CVE-2021-24817 in Ultimate NoFollow Plugin
Summary
by MITRE • 12/13/2021
The Ultimate NoFollow WordPress plugin through 1.4.8 does not sanitise and escape the href attribute of its shortcodes, allowing users with a role as low as contributor to perform Cross-Site Scripting attacks
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Analysis
by VulDB Data Team • 12/16/2021
The vulnerability identified as CVE-2021-24817 affects the Ultimate NoFollow WordPress plugin version 1.4.8 and earlier, representing a critical cross-site scripting flaw that undermines the security posture of affected WordPress installations. This vulnerability stems from insufficient input sanitization and output escaping mechanisms within the plugin's shortcode implementation, specifically targeting the href attribute. The flaw is particularly concerning because it allows users with minimal privileges, including contributors who typically have limited capabilities within WordPress, to execute malicious scripts against other users who view content containing the vulnerable shortcodes.
The technical exploitation of this vulnerability occurs through the improper handling of user-supplied input in the plugin's shortcode attributes. When a contributor creates or modifies content containing the Ultimate NoFollow shortcode with malicious href values, the plugin fails to properly sanitize these inputs before rendering them in the browser. This lack of sanitization creates an environment where malicious JavaScript code can be injected into the page and executed in the context of other users' browsers. The vulnerability is classified under CWE-79 as a failure to sanitize user input, specifically manifesting as a cross-site scripting vulnerability that allows attackers to inject client-side scripts.
The operational impact of CVE-2021-24817 extends beyond simple script injection, as it enables attackers to potentially steal session cookies, redirect users to malicious sites, or perform actions on behalf of other users within the WordPress environment. Contributors typically have the ability to create posts and pages, making this vulnerability particularly dangerous as it allows for persistent malicious content injection that can affect all users who view the compromised pages. The vulnerability can be exploited through various attack vectors including blog posts, pages, comments, and custom fields where shortcodes are rendered, creating multiple potential entry points for malicious actors.
Security practitioners should prioritize the immediate mitigation of this vulnerability through plugin updates to version 1.4.9 or later, which contain the necessary sanitization fixes. Additionally, administrators should implement strict content filtering policies and consider role-based access restrictions to limit contributor capabilities where possible. The vulnerability aligns with ATT&CK technique T1548.002 which involves privilege escalation through the exploitation of web application vulnerabilities, and T1203 which covers the use of malicious content in web applications. Organizations should also conduct comprehensive security assessments of their WordPress installations to identify similar vulnerabilities in other plugins, as this represents a common pattern in WordPress security issues where insufficient input validation leads to critical security flaws. The incident underscores the importance of proper input sanitization and output escaping practices as outlined in OWASP Top Ten categories and emphasizes the need for regular security audits of third-party WordPress plugins to maintain overall system integrity.