CVE-2022-2594 in Advanced Custom Fields Plugin
Summary
by MITRE • 08/22/2022
The Advanced Custom Fields WordPress plugin before 5.12.3, Advanced Custom Fields Pro WordPress plugin before 5.12.3 allows unauthenticated users to upload files allowed in a default WP configuration (so PHP is not possible) if there is a frontend form available. This vulnerability was introduced in the 5.0 rewrite and did not exist prior to that release.
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Analysis
by VulDB Data Team • 08/22/2022
The vulnerability identified as CVE-2022-2594 affects the Advanced Custom Fields WordPress plugin and its Pro variant, specifically versions prior to 5.12.3. This security flaw represents a critical oversight in the plugin's file upload functionality that emerged during the significant 5.0 rewrite implementation. The vulnerability creates an exploitable condition where unauthenticated users can leverage frontend forms to upload files, despite the plugin's intended security controls. The issue is particularly concerning because it operates within the default WordPress configuration where PHP execution is disabled, yet the vulnerability still permits unauthorized file uploads that could potentially be leveraged for malicious purposes.
The technical flaw resides in the plugin's handling of file uploads through frontend forms, where the access control mechanisms fail to properly validate user authentication status. This weakness allows attackers to bypass authentication requirements and submit files through exposed frontend interfaces. The vulnerability was introduced during the 5.0 rewrite, indicating that the security model was fundamentally altered in a way that compromised file upload validation. The affected versions maintain a dangerous state where frontend forms remain accessible to unauthorized users, creating an attack surface that extends beyond the plugin's intended security boundaries.
Operationally, this vulnerability creates a significant risk for WordPress installations using the affected Advanced Custom Fields plugins. Attackers can exploit this weakness to upload various file types through accessible frontend forms, potentially leading to the deployment of malicious scripts or other harmful content. Even though PHP execution is disabled in the default WordPress configuration, the ability to upload other file types such as images, text files, or executable content in other formats could still provide attackers with footholds for further exploitation. The impact extends beyond simple file uploads as this vulnerability could enable attackers to establish persistent access points or deliver additional payloads through the uploaded files.
The vulnerability aligns with CWE-434 which addresses "Unrestricted Upload of File with Dangerous Type" and represents a clear violation of secure coding practices for file handling operations. From an ATT&CK perspective, this vulnerability maps to techniques involving initial access through web application vulnerabilities and potentially privilege escalation through file upload exploitation. Organizations using affected plugin versions face increased risk of compromise, particularly those with frontend forms that accept user uploads. The vulnerability demonstrates the critical importance of proper access control implementation during major software rewrites and highlights the need for comprehensive security testing of modified authentication mechanisms.
Mitigation strategies should focus on immediate plugin updates to versions 5.12.3 or later, which contain the necessary security patches. Administrators should also review and restrict frontend form access where possible, implementing additional authentication layers for file upload functionality. Network monitoring should be enhanced to detect unusual file upload patterns, and regular security audits should verify that all plugin components maintain appropriate access controls. The vulnerability serves as a reminder that even seemingly minor functionality changes during software updates can introduce significant security regressions requiring careful validation and testing before deployment in production environments.