CVE-2023-51803
📋 TL;DR
This vulnerability in Heimdall allows attackers to upload malicious icons containing PHP code, potentially leading to remote code execution. It affects all Heimdall instances before version 2.5.7 that allow icon uploads. The high CVSS score reflects the potential for complete system compromise.
💻 Affected Systems
- LinuxServer.io Heimdall
⚠️ Manual Verification Required
This CVE does not have specific version information in our database, so automatic vulnerability detection cannot determine if your system is affected.
Why? The CVE database entry doesn't specify which versions are vulnerable (no version ranges provided by the vendor/NVD).
🔒 Custom verification scripts are available for registered users. Sign up free to download automated test scripts.
- Review the CVE details at NVD
- Check vendor security advisories for your specific version
- Test if the vulnerability is exploitable in your environment
- Consider updating to the latest version as a precaution
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete system takeover, data exfiltration, lateral movement, and persistent backdoor installation.
Likely Case
Webshell deployment allowing file system access, credential theft, and further exploitation of the hosting environment.
If Mitigated
Limited impact with proper file upload restrictions and web application firewalls blocking malicious payloads.
🎯 Exploit Status
Exploitation requires authenticated access to upload icons. The vulnerability is straightforward to exploit once authenticated.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2.5.7
Vendor Advisory: https://github.com/linuxserver/Heimdall/releases/tag/v2.5.7
Restart Required: Yes
Instructions:
1. Backup your Heimdall configuration and database. 2. Update to version 2.5.7 via your package manager or Docker. 3. Restart the Heimdall service. 4. Verify the update completed successfully.
🔧 Temporary Workarounds
Disable Icon Uploads
allTemporarily disable the ability to upload custom icons in Heimdall configuration
Edit Heimdall configuration to remove icon upload functionality
Web Application Firewall Rules
allImplement WAF rules to block file uploads containing PHP code patterns
Add WAF rule: block requests with file uploads containing '<?php' or similar patterns
🧯 If You Can't Patch
- Restrict access to Heimdall to trusted users only using network segmentation
- Implement strict file upload validation at the web server level (e.g., nginx/apache rules)
🔍 How to Verify
Check if Vulnerable:
Check Heimdall version in web interface or via command: docker exec heimdall cat /app/www/version.txtCheck Version:
docker exec heimdall cat /app/www/version.txt || check web interface settingsVerify Fix Applied:
Confirm version is 2.5.7 or higher and test that PHP files cannot be uploaded as icons📡 Detection & Monitoring
Log Indicators:
- File upload attempts with .php extensions
- Web server logs showing execution of uploaded files
- Unusual file creation in upload directories
Network Indicators:
- HTTP POST requests to icon upload endpoints with suspicious content
- Outbound connections from Heimdall server to unknown IPs
SIEM Query:
source="heimdall" AND (url_path="/upload" OR file_extension=".php")🔗 References
- https://github.com/linuxserver/Heimdall/pull/1167
- https://github.com/linuxserver/Heimdall/pull/1173
- https://github.com/linuxserver/Heimdall/releases/tag/v2.5.7
- https://github.com/linuxserver/Heimdall/pull/1167
- https://github.com/linuxserver/Heimdall/pull/1173
- https://github.com/linuxserver/Heimdall/releases/tag/v2.5.7
