CVE-2021-4350 in Frontend File Manager Plugin
Summary
by MITRE • 06/07/2023
The Frontend File Manager plugin for WordPress is vulnerable to Unauthenticated HTML Injection in versions up to, and including, 18.2. This is due to lacking authentication protections on the wpfm_send_file_in_email AJAX action. This makes it possible for unauthenticated attackers to send emails using the site with a custom subject, recipient email, and body with unsanitized HTML content. This effectively lets the attacker use the site as a spam relay.
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Analysis
by VulDB Data Team • 07/05/2023
The vulnerability identified as CVE-2021-4350 affects the Frontend File Manager plugin for WordPress, specifically targeting versions up to and including 18.2. This represents a critical security flaw that undermines the integrity of WordPress installations by exposing a critical functionality to unauthorized access. The vulnerability stems from insufficient authentication mechanisms within the plugin's AJAX endpoint, creating a pathway for malicious actors to exploit the system without requiring valid credentials or administrative privileges. The exposed wpfm_send_file_in_email AJAX action serves as the primary attack vector, allowing unauthorized users to manipulate the plugin's email sending capabilities and leverage the vulnerable WordPress site for nefarious activities.
The technical implementation of this vulnerability demonstrates a clear failure in input validation and access control measures. The plugin's AJAX handler lacks proper authentication checks, enabling any user to invoke the email sending functionality regardless of their authentication status. This flaw creates an environment where attackers can craft malicious email payloads containing unsanitized HTML content, which gets processed and transmitted through the vulnerable WordPress installation. The injection occurs at the email composition layer, where the subject line, recipient address, and body content can all be manipulated by unauthenticated users. This type of vulnerability aligns with CWE-352, which addresses Cross-Site Request Forgery (CSRF) conditions where insufficient validation allows unauthorized actions to be performed on behalf of users.
The operational impact of this vulnerability extends far beyond simple email injection, as it transforms the compromised WordPress site into an effective spam relay mechanism. Attackers can utilize the legitimate domain and reputation of the vulnerable website to send spam emails to unsuspecting recipients, potentially leading to the site being blacklisted by email providers and security vendors. The unsanitized HTML content injection capability allows for the delivery of malicious payloads through email attachments or embedded links, creating additional attack vectors beyond simple spam distribution. This vulnerability also poses risks to the site's reputation and can result in legal consequences for the website owner, as the compromised system becomes a tool for distributing unwanted communications. The ease of exploitation means that even automated scanning tools can identify and exploit this vulnerability, making it particularly dangerous for widespread abuse.
Mitigation strategies for this vulnerability must address both immediate remediation and long-term security hardening measures. The most effective immediate solution involves updating the Frontend File Manager plugin to a version that includes proper authentication checks for the wpfm_send_file_in_email AJAX action. Administrators should also implement rate limiting on AJAX endpoints to prevent abuse of the email functionality and consider restricting access to sensitive plugin features through .htaccess rules or firewall configurations. Network-level protections such as implementing email authentication protocols including SPF, DKIM, and DMARC can help mitigate the damage caused by the spam relay functionality. Additionally, monitoring for unusual email sending patterns and implementing proper input sanitization for all user-provided content can serve as additional defensive measures. This vulnerability highlights the importance of following the principle of least privilege and implementing proper authentication controls for all application endpoints, as outlined in the ATT&CK framework's privilege escalation and command and control techniques. Organizations should also conduct regular security assessments of their WordPress plugins to identify similar vulnerabilities that could be exploited to compromise their systems and maintain the security posture of their web applications.