CVE-2025-3902 in Block Class
Summary
by MITRE • 04/23/2025
Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') vulnerability in Drupal Block Class allows Cross-Site Scripting (XSS).This issue affects Block Class: from 4.0.0 before 4.0.1.
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Analysis
by VulDB Data Team • 06/17/2025
The vulnerability identified as CVE-2025-3902 represents a critical cross-site scripting flaw within the Drupal Block Class module, specifically impacting versions 4.0.0 through 4.0.0. This weakness falls under the well-established CWE-79 category for improper neutralization of input during web page generation, making it a classic XSS vulnerability that can severely compromise user sessions and data integrity. The flaw occurs when the Block Class module fails to properly sanitize user-supplied input before incorporating it into dynamically generated web pages, creating an avenue for malicious actors to inject arbitrary JavaScript code into the application's output.
The technical implementation of this vulnerability stems from insufficient input validation and output encoding within the Block Class module's rendering process. When administrators or users create or modify block content through the Drupal administrative interface, the module does not adequately escape or filter special characters that could be interpreted as HTML or JavaScript markup. This failure allows attackers to craft malicious payloads that, when processed by the vulnerable module, execute in the context of other users' browsers. The vulnerability is particularly dangerous because it operates at the web application layer, where user interactions directly influence page generation, making it difficult to distinguish between legitimate and malicious content without proper sanitization measures.
The operational impact of this vulnerability extends beyond simple script execution, potentially enabling session hijacking, credential theft, and data manipulation across the affected Drupal installation. Attackers can exploit this weakness to inject malicious scripts that capture user credentials, redirect victims to fraudulent sites, or modify content displayed to other users. The vulnerability affects the core functionality of the Block Class module, which is commonly used for creating dynamic content blocks, making it a widespread potential attack vector across numerous Drupal deployments. Given that Drupal is a widely adopted content management system, this vulnerability could impact thousands of websites simultaneously, particularly those running vulnerable versions of the Block Class module.
Mitigation strategies for CVE-2025-3902 should prioritize immediate version updates to 4.0.1 or later, as this release contains the necessary patches to address the input sanitization deficiencies. Organizations should implement comprehensive input validation at multiple layers of their application architecture, including both client-side and server-side filtering mechanisms. The implementation of Content Security Policy headers can provide additional defense-in-depth measures, while regular security audits and penetration testing should be conducted to identify similar vulnerabilities in other modules or custom code. This vulnerability aligns with ATT&CK technique T1566.001 for initial access through web application attacks, making it a critical target for defensive security operations. Security teams should also consider implementing web application firewalls and monitoring for suspicious input patterns that might indicate exploitation attempts, while maintaining detailed logging of user interactions with the Block Class module to facilitate incident response activities.