CVE-2021-24232 in Advanced Booking Calendar Plugin
Summary
by MITRE • 04/23/2021
The Advanced Booking Calendar WordPress plugin before 1.6.8 does not sanitise the license error message when output in the settings page, leading to an authenticated reflected Cross-Site Scripting issue
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Analysis
by VulDB Data Team • 04/27/2021
The Advanced Booking Calendar WordPress plugin vulnerability CVE-2021-24232 represents a critical security flaw that affects versions prior to 1.6.8. This vulnerability resides within the plugin's handling of license error messages on the settings page, where insufficient sanitization allows malicious actors to inject malicious scripts. The flaw specifically manifests as an authenticated reflected cross-site scripting vulnerability that requires user authentication to exploit, making it particularly dangerous in environments where administrative privileges are compromised. The vulnerability falls under the CWE-79 category of Cross-Site Scripting, which is classified as a common weakness in web applications that allows attackers to execute malicious scripts in the context of a victim's browser.
The technical implementation of this vulnerability occurs when the plugin processes license validation errors and directly outputs these messages without proper sanitization or encoding. When an authenticated user accesses the plugin settings page, any maliciously crafted license error message containing script tags or other malicious code can be reflected back to the user's browser, executing the injected scripts in the context of the victim's session. This reflected XSS vulnerability is particularly concerning because it leverages legitimate plugin functionality to deliver malicious payloads, making detection more challenging for security monitoring systems. The authenticated nature of the vulnerability means that an attacker must first obtain valid user credentials, but once achieved, the impact can be significant as the malicious scripts can execute with the privileges of the authenticated user.
The operational impact of this vulnerability extends beyond simple script execution, as it can enable attackers to perform various malicious activities including session hijacking, data exfiltration, and privilege escalation within the WordPress environment. An attacker could potentially steal administrator cookies, modify plugin settings, or redirect users to malicious sites. The vulnerability affects the entire WordPress ecosystem where the Advanced Booking Calendar plugin is installed, potentially compromising multiple sites if administrators are logged in and visit the affected settings page. This type of vulnerability is particularly dangerous in enterprise environments where WordPress installations may be managed by multiple administrators, as a single compromised account could lead to widespread exploitation across the organization. The ATT&CK framework categorizes this as a web application vulnerability that can be leveraged for initial access or privilege escalation, with the reflected XSS serving as a potential vector for more sophisticated attacks.
Mitigation strategies for CVE-2021-24232 primarily involve updating the Advanced Booking Calendar plugin to version 1.6.8 or later, which includes proper sanitization of license error messages. Organizations should also implement comprehensive security monitoring to detect unauthorized access attempts and ensure that administrative accounts maintain strong authentication practices including multi-factor authentication. Input validation and output encoding should be enforced throughout the WordPress environment to prevent similar vulnerabilities from occurring in other plugins or custom code. Security administrators should conduct regular vulnerability assessments of WordPress plugins and maintain updated security policies that address the specific risks associated with authenticated XSS vulnerabilities in content management systems. Additionally, implementing web application firewalls and security headers can provide additional layers of protection against exploitation attempts.