CVE-2021-24535 in Light Messages Plugin
Summary
by MITRE • 08/16/2021
The Light Messages WordPress plugin through 1.0 is lacking CSRF check when updating it's settings, and is not sanitising its Message Content in them (even with the unfiltered_html disallowed). As a result, an attacker could make a logged in admin update the settings to arbitrary values, and set a Cross-Site Scripting payload in the Message Content. Depending on the options set, the XSS payload can be triggered either in the backend only (in the plugin's settings), or both frontend and backend.
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Analysis
by VulDB Data Team • 08/18/2021
The vulnerability identified as CVE-2021-24535 affects the Light Messages WordPress plugin version 1.0 and earlier, presenting a critical security risk through the absence of Cross-Site Request Forgery protection mechanisms during administrative settings updates. This flaw creates a pathway for authenticated attackers to manipulate plugin configurations without proper authorization, exploiting the plugin's insufficient validation and sanitization processes. The vulnerability resides in the plugin's failure to implement proper CSRF token verification, allowing malicious actors to craft requests that appear legitimate to the WordPress administration interface.
The technical implementation of this vulnerability stems from the plugin's improper handling of user input within its settings management system. Specifically, when administrators modify plugin configurations, the system does not validate the authenticity of the request through CSRF protection measures, enabling attackers to submit malicious requests that bypass normal administrative controls. Additionally, the plugin demonstrates inadequate sanitization of message content fields, even when the WordPress environment restricts unfiltered_html capabilities. This dual failure creates a scenario where attackers can inject malicious JavaScript code into the message content fields, which then executes when the content is rendered within the plugin's interface.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it creates a persistent cross-site scripting vector that can affect both frontend and backend interfaces depending on plugin configuration. When executed, the XSS payload can compromise administrator sessions, steal sensitive cookies, redirect users to malicious sites, or enable further exploitation of the compromised WordPress installation. The vulnerability's reach is amplified because it affects the administrative backend where the payload executes, potentially allowing attackers to gain deeper access to the WordPress system, modify content, or even install malware. The reflected nature of the XSS means that the malicious code can be triggered whenever the affected settings page is accessed, making it particularly dangerous for administrators who regularly manage plugin configurations.
Security mitigations for this vulnerability should focus on implementing comprehensive CSRF protection mechanisms within the plugin's administrative interfaces, ensuring that all configuration updates require valid authentication tokens before processing. The plugin must also enforce strict input sanitization of all user-provided content, including message fields, regardless of WordPress's unfiltered_html restrictions. Organizations should immediately update to patched versions of the Light Messages plugin, disable the plugin if updates are not immediately available, and conduct thorough security audits of their WordPress installations to identify similar vulnerabilities in other third-party plugins. This vulnerability aligns with CWE-352, which specifically addresses Cross-Site Request Forgery, and maps to ATT&CK technique T1059.007 for script injection, highlighting the need for robust input validation and authentication controls in web applications.
The exploitation of this vulnerability demonstrates the critical importance of proper security controls in content management systems, particularly regarding administrative interfaces and user input handling. WordPress plugin developers must implement comprehensive security measures including CSRF protection, proper input validation, and output sanitization to prevent similar issues. Organizations should maintain updated security practices including regular plugin audits, monitoring for known vulnerabilities, and implementing security headers to mitigate the impact of XSS attacks. The vulnerability serves as a reminder that even seemingly simple plugins can present significant security risks when proper security controls are not implemented, emphasizing the need for security-by-design principles in all web application development processes.