CVE-2020-26804
📋 TL;DR
This vulnerability allows authenticated attackers to upload malicious files through Sentrifugo's announcement attachment feature, potentially leading to remote code execution and server compromise. It affects Sentrifugo 3.2 installations where users have announcement posting privileges. The unrestricted file upload bypasses security controls that should validate file types.
💻 Affected Systems
- Sentrifugo
📦 What is this software?
Sentrifugo by Sapplica
⚠️ Risk & Real-World Impact
Worst Case
Complete server takeover with attacker gaining shell access, installing backdoors, stealing sensitive data, and pivoting to other systems in the network.
Likely Case
Webshell deployment leading to data exfiltration, privilege escalation, and persistence on the compromised server.
If Mitigated
File upload attempts are blocked or quarantined, preventing malicious file execution while maintaining legitimate functionality.
🎯 Exploit Status
Exploitation requires authenticated access but is straightforward once credentials are obtained. Public blog posts demonstrate RCE techniques.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 3.3 or later
Vendor Advisory: https://github.com/sapplica/sentrifugo/releases
Restart Required: No
Instructions:
1. Backup your Sentrifugo installation and database. 2. Download Sentrifugo 3.3 or later from the official repository. 3. Replace the vulnerable files with patched versions. 4. Verify the upload functionality now validates file types properly.
🔧 Temporary Workarounds
Web Server File Extension Blocking
allConfigure web server to block execution of uploaded files with dangerous extensions
# Apache: Add to .htaccess
<FilesMatch "\.(php|phtml|php3|php4|php5|pl|py|jsp|asp|sh|cgi)$">
Order allow,deny
Deny from all
</FilesMatch>
# Nginx: Add to server block
location ~* \.(php|phtml|php3|php4|php5|pl|py|jsp|asp|sh|cgi)$ {
deny all;
}
Disable Announcement Attachments
allTemporarily disable file upload functionality in announcements module
# Modify Sentrifugo code to remove file upload capability
# Locate announcement upload handler and comment out or remove upload logic
🧯 If You Can't Patch
- Implement strict file type validation at the application level before accepting uploads
- Store uploaded files outside web root with randomized names and serve through secure download handlers
🔍 How to Verify
Check if Vulnerable:
Attempt to upload a file with PHP extension through the announcements attachment feature. If accepted without validation, the system is vulnerable.Check Version:
Check Sentrifugo version in admin panel or examine version.php file in installation directoryVerify Fix Applied:
Test file upload with various malicious extensions (php, jsp, asp, etc.) - all should be rejected. Verify only allowed file types (pdf, doc, images) are accepted.📡 Detection & Monitoring
Log Indicators:
- Unusual file uploads with executable extensions
- Multiple failed upload attempts with suspicious filenames
- Web server logs showing execution of uploaded files
Network Indicators:
- HTTP POST requests to announcement upload endpoint with unusual file types
- Outbound connections from web server to unknown IPs following uploads
SIEM Query:
source="web_server" AND (uri="*announcement*upload*" OR uri="*attachment*upload*") AND (file_extension="php" OR file_extension="jsp" OR file_extension="asp")