CVE-2025-15549
📋 TL;DR
FluentCMS 2026 contains a stored cross-site scripting vulnerability where authenticated administrators can upload malicious SVG files containing JavaScript via the File Management module. When users access these uploaded SVG files, the embedded JavaScript executes in their browsers. This affects all FluentCMS 2026 installations with administrator accounts.
💻 Affected Systems
- FluentCMS
📦 What is this software?
Fluentcms by Fluentcms
⚠️ Risk & Real-World Impact
Worst Case
Attackers with administrator credentials could upload malicious SVG files that steal session cookies, redirect users to phishing sites, or perform actions on behalf of authenticated users, potentially leading to complete system compromise.
Likely Case
Attackers with compromised administrator accounts upload malicious SVG files that steal user session tokens or credentials when accessed, leading to account takeover and lateral movement within the application.
If Mitigated
With proper input validation and content security policies, malicious SVG uploads are blocked, limiting impact to potential file upload abuse without code execution.
🎯 Exploit Status
Exploitation requires administrator credentials but is straightforward once authenticated. Public proof-of-concept exists in GitHub issue.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Not available
Vendor Advisory: https://github.com/fluentcms/FluentCMS/issues/2404
Restart Required: No
Instructions:
No official patch available. Monitor GitHub repository for updates and apply when released.
🔧 Temporary Workarounds
Disable SVG uploads
allConfigure FluentCMS to block SVG file uploads in the File Management module
Modify file upload configuration to reject .svg extensions
Implement Content Security Policy
allAdd CSP headers to prevent inline script execution from uploaded files
Add 'Content-Security-Policy: script-src 'self'' header to web server configuration
🧯 If You Can't Patch
- Restrict administrator account access and implement multi-factor authentication
- Monitor file upload logs for SVG files and investigate any suspicious uploads
🔍 How to Verify
Check if Vulnerable:
Check if authenticated administrator can upload SVG files containing JavaScript via File Management module and if they execute when accessedCheck Version:
Check FluentCMS version in admin panel or configuration filesVerify Fix Applied:
Test SVG upload with embedded JavaScript - should be blocked or sanitized📡 Detection & Monitoring
Log Indicators:
- SVG file uploads by administrator accounts
- Large number of SVG file accesses
Network Indicators:
- HTTP requests to uploaded SVG files with suspicious parameters
SIEM Query:
source="fluentcms" AND (file_extension=".svg" OR file_type="image/svg+xml")