CVE-2021-24976 in Smart SEO Tool Plugin
Summary
by MITRE • 01/24/2022
The Smart SEO Tool WordPress plugin before 3.0.6 does not sanitise and escape the search parameter before outputting it back in an attribute when the TDK optimisation setting is enabled, leading to a Reflected Cross-Site Scripting
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Analysis
by VulDB Data Team • 01/27/2022
The Smart SEO Tool WordPress plugin vulnerability CVE-2021-24976 represents a critical reflected cross-site scripting flaw that affects versions prior to 3.0.6. This vulnerability exists within the plugin's handling of user input when the TDK optimization setting is enabled, creating a pathway for malicious actors to inject arbitrary JavaScript code into web pages. The issue stems from insufficient sanitization and escaping of the search parameter before it is rendered back into HTML attributes, making it particularly dangerous in web applications where user input is processed and displayed without proper validation.
The technical implementation of this vulnerability involves the plugin's failure to properly sanitize user-supplied data through the search parameter that flows through the TDK optimization functionality. When users perform searches within the WordPress admin interface or frontend areas where this plugin operates, the search term is processed and subsequently reflected back into HTML attributes without adequate escaping mechanisms. This creates a classic reflected XSS vector where an attacker can craft malicious URLs containing script payloads that execute in the context of other users' browsers. The vulnerability is classified under CWE-79 as a failure to sanitize user input, specifically manifesting as reflected cross-site scripting that can be exploited through web browsers.
The operational impact of this vulnerability extends beyond simple script execution, as it can be leveraged for various malicious activities including session hijacking, credential theft, and redirection to malicious sites. Attackers can craft phishing URLs that, when clicked by authenticated users with sufficient privileges, could execute malicious scripts that steal cookies, modify content, or redirect users to harmful destinations. The reflected nature of this vulnerability means that the attack payload is reflected off the web server rather than being stored, making it particularly difficult to detect and prevent through traditional security measures. This vulnerability directly maps to ATT&CK technique T1566.001 for Phishing and T1584.002 for Compromise of Third-Party Applications, as it exploits a weakness in a commonly used WordPress plugin to gain unauthorized access to user sessions.
Mitigation strategies for CVE-2021-24976 should prioritize immediate patching of the Smart SEO Tool plugin to version 3.0.6 or later, which contains the necessary sanitization and escaping fixes. Organizations should also implement additional security measures including input validation at multiple layers, content security policies to restrict script execution, and regular security audits of WordPress plugins to identify similar vulnerabilities. Network-based protections such as web application firewalls can provide additional defense-in-depth, though they should not be relied upon as the sole mitigation strategy. Regular monitoring of plugin repositories and security advisories is essential for maintaining awareness of similar vulnerabilities in other WordPress plugins that may present similar sanitization issues. The vulnerability demonstrates the critical importance of proper input sanitization and output escaping in web applications, particularly when dealing with user-supplied data that may be reflected back to users in HTML contexts.