CVE-2021-36841 in YITH Maintenance Mode Plugin
Summary
by MITRE • 09/28/2021
Authenticated Stored Cross-Site Scripting (XSS) vulnerability in YITH Maintenance Mode (WordPress plugin) versions
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Analysis
by VulDB Data Team • 10/02/2021
The CVE-2021-36841 vulnerability represents a critical authenticated stored cross-site scripting flaw discovered in the YITH Maintenance Mode WordPress plugin. This vulnerability affects multiple versions of the plugin and poses significant security risks to WordPress websites that rely on this maintenance mode functionality. The issue stems from insufficient input validation and output sanitization within the plugin's administrative interfaces where user-supplied data is not properly escaped before being stored and subsequently rendered back to users. The vulnerability specifically impacts the plugin's ability to handle malicious script payloads within maintenance mode settings, potentially allowing attackers with valid administrative credentials to inject malicious JavaScript code that executes in the context of other users' browsers.
The technical exploitation of this vulnerability requires an authenticated attacker with administrative privileges to the WordPress site, making it a privilege escalation concern rather than a direct remote code execution vector. However, the impact remains severe as the stored XSS payload can persist in the plugin's configuration storage and execute whenever affected pages are accessed by other authenticated users. The flaw typically occurs when administrators configure maintenance mode messages, custom CSS, or other editable content fields within the plugin's administrative panel, where user input is directly stored without proper sanitization. This vulnerability aligns with CWE-79, which defines cross-site scripting as a common weakness in web applications where untrusted data is incorporated into web pages without proper validation or escaping.
The operational impact of CVE-2021-36841 extends beyond simple data theft or session hijacking, as it can enable more sophisticated attacks including credential harvesting, malware distribution, and privilege escalation within the compromised WordPress environment. Attackers can leverage the stored XSS to steal administrator sessions, inject malicious code that modifies website content, or redirect users to phishing sites that appear legitimate. The persistence of the vulnerability means that once exploited, the malicious scripts remain active until manually removed from the plugin configuration, potentially affecting all users who access the maintenance mode pages. This makes the vulnerability particularly dangerous in environments where multiple administrators have access to the plugin settings, as it can be exploited by any compromised account with sufficient privileges.
Organizations affected by this vulnerability should immediately update to the patched version of the YITH Maintenance Mode plugin, as the vendor has released security updates addressing this specific flaw. Security teams should conduct comprehensive audits of their WordPress installations to identify any other instances of the vulnerable plugin versions and implement monitoring for suspicious administrative activities. The mitigation strategy should include implementing principle of least privilege access controls for WordPress administrative accounts, enabling two-factor authentication, and conducting regular security assessments of third-party plugins. This vulnerability also highlights the importance of proper input validation and output escaping practices, aligning with ATT&CK technique T1211 which covers lateral movement through compromised credentials, and emphasizing the need for web application security controls to prevent persistent XSS vulnerabilities in content management systems.