CVE-2021-24828 in Loan Calculator Plugin
Summary
by MITRE • 01/03/2022
The Mortgage Calculator / Loan Calculator WordPress plugin before 1.5.17 does not escape the some of the attributes of its mlcalc shortcode before outputting them, which could allow users with a role as low as contributor to perform Cross-Site Scripting attacks
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Analysis
by VulDB Data Team • 01/06/2022
The vulnerability identified as CVE-2021-24828 affects the Mortgage Calculator and Loan Calculator WordPress plugin versions prior to 1.5.17, representing a critical cross-site scripting weakness that undermines web application security. This issue stems from insufficient output escaping mechanisms within the plugin's mlcalc shortcode implementation, creating an avenue for malicious actors to inject harmful scripts into web pages viewed by other users. The vulnerability's severity is amplified by the fact that it can be exploited by users with relatively low privileges, specifically contributors who typically have limited capabilities within WordPress environments.
The technical flaw manifests in the plugin's failure to properly sanitize and escape shortcode attributes before rendering them in HTML output contexts. When the mlcalc shortcode processes user-provided parameters, it directly incorporates these values into the generated markup without appropriate escaping procedures. This omission creates a classic XSS vector where malicious input can be executed in the browser context of unsuspecting visitors. The vulnerability specifically targets the handling of certain shortcode attributes that are processed through the plugin's rendering logic, allowing attackers to inject JavaScript code that executes in the victim's browser session.
Operational impact of this vulnerability extends beyond simple script execution as it enables attackers to manipulate the plugin's functionality and potentially compromise user data. Contributors with access to the WordPress admin interface can leverage this vulnerability to inject malicious scripts that could steal cookies, redirect users to malicious sites, or perform actions on behalf of authenticated users. The attack surface is particularly concerning given that contributors often have access to various content management features, making this a potential stepping stone for more extensive privilege escalation attacks. The vulnerability affects all users who interact with pages containing the affected shortcode, potentially exposing thousands of WordPress sites to automated exploitation.
Mitigation strategies for CVE-2021-24828 primarily involve immediate plugin updates to version 1.5.17 or later, which contain the necessary escaping mechanisms to prevent XSS exploitation. System administrators should implement comprehensive monitoring for any suspicious activity related to contributor accounts and shortcode usage, as well as conduct thorough security audits of all installed plugins. The vulnerability aligns with CWE-79, which specifically addresses cross-site scripting flaws in web applications, and demonstrates characteristics consistent with ATT&CK technique T1566, focusing on the initial access phase through malicious web content. Organizations should also consider implementing Content Security Policies and input validation measures as additional defensive layers, while ensuring that contributor accounts maintain minimal necessary permissions to reduce potential exploitation impact.