEST_URI "@rx /wp-content/plugins/subscriptions-memberships-for-paypal/.*" "chain"
  SecRule REQUEST_HEADERS:Referer "!@rx ^https?://(yourdomain\.com|www\.yourdomain\.com)/"

Disclaimer: Adjust rules to match your environment and plugin details. Always test to minimize false positives. Contact Managed-WP for assistance incorporating these protections.

Detecting Exploitation Attempts

Watch for these indicators in logs and system behavior:

• Unexpected POST requests to admin-ajax.php or plugin REST endpoints from unknown IPs.
• High volume or abnormal frequency of requests targeting plugin functions.
• Subscription status changes without corresponding user activity.
• Creation of new user accounts or privilege escalations during unusual timeframes.
• Unexpected files appearing in uploads, plugin folders, or site root.
• Inconsistent PayPal transaction logs or refuted refunds/payments.
• Server logs showing references lacking legitimate referer headers or originating from suspicious networks.

To investigate, grep server logs for plugin endpoint strings and POST actions and audit user and plugin behavior logs.

Development Best Practices: Preventing Broken Access Control

1. Enforce Capability Checks
   • Use current_user_can() for all admin operations, not relying on client-side info.
2. Nonce Verification
   • Implement wp_nonce_field() and wp_verify_nonce() in forms and AJAX calls.
3. REST API Permissions Callback
   • Ensure REST endpoints specify permission_callback functions validating user rights.
4. Apply Least Privilege Principle
   • Limit backend actions to minimal required capabilities.
5. Input Validation & Sanitization
   • Never trust client inputs when changing server state.
6. Default to Deny Access
   • New endpoints should deny access unless explicitly authorized.
7. Implement Automated Tests
   • Add unit/integration tests for permission enforcement.
8. Conduct Periodic Security Audits
   • Review permissions logic before major releases.

Patch Management Checklist

• Inventory affected sites and plugin versions.
• Create full system backups (files + database).
• Update plugin to version 1.1.8 or newer.
• Test critical subscription and payment flows.
• Implement hardening: strong passwords, MFA, limited admin users.
• Enable and monitor logs of sensitive plugin endpoint access.
• Run malware scans after updates.

Logging and Evidence Collection

If you escalate to incident response, collect:

• Web server logs covering suspicious timeframe.
• WordPress debug logs (wp_debug_log).
• Plugin change histories and audit logs.
• Database snapshots of users and subscriptions.
• Suspicious file copies from uploads or plugin directories.

Preserve timestamps and avoid destructive cleanup before evidence collection.

Long-Term Hardening & Best Practices

1. Keep WordPress core, plugins, and themes consistently updated.
2. Limit administrative roles and adhere to least privilege principle.
3. Segregate high-value sites (eCommerce and memberships) into hardened hosting environments.
4. Deploy managed WAF services with seamless virtual patching capabilities.
5. Subscribe to vulnerability alert feeds for prompt awareness.
6. Maintain an incident response plan with clear steps and backups.

On Responsible Vulnerability Disclosure

Responsible disclosure is vital to a secure WordPress ecosystem. Researchers file issues in good faith; vendors patch accordingly. Site administrators should monitor vulnerability databases and alert services to receive timely update notices for plugins in use.

Incident Response Playbook (Quick 30-60 Minute Checklist)

1. Detect suspicious activity via logs and malware scans.
2. Isolate affected sites—set maintenance mode or disable the plugin temporarily.
3. Create forensic backups (logs, database snapshots).
4. Patch the plugin to version 1.1.8 immediately.
5. Validate payment and user workflows post-update.
6. Rotate API keys and integration secrets if compromise suspected.
7. Clean suspicious files and reset compromised accounts.
8. Communicate with stakeholders and customers regarding incident and resolution.

Frequently Asked Questions

Q: Is updating to version 1.1.8 enough?
A: Updating resolves the known vulnerability. However, continue monitoring logs for abnormal activity and maintain security best practices including backups and least privilege access.

Q: Can a WAF replace plugin updates?
A: WAF can mitigate exploit risk temporarily but is not a permanent substitute for patching. Use WAF as an interim safeguard while updating.

Q: Should I disable the plugin if I cannot update immediately?
A: If subscription features are non-essential, disabling temporarily reduces risk. If feature usage is critical, activate WAF protections and monitor closely.

Operational WAF Tuning Recommendations

• Whitelist trusted third-party IPs (such as PayPal) to prevent accidental blocking.
• Enforce strict rate limits on admin functions accessible externally.
• Apply IP reputation filtering to block known malicious actors.
• Regularly review logs of blocked attempts and tune rules to minimize false positives.
• Use anomaly detection to identify spikes in suspicious POSTs or missing nonce verifications.

Essential Security Actions from Managed-WP

1. Audit your environment for the vulnerable plugin and version.
2. Promptly update to version 1.1.8 or higher.
3. If you delay updates, consult your WAF provider or Managed-WP to apply virtual patches blocking unauthenticated calls.
4. Scan for signs of exploitation and follow incident response steps as needed.
5. Maintain hardened administrator access and vigilance on subscription/payment logs.

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