CVE-2026-5415 in Advanced Google reCAPTCHA Plugin
Summary
by MITRE • 06/05/2026
The WP Captcha PRO (the premium version of the Advanced Google reCAPTCHA plugin, both have the same slug) plugin for WordPress is vulnerable to Authentication Bypass in all versions up to, and including, 5.38. This is due to the ajax_run_tool() AJAX handler relying solely on a nonce check (check_ajax_referer) for security without performing any capability check, combined with the create_temporary_link tool allowing the generation of passwordless login links for arbitrary users, and the handle_temporary_links() function authenticating visitors via these links without any additional authorization validation. The required nonce is exposed to all authenticated backend users (including Subscribers) via wp_localize_script() on all non-settings admin pages when the plugin's welcome pointer has not been dismissed. This makes it possible for authenticated attackers, with Subscriber-level access and above, to bypass normal authentication and log in as any user, including Administrators, resulting in complete account takeover.
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Analysis
by VulDB Data Team • 06/06/2026
The WP Captcha PRO plugin vulnerability represents a critical authentication bypass flaw that undermines the security posture of WordPress installations. This vulnerability affects all versions up to and including 5.38, making it a persistent threat across multiple releases. The flaw stems from a fundamental design oversight in the plugin's AJAX handling mechanism where the ajax_run_tool() function performs only nonce validation without implementing proper capability checks. This architectural weakness creates a pathway for unauthorized access that directly violates security principles of least privilege and proper authentication controls.
The technical exploitation of this vulnerability leverages the create_temporary_link tool which generates passwordless login links for arbitrary users within the system. This functionality becomes dangerous when combined with the handle_temporary_links() function that authenticates visitors based on these temporary links without additional authorization validation. The authentication bypass occurs because the system trusts the temporary links without verifying that the requesting user has legitimate authorization to access the target account. This design flaw enables attackers to escalate privileges through a simple workflow that bypasses normal authentication mechanisms entirely.
The exposure of the required nonce token through wp_localize_script() on all non-settings admin pages creates an additional attack vector that significantly lowers the barrier to exploitation. This nonce is accessible to all authenticated backend users including those with Subscriber-level permissions, effectively providing attackers with the means to craft malicious requests that appear legitimate to the WordPress system. The nonce exposure occurs specifically when the plugin's welcome pointer has not been dismissed, making the vulnerability accessible to any authenticated user who has not completed the initial setup walkthrough. This implementation directly violates security best practices by exposing authentication tokens to users who should not have access to them.
The operational impact of this vulnerability extends beyond simple privilege escalation to encompass complete account takeover scenarios. Attackers with Subscriber-level access or higher can leverage this flaw to log in as any user within the system, including administrators, thereby gaining full control over the WordPress installation. This level of compromise allows for complete data exfiltration, malicious code deployment, and system modification that can persist even after the vulnerability is patched. The vulnerability's severity is further amplified by its ability to affect all authenticated users, making it particularly dangerous in environments where multiple user roles exist and where the plugin's temporary link functionality is actively used.
From a security standards perspective, this vulnerability maps directly to CWE-863, which addresses "Incorrect Authorization" in software systems. The flaw represents a clear violation of authorization principles where the system fails to properly validate that the requesting entity has sufficient privileges to perform the requested action. Additionally, this vulnerability aligns with ATT&CK technique T1078.004, which covers "Valid Accounts: Cloud Accounts" in the context of unauthorized access through legitimate authentication mechanisms. The attack pattern follows a privilege escalation workflow that leverages legitimate system functionality to bypass normal security controls, making it particularly challenging to detect through standard security monitoring.
Mitigation strategies should focus on immediate patching of the plugin to the latest version where the vulnerability has been addressed through proper capability checks and nonce validation. Organizations should also implement network-level restrictions to limit access to administrative interfaces and consider disabling the temporary link functionality if it is not essential for operations. Security monitoring should be enhanced to detect unusual patterns of temporary link generation and authentication attempts, particularly from lower-privilege accounts. Regular security audits of WordPress plugins should include verification of proper capability checks in AJAX handlers and review of nonce exposure practices to prevent similar vulnerabilities from emerging in other components of the WordPress ecosystem.