CVE-2020-26286
📋 TL;DR
CVE-2020-26286 is an unrestricted file upload vulnerability in HedgeDoc that allows unauthenticated attackers to upload arbitrary files including HTML, JavaScript, and PHP files to the upload storage backend. This affects all HedgeDoc instances before version 1.7.1. Attackers could upload malicious files that might be executed or served to users.
💻 Affected Systems
- HedgeDoc
📦 What is this software?
Hedgedoc by Hedgedoc
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution via uploaded PHP files leading to complete system compromise, data theft, or ransomware deployment.
Likely Case
Cross-site scripting attacks via uploaded HTML/JS files, session hijacking, or serving malicious content to users.
If Mitigated
Limited impact with proper file type validation and storage isolation, though uploaded malicious files could still be served.
🎯 Exploit Status
Exploitation requires only HTTP POST requests to the vulnerable endpoint with malicious files.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 1.7.1
Vendor Advisory: https://github.com/hedgedoc/hedgedoc/security/advisories/GHSA-wcr3-xhv7-8gxc
Restart Required: Yes
Instructions:
1. Backup your HedgeDoc instance and database. 2. Update to HedgeDoc 1.7.1 or later using your package manager or by downloading from GitHub releases. 3. Restart the HedgeDoc service. 4. Verify the update was successful by checking the version.
🔧 Temporary Workarounds
Block upload endpoint via reverse proxy
allBlock access to the vulnerable /uploadimage endpoint using reverse proxy rules.
# For nginx: location /uploadimage { deny all; }
# For Apache: <Location /uploadimage> Require all denied </Location>
Restrict MIME types and file names
allConfigure web server to only serve specific file types from upload storage.
# Example nginx config to block PHP files: location ~ \.php$ { deny all; }
🧯 If You Can't Patch
- Disable file upload functionality entirely in HedgeDoc configuration
- Implement strict file type validation at the reverse proxy/load balancer level
🔍 How to Verify
Check if Vulnerable:
Check if HedgeDoc version is below 1.7.1. Attempt to upload a file with disallowed extension to /uploadimage endpoint.Check Version:
Check HedgeDoc web interface footer or run: grep version /path/to/hedgedoc/package.jsonVerify Fix Applied:
Verify HedgeDoc version is 1.7.1 or higher. Test that file uploads with malicious extensions are rejected.📡 Detection & Monitoring
Log Indicators:
- Multiple POST requests to /uploadimage with unusual file extensions
- Uploads of files with .php, .html, .js extensions from unauthenticated users
Network Indicators:
- Unusual file upload traffic patterns
- POST requests to /uploadimage with malicious payloads
SIEM Query:
source="hedgedoc.log" AND (uri_path="/uploadimage" AND (file_extension="php" OR file_extension="html" OR file_extension="js"))🔗 References
- https://github.com/hedgedoc/hedgedoc/commit/e9306991cdb5ff2752c1eeba3fedba42aec3c2d8
- https://github.com/hedgedoc/hedgedoc/releases/tag/1.7.1
- https://github.com/hedgedoc/hedgedoc/security/advisories/GHSA-wcr3-xhv7-8gxc
- https://github.com/hedgedoc/hedgedoc/commit/e9306991cdb5ff2752c1eeba3fedba42aec3c2d8
- https://github.com/hedgedoc/hedgedoc/releases/tag/1.7.1
- https://github.com/hedgedoc/hedgedoc/security/advisories/GHSA-wcr3-xhv7-8gxc
