CVE-2021-24436 in W3 Total Cache Plugin
Summary
by MITRE • 07/19/2021
The W3 Total Cache WordPress plugin before 2.1.4 was vulnerable to a reflected Cross-Site Scripting (XSS) security vulnerability within the "extension" parameter in the Extensions dashboard, which is output in an attribute without being escaped first. This could allow an attacker, who can convince an authenticated admin into clicking a link, to run malicious JavaScript within the user's web browser, which could lead to full site compromise.
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Analysis
by VulDB Data Team • 07/22/2021
The CVE-2021-24436 vulnerability affects the W3 Total Cache WordPress plugin version 2.1.3 and earlier, representing a critical reflected cross-site scripting flaw that exploits improper input sanitization within the plugin's Extensions dashboard functionality. This vulnerability resides in the handling of the "extension" parameter where user-supplied input is directly incorporated into HTML attributes without adequate escaping or sanitization measures. The flaw specifically manifests when an authenticated administrator accesses a maliciously crafted URL containing malicious script within the extension parameter, creating a pathway for attackers to execute arbitrary JavaScript code within the victim's browser context.
The technical nature of this vulnerability aligns with CWE-79, which categorizes cross-site scripting flaws as weaknesses in input validation and output encoding. The vulnerability operates through a reflected XSS vector where an attacker crafts a malicious URL containing script payloads and delivers it to a privileged administrator through social engineering techniques. When the administrator clicks the malicious link while logged into the WordPress admin interface, the script executes within the context of the admin's browser session, leveraging the administrator's elevated privileges to perform actions that would otherwise be restricted. The vulnerability's impact is particularly severe because it targets authenticated users with administrative capabilities, providing attackers with direct access to the plugin's administrative functions and potentially enabling complete site compromise.
The operational implications of this vulnerability extend beyond simple script execution, as it creates a persistent attack vector that can be exploited repeatedly against any authenticated administrator who visits the malicious link. Attackers can leverage this vulnerability to steal session cookies, modify plugin configurations, inject malicious content into the website, or even establish backdoor access through the compromised administrative session. The reflected nature of the vulnerability means that the malicious payload is not stored on the server but rather reflected back to the user through the web application's response, making detection more challenging for traditional security monitoring systems. This vulnerability directly maps to ATT&CK technique T1566, specifically targeting the 'Phishing' and 'Spearphishing via Social Media' tactics, as it relies on convincing administrators to click malicious links.
Mitigation strategies for CVE-2021-24436 primarily involve immediate patching to version 2.1.4 or later, which implements proper input sanitization and output escaping for the affected parameter. Administrators should also implement additional security measures including regular security audits of installed plugins, monitoring for suspicious administrative activity, and implementing web application firewalls to detect and block malicious payloads. The vulnerability highlights the importance of input validation and output encoding practices as outlined in OWASP Top Ten and the principle of least privilege in plugin management. Organizations should also consider implementing multi-factor authentication for administrative accounts and regular security training for administrators to reduce the risk of successful social engineering attacks that exploit such vulnerabilities.