Stored XSS in Nexter Blocks WordPress Plugin

Executive Summary

The Nexter Blocks WordPress plugin before version 5.0.2 has a vulnerability where it does not properly sanitize uploaded SVG files. This allows users with upload permissions, such as Authors, to upload SVG files containing malicious JavaScript. When these files are accessed, the embedded script executes, resulting in a Stored Cross-Site Scripting (XSS) attack.

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Detection Guidance

Check for unauthorized SVG file uploads in WordPress directories, particularly in the uploads folder. Look for files with .svg extension that contain JavaScript code or unusual content. Review user roles with upload permissions like Authors.

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Impact Analysis

This vulnerability can allow attackers to inject malicious scripts into your WordPress site. If exploited, it could lead to unauthorized actions on behalf of users, theft of sensitive data, or defacement of your website. Users with Author privileges or higher could upload malicious files.

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Compliance Impact

This vulnerability could lead to data breaches, which may violate GDPR or HIPAA requirements for protecting user data. A successful XSS attack could expose personal or health information, resulting in non-compliance with these regulations and potential legal consequences.

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Mitigation Strategies

Update the Nexter Blocks plugin to version 5.0.2 or later immediately. Remove any suspicious SVG files from the uploads directory. Restrict file upload permissions to only trusted users and disable SVG uploads if not required.

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