CVE-2021-36833 in MC4WP Plugin
Summary
by MITRE • 05/21/2022
Authenticated (admin or higher user role) Stored Cross-Site Scripting (XSS) vulnerability in ibericode's MC4WP plugin <= 4.8.6 at WordPress.
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Analysis
by VulDB Data Team • 01/20/2026
The authenticated stored cross-site scripting vulnerability identified as CVE-2021-36833 resides within the MC4WP plugin for WordPress, affecting versions up to and including 4.8.6. This vulnerability specifically targets users with administrator or higher privileges, making it particularly dangerous in environments where administrative access is compromised. The issue stems from insufficient input validation and output sanitization within the plugin's handling of user-supplied data, creating an avenue for persistent malicious script injection that can affect all users interacting with the compromised WordPress installation.
The technical flaw manifests in the plugin's failure to properly sanitize user input before storing and subsequently rendering it within web pages. When administrators or privileged users interact with the plugin's administrative interfaces, malicious scripts can be stored in the database and executed whenever other users view affected pages. This stored XSS vulnerability operates under CWE-79 which categorizes improper neutralization of input during web page generation, specifically targeting the failure to sanitize data that flows from user inputs to web outputs. The vulnerability enables attackers to execute arbitrary JavaScript code within the context of the victim's browser, potentially leading to session hijacking, credential theft, or further exploitation of the compromised WordPress environment.
The operational impact of this vulnerability extends beyond simple script execution, as it provides attackers with persistent access to the WordPress administration interface and potentially full system compromise. An attacker with administrator privileges can inject malicious scripts that persist across user sessions, allowing for continuous monitoring, data exfiltration, or privilege escalation within the WordPress environment. The vulnerability aligns with ATT&CK technique T1566.001 which covers the use of malicious file content in phishing attacks, as the stored XSS can be leveraged to deliver malicious payloads that exploit other vulnerabilities within the WordPress ecosystem. This persistent nature makes the vulnerability particularly attractive to threat actors seeking long-term access to compromised systems.
Mitigation strategies for CVE-2021-36833 should prioritize immediate plugin updates to versions 4.8.7 or later, which contain the necessary security patches addressing the XSS vulnerability. Administrators should also implement comprehensive input validation and output encoding mechanisms within their WordPress environments, ensuring that all user-supplied data undergoes proper sanitization before database storage. Network-based security controls including web application firewalls should be configured to detect and block suspicious script patterns, while regular security audits should verify that no malicious scripts have been previously injected into the system. Additionally, implementing principle of least privilege access controls and regular security monitoring can help detect unauthorized modifications to plugin configurations or user accounts that might indicate exploitation attempts.