CVE-2023-31541
📋 TL;DR
CVE-2023-31541 is an unrestricted file upload vulnerability in the CKEditor v1.2.3 plugin for Redmine that allows attackers to upload arbitrary files to the server. This affects Redmine installations using the vulnerable CKEditor plugin version. Attackers can potentially upload malicious files like web shells to gain unauthorized access.
💻 Affected Systems
- Redmine CKEditor Plugin
📦 What is this software?
Ckeditor by Ckeditor
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete system compromise, data theft, and lateral movement within the network.
Likely Case
Web shell upload allowing persistent backdoor access, file system manipulation, and potential privilege escalation.
If Mitigated
File uploads blocked or sanitized, limiting impact to denial of service if upload attempts overwhelm storage.
🎯 Exploit Status
Exploitation requires access to the 'Browse and upload images' feature, which typically requires authentication. Public proof-of-concept demonstrates file upload bypass.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Version 1.2.4 or later
Vendor Advisory: http://redmineckeditor.com
Restart Required: Yes
Instructions:
1. Backup current Redmine installation. 2. Update CKEditor plugin to version 1.2.4 or later via Redmine plugin management. 3. Restart Redmine application server. 4. Verify plugin version in Redmine admin interface.
🔧 Temporary Workarounds
Disable CKEditor plugin
allTemporarily disable the vulnerable CKEditor plugin until patching is possible
Navigate to Redmine Admin > Plugins > Disable CKEditor plugin
Web server file type restrictions
linuxConfigure web server to block upload of executable file types
For Apache: Add 'Deny from all' to .htaccess in upload directory for dangerous extensions
For Nginx: Add location block denying uploads of .php, .jsp, .asp files
🧯 If You Can't Patch
- Implement strict file upload validation at application level (allow only image MIME types)
- Configure WAF rules to block malicious file upload patterns and suspicious POST requests
🔍 How to Verify
Check if Vulnerable:
Check Redmine admin panel > Plugins > CKEditor version. If version is 1.2.3, system is vulnerable.Check Version:
Check Redmine database: SELECT * FROM plugins WHERE name LIKE '%ckeditor%';Verify Fix Applied:
Verify CKEditor plugin version is 1.2.4 or later in Redmine admin interface. Test file upload functionality with non-image files - they should be rejected.📡 Detection & Monitoring
Log Indicators:
- Multiple failed file upload attempts
- Uploads of non-image file types to CKEditor endpoint
- Large POST requests to /ckeditor/upload endpoints
Network Indicators:
- Unusual file upload patterns to Redmine server
- POST requests with executable file extensions
SIEM Query:
source="redmine.log" AND ("upload" OR "ckeditor") AND ("php" OR "jsp" OR "asp" OR "exe")