CVE-2021-24670 in CoolClock Plugin
Summary
by MITRE • 09/28/2021
The CoolClock WordPress plugin before 4.3.5 does not escape some shortcode attributes, allowing users with a role as low as Contributor toperform Stored Cross-Site Scripting attacks
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Analysis
by VulDB Data Team • 10/03/2021
The CoolClock WordPress plugin vulnerability CVE-2021-24670 represents a critical stored cross-site scripting flaw that affects versions prior to 4.3.5. This vulnerability specifically targets the plugin's handling of shortcode attributes without proper output escaping mechanisms. The flaw allows threat actors with minimal privileges to execute malicious scripts within the context of affected websites, making it particularly dangerous for WordPress environments where contributor-level users have access to the administration interface. The vulnerability stems from insufficient sanitization of user-provided input within the plugin's shortcode processing functionality, creating an attack vector that can persist across multiple user sessions.
The technical implementation of this vulnerability involves the plugin's failure to properly escape shortcode attributes when rendering clock displays on web pages. When contributors or users with similar privileges create or modify posts containing CoolClock shortcodes with malicious attribute values, the plugin stores these unescaped inputs directly into the database. Subsequently, when other users view pages containing these stored shortcodes, the malicious scripts execute in their browsers, potentially leading to session hijacking, data theft, or further compromise of the WordPress installation. This stored XSS vulnerability operates under CWE-79 which specifically addresses cross-site scripting flaws in web applications. The attack chain typically follows the pattern of initial privilege escalation through contributor accounts, followed by payload injection into shortcode parameters, and finally execution against unsuspecting end users.
The operational impact of CVE-2021-24670 extends beyond simple script execution as it can enable attackers to perform sophisticated attacks leveraging the ATT&CK framework's credential access and persistence techniques. An attacker with contributor privileges can craft malicious shortcodes that, when viewed by administrators or other users, can steal cookies, redirect users to malicious sites, or even establish backdoors through browser-based exploitation. The vulnerability's persistence characteristic means that once exploited, the malicious code remains active until the plugin is updated or the affected shortcode content is manually removed. This makes the vulnerability particularly dangerous in multi-user environments where multiple contributors might be working on the same site, as the attack can spread through content creation activities. The low privilege requirement significantly increases the attack surface, as many WordPress installations have numerous contributor accounts for content management purposes.
Mitigation strategies for CVE-2021-24670 should focus on immediate plugin updates to version 4.3.5 or later, which contain proper output escaping mechanisms for shortcode attributes. Administrators should also implement strict content review processes for contributor accounts, particularly when dealing with shortcode-based content creation. Additional protective measures include implementing content security policies that restrict script execution and monitoring for unusual shortcode usage patterns. The vulnerability highlights the importance of proper input validation and output escaping as fundamental security practices, aligning with security standards that recommend sanitizing all user-provided data before storage and rendering. Organizations should also consider implementing web application firewalls to detect and block potential exploitation attempts, while maintaining regular security audits to identify similar vulnerabilities in other plugins or themes that might be present in their WordPress installations.