CVE-2021-24905 in Advanced Contact form 7 DB Plugin
Summary
by MITRE • 03/21/2022
The Advanced Contact form 7 DB WordPress plugin before 1.8.7 does not have authorisation nor CSRF checks in the acf7_db_edit_scr_file_delete AJAX action, and does not validate the file to be deleted, allowing any authenticated user to delete arbitrary files on the web server. For example, removing the wp-config.php allows attackers to trigger WordPress setup again, gain administrator privileges and execute arbitrary code or display arbitrary content to the users.
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Analysis
by VulDB Data Team • 03/23/2022
The Advanced Contact Form 7 DB WordPress plugin vulnerability CVE-2021-24905 represents a critical authorization and validation flaw that undermines the security posture of WordPress installations. This vulnerability exists in plugin versions prior to 1.8.7 and specifically affects the acf7_db_edit_scr_file_delete AJAX action which lacks proper authentication mechanisms and cross-site request forgery protections. The flaw allows any authenticated user to execute arbitrary file deletion operations on the web server, creating a severe privilege escalation vector that can be exploited by attackers with minimal privileges.
The technical implementation of this vulnerability stems from insufficient input validation and authorization checks within the plugin's AJAX handling mechanism. The acf7_db_edit_scr_file_delete endpoint does not perform proper validation of the file paths being submitted for deletion, nor does it verify whether the authenticated user possesses the necessary permissions to perform such operations. This absence of proper access controls creates a path for attackers to manipulate the file deletion process and target critical system files. The vulnerability aligns with CWE-863, which addresses "Incorrect Authorization" in software systems, and represents a clear violation of the principle of least privilege that should govern all system operations.
The operational impact of this vulnerability extends far beyond simple file deletion capabilities, as demonstrated by the specific example of wp-config.php removal. When an attacker can delete the WordPress configuration file, they effectively reset the WordPress installation process, allowing for complete administrative control over the site. This creates a scenario where attackers can reconfigure the system to their advantage, potentially establishing persistent backdoors or executing arbitrary code through the administrative interface. The vulnerability also enables content injection attacks where attackers can manipulate the web server to display malicious content to users, representing a significant threat to both site integrity and user security.
The exploitation of this vulnerability follows a predictable pattern where attackers first authenticate to the WordPress system using any valid user account, then leverage the unauthenticated file deletion functionality to target critical system files. This attack vector is particularly dangerous because it requires minimal privileges to initiate, making it accessible to users with basic authentication access. The attack aligns with ATT&CK technique T1059.001 for command and script injection, as attackers can potentially use the compromised system to execute malicious code. The vulnerability also supports privilege escalation techniques described in ATT&CK matrix under T1078 for valid accounts and T1548.001 for abuse of system privileges.
Mitigation strategies for CVE-2021-24905 require immediate action including updating the Advanced Contact Form 7 DB plugin to version 1.8.7 or later where the authorization and validation issues have been addressed. Organizations should also implement proper file access controls and regularly audit their WordPress plugin installations for known vulnerabilities. Network monitoring should be enhanced to detect unusual file deletion patterns that may indicate exploitation attempts. Additionally, implementing proper input validation and authentication checks at the application level, as well as maintaining updated security patches across all WordPress components, will help prevent similar vulnerabilities from arising in the future. The remediation process should also include reviewing and hardening the WordPress configuration to limit file system access and implementing proper backup procedures to quickly recover from potential file deletion attacks.