CVE-2025-13079: WordPress Popup Builder Auth Bypass Flaw

CVE-2025-13079 Overview

The Popup Builder plugin for WordPress, a widely-used marketing popup solution, contains an authorization bypass vulnerability in all versions up to and including 4.4.2. The vulnerability stems from the plugin's use of predictable unsubscribe tokens generated from deterministic data, enabling unauthenticated attackers to forcibly unsubscribe arbitrary users from mailing lists.

Critical Impact

Unauthenticated attackers can unsubscribe legitimate subscribers from mailing lists by brute-forcing predictable tokens, disrupting email marketing campaigns and potentially causing significant business impact.

Affected Products

• Popup Builder WordPress Plugin versions up to and including 4.4.2
• WordPress sites utilizing Popup Builder's mailing list functionality
• Email subscription systems integrated with affected Popup Builder versions

Discovery Timeline

• 2026-02-19 - CVE CVE-2025-13079 published to NVD
• 2026-02-19 - Last updated in NVD database

Technical Details for CVE-2025-13079

Vulnerability Analysis

This vulnerability is classified under CWE-1241 (Use of Predictable Algorithm in Random Number Generator), which highlights the fundamental weakness in how the Popup Builder plugin generates unsubscribe tokens. Rather than using cryptographically secure random values, the plugin constructs tokens from deterministic data that can be predicted or brute-forced by attackers.

The vulnerability resides within the Actions.php and AdminHelper.php files of the Popup Builder plugin. When a subscriber is added to a mailing list, the plugin generates an unsubscribe token that allows them to opt out of future communications. However, because this token is derived from predictable inputs rather than secure random generation, attackers who know a victim's email address can systematically attempt to guess valid tokens.

The network-accessible nature of this vulnerability means no authentication is required for exploitation, and the attack can be executed remotely against any WordPress site running the vulnerable plugin version.

Root Cause

The root cause lies in the plugin's token generation algorithm within AdminHelper.php at line 896. Instead of implementing cryptographically secure random token generation (such as using random_bytes() or wp_generate_password() with appropriate entropy), the plugin uses deterministic data inputs that can be reverse-engineered or brute-forced. This predictability violates secure coding practices for token generation, where tokens must be sufficiently random to prevent enumeration attacks.

Attack Vector

The attack requires the following conditions:

1. The attacker must know the victim's email address that is subscribed to the mailing list
2. The attacker must have network access to the target WordPress site
3. The attacker systematically brute-forces the unsubscribe endpoint with generated token candidates

Once a valid token is discovered, the attacker can unsubscribe the victim without their consent, effectively removing them from marketing communications. While this does not compromise confidentiality, it impacts the integrity of the subscriber database and can disrupt business operations dependent on email marketing.

The exploitation mechanics involve sending HTTP requests to the unsubscribe endpoint with candidate tokens until a match is found. The feasibility depends on the token space and rate limiting controls, which may be insufficient in default configurations.

Detection Methods for CVE-2025-13079

Indicators of Compromise

• Unusual spikes in unsubscribe requests from single IP addresses
• Multiple failed unsubscribe attempts with incremental or patterned token values
• Unexpected subscriber churn from mailing lists without corresponding user actions
• HTTP requests to unsubscribe endpoints with automated request patterns

Detection Strategies

• Monitor web server logs for repeated requests to Popup Builder unsubscribe endpoints containing varying token parameters
• Implement rate limiting detection for the unsubscribe functionality to identify brute-force attempts
• Audit subscriber lists for unexplained unsubscription events, particularly affecting high-value contacts
• Deploy Web Application Firewall (WAF) rules to detect token enumeration patterns

Monitoring Recommendations

• Enable detailed logging for the Popup Builder plugin's subscription management functions
• Configure alerts for abnormal unsubscribe activity thresholds within defined time windows
• Integrate WordPress security plugins that provide real-time threat detection and logging capabilities
• Review the Wordfence Vulnerability Report for updated threat intelligence

How to Mitigate CVE-2025-13079

Immediate Actions Required

• Update Popup Builder plugin to a version newer than 4.4.2 that addresses this vulnerability
• Audit current subscriber lists for suspicious unsubscription activity
• Implement rate limiting on unsubscribe endpoints at the web server or WAF level
• Consider temporarily disabling automated unsubscribe functionality until patched

Patch Information

The vulnerability has been addressed in versions released after 4.4.2. Administrators should update to the latest available version through the WordPress plugin repository. The WordPress Popup Builder Changeset contains the security fix details. Site administrators can verify vulnerable code patterns by reviewing the Actions.php and AdminHelper.php files in the affected version.

Workarounds

• Implement server-level rate limiting on requests to unsubscribe endpoints (e.g., limit to 5 requests per minute per IP)
• Deploy a Web Application Firewall rule to detect and block rapid sequential requests with varying token parameters
• Add CAPTCHA verification to the unsubscribe process to prevent automated brute-force attacks
• Consider implementing email confirmation for unsubscribe requests as an additional verification layer

# Example nginx rate limiting configuration for unsubscribe endpoint
limit_req_zone $binary_remote_addr zone=unsubscribe_limit:10m rate=5r/m;

location ~ /wp-content/plugins/popup-builder/ {
    limit_req zone=unsubscribe_limit burst=3 nodelay;
    # Additional security headers
    add_header X-Content-Type-Options nosniff;
    add_header X-Frame-Options DENY;
}