CVE-2022-4670 in PDF.js Viewer Plugin
Summary
by MITRE • 02/06/2023
The PDF.js Viewer WordPress plugin before 2.1.8 does not validate and escape some of its shortcode attributes before outputting them back in a page/post where the shortcode is embed, which could allow users with the contributor role and above to perform Stored Cross-Site Scripting attacks.
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Analysis
by VulDB Data Team • 03/25/2025
The vulnerability identified as CVE-2022-4670 affects the PDF.js Viewer WordPress plugin version 2.1.7 and earlier, representing a critical security flaw that enables stored cross-site scripting attacks through improper input validation and output escaping mechanisms. This issue specifically targets the plugin's shortcode attribute handling system where user-supplied parameters are not adequately sanitized before being rendered back to the browser, creating an avenue for malicious actors to inject persistent malicious scripts.
The technical flaw resides in the plugin's failure to implement proper input validation and output escaping for shortcode attributes, which directly correlates to CWE-79 - Improper Neutralization of Input During Web Page Generation. When administrators or users with contributor privileges and above embed PDF content using the plugin's shortcode functionality, the system processes attributes such as URL parameters, document identifiers, and configuration options without sufficient sanitization. This weakness allows attackers to craft malicious payloads that get stored within the WordPress database and subsequently executed whenever the affected page or post is rendered, making it a persistent threat rather than a one-time exploit.
The operational impact of this vulnerability extends beyond simple XSS attacks as it provides attackers with elevated privileges to manipulate content and potentially compromise user sessions. Contributors and above roles in WordPress typically have the ability to create and edit posts, which means an attacker could inject malicious scripts that execute in the context of other users' browsers. This could lead to session hijacking, credential theft, or further exploitation of the WordPress installation. The stored nature of the vulnerability means that once injected, the malicious code persists until manually removed, making it particularly dangerous in environments where multiple users interact with the same content.
From a threat modeling perspective, this vulnerability aligns with ATT&CK technique T1566.001 - Phishing: Spearphishing Attachment, as attackers could craft malicious PDF documents or HTML content that, when viewed through the vulnerable plugin, executes malicious scripts. The compromise of the PDF.js Viewer plugin creates a persistent backdoor for attackers who can leverage the contributor role privileges to inject scripts that can modify content, steal cookies, or redirect users to malicious sites. Security teams should prioritize immediate patching of this vulnerability, as it provides attackers with a reliable method to establish persistent presence within WordPress installations.
Mitigation strategies should include immediate upgrade to version 2.1.8 or later of the PDF.js Viewer plugin, which addresses the input validation and output escaping issues. Additionally, administrators should implement proper role-based access controls, monitor for suspicious shortcode usage, and consider implementing content security policies to limit script execution. Regular security audits of WordPress plugins and themes remain essential, as this vulnerability demonstrates how seemingly benign functionality can become a vector for sophisticated attacks. The incident underscores the importance of proper input validation and output escaping in web applications, particularly in content management systems where user-generated content processing occurs. Organizations should also consider implementing web application firewalls and regular security scanning to detect similar vulnerabilities in other components of their WordPress infrastructure.