CVE-2025-15678: Nexter Blocks WordPress XSS Vulnerability

CVE-2025-15678 Overview

CVE-2025-15678 is a Stored Cross-Site Scripting (XSS) vulnerability in the Nexter Blocks WordPress plugin prior to version 5.0.2. The plugin permits Scalable Vector Graphics (SVG) uploads for any user with file upload permissions, including the default Author role. It fails to sanitize the contents of uploaded SVG files, allowing embedded JavaScript to persist. When another user, including administrators, accesses the file, the malicious script executes in their browser session.

Critical Impact
Authenticated users with Author-level access can upload weaponized SVG files that trigger Stored XSS against any visitor or administrator who views the file.

Affected Products

Nexter Blocks WordPress plugin versions before 5.0.2
WordPress installations permitting Author-level uploads
Sites relying on default WordPress role capabilities with Nexter Blocks installed

Discovery Timeline

2026-08-06 - CVE-2025-15678 published to NVD
2026-08-06 - Last updated in NVD database

Technical Details for CVE-2025-15678

Vulnerability Analysis

The Nexter Blocks plugin extends WordPress upload handling to accept SVG files. WordPress natively rejects SVG uploads because the format supports embedded scripting through <script> tags and event handler attributes such as onload. The plugin bypasses this restriction without applying sanitization to the file contents. Any authenticated user granted the upload_files capability, which includes the default Author role, can upload arbitrary SVG payloads. The stored file is served with an XML content type, and browsers execute embedded scripts when the file is loaded directly or referenced from another page.

Root Cause

The vulnerability stems from missing input sanitization on file uploads [CWE-79]. The plugin whitelists the SVG MIME type without parsing the XML body to strip <script> elements, javascript: URIs, or event handler attributes. It also does not restrict SVG uploads to trusted roles such as Editor or Administrator.

Attack Vector

An attacker with Author credentials crafts an SVG file containing JavaScript inside a <script> tag or an onload handler on the root <svg> element. The attacker uploads the file through the WordPress media library. The plugin stores the file unmodified in the uploads directory. When an administrator previews the media item or a visitor opens the direct URL, the browser parses the SVG as XML and executes the embedded script under the site's origin. The script can steal session cookies, perform actions on behalf of the victim, or plant additional persistence.

See the WPScan Vulnerability Report for technical details.

Detection Methods for CVE-2025-15678

Indicators of Compromise

SVG files in the wp-content/uploads/ directory containing <script> tags, javascript: URIs, or on* event handler attributes
Media library entries uploaded by low-privileged Author accounts with .svg extensions
Outbound requests from administrator browser sessions to unknown domains following SVG file access
Unexpected creation of administrator accounts or plugin installations shortly after SVG media views

Detection Strategies

Scan the uploads directory for SVG files and inspect their XML content for scripting constructs
Audit the WordPress wp_posts table for attachment post types with post_mime_type of image/svg+xml
Correlate SVG upload events with the uploading user's role and recent privilege changes
Review web server access logs for direct requests to .svg files from administrative IPs

Monitoring Recommendations

Alert on any SVG upload originating from non-Administrator accounts
Log all file upload events with user, role, filename, and content hash for retrospective review
Monitor administrator session activity for anomalies immediately following media library interactions
Track installations and updates of the Nexter Blocks plugin across managed WordPress fleets

How to Mitigate CVE-2025-15678

Immediate Actions Required

Update the Nexter Blocks plugin to version 5.0.2 or later on all WordPress instances
Audit existing SVG files in the uploads directory and remove any containing script content or event handlers
Review user roles and revoke Author privileges from accounts that do not require file uploads
Rotate administrator credentials and invalidate active sessions if malicious SVG uploads are found

Patch Information

Upgrade Nexter Blocks to version 5.0.2, which addresses the missing SVG sanitization. Refer to the WPScan Vulnerability Report for the fixed version reference.

Workarounds

Disable the Nexter Blocks plugin until it can be upgraded to a patched release
Restrict the upload_files capability using a role management plugin so only trusted roles can upload media
Add a server-level rule to reject .svg uploads or serve them with the Content-Disposition: attachment header to prevent inline rendering
Deploy a Web Application Firewall (WAF) rule that inspects SVG uploads for <script> tags and on* event handlers

bash

# Example Apache configuration to force SVG files to download rather than render
<FilesMatch "\.svg$">
    Header set Content-Disposition "attachment"
    Header set Content-Security-Policy "default-src 'none'; script-src 'none'"
</FilesMatch>