CVE-2019-16524 in easy-fancybox Plugin
Summary
by MITRE
The easy-fancybox plugin before 1.8.18 for WordPress (aka Easy FancyBox) is susceptible to Stored XSS in the Settings Menu inc/class-easyfancybox.php due to improper encoding of arbitrarily submitted settings parameters. This occurs because there is no inline styles output filter.
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Analysis
by VulDB Data Team • 09/10/2020
The vulnerability identified as CVE-2019-16524 affects the easy-fancybox WordPress plugin version 1.8.17 and earlier, representing a critical stored cross-site scripting flaw that compromises user sessions and system integrity. This vulnerability exists within the plugin's settings management interface where user-submitted parameters are not properly sanitized or encoded before being stored and subsequently rendered back to users. The specific file inc/class-easyfancybox.php contains the flaw where inline styles are output without adequate filtering mechanisms, creating an environment where malicious actors can inject harmful scripts that persist across user sessions. The vulnerability operates at the intersection of web application security and user input handling, where the absence of proper output encoding creates a persistent threat vector.
The technical exploitation of this vulnerability occurs when an authenticated administrator or user with sufficient privileges accesses the plugin's settings menu and submits malicious input containing script tags or other harmful code. The plugin's failure to implement proper HTML encoding or sanitization functions means that these malicious inputs are stored directly in the database and later executed when other users view the settings page. This stored XSS vulnerability allows attackers to execute arbitrary JavaScript code within the context of the victim's browser, potentially leading to session hijacking, privilege escalation, or data exfiltration. The vulnerability aligns with CWE-79 which specifically addresses cross-site scripting flaws, and represents a classic case of improper output escaping in web applications. The lack of inline styles output filter creates a direct pathway for malicious code execution, as the plugin fails to properly escape user-controllable data before rendering it in HTML contexts.
The operational impact of this vulnerability extends beyond simple script execution to encompass potential complete system compromise through session hijacking and privilege escalation. An attacker who successfully exploits this vulnerability can gain persistent access to the WordPress administration interface, potentially modifying plugin settings, uploading malicious files, or creating new administrator accounts. The stored nature of the vulnerability means that the malicious code executes automatically for any user who views the affected settings page, making it particularly dangerous for high-privilege accounts. This vulnerability also enables social engineering attacks where attackers can manipulate the plugin settings to redirect users to malicious domains or inject malicious content that appears legitimate. The impact is exacerbated by the fact that WordPress administrators often have elevated privileges, making successful exploitation potentially devastating to the entire website infrastructure and its associated data.
Mitigation strategies for CVE-2019-16524 should include immediate patching to version 1.8.18 or later where the plugin properly implements output encoding for settings parameters. Organizations should implement network monitoring to detect potential exploitation attempts and establish robust input validation procedures for all user-controllable parameters. The recommended approach aligns with ATT&CK technique T1059.007 for command and scripting interpreter and T1566.001 for credential access through social engineering. Security teams should also implement regular security audits of WordPress plugins, maintain up-to-date vulnerability databases, and establish incident response procedures specifically addressing stored XSS vulnerabilities. Additionally, administrators should consider implementing content security policies and regular security scanning of plugin files to detect unauthorized modifications. The vulnerability highlights the critical importance of proper output encoding in web applications and demonstrates how seemingly minor implementation flaws can create significant security risks when combined with administrative access privileges.