CVE-2020-20276
📋 TL;DR
An unauthenticated stack-based buffer overflow vulnerability in uftpd FTP server allows remote attackers to crash the service and potentially execute arbitrary code. This affects all systems running uftpd version 2.10 or earlier with FTP service enabled. Attackers can exploit this without any authentication.
💻 Affected Systems
- uftpd FTP server
📦 What is this software?
Uftpd by Troglobit
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution with full system compromise, allowing attacker to install malware, exfiltrate data, or pivot to other systems.
Likely Case
Service crash leading to denial of service, with potential for remote code execution in favorable conditions.
If Mitigated
Denial of service only if exploit fails or protections like ASLR/PIE are effective.
🎯 Exploit Status
Public proof-of-concept demonstrates crash, and buffer overflow characteristics suggest RCE is achievable. No authentication required.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2.11 and later
Vendor Advisory: https://github.com/troglobit/uftpd/commit/0fb2c031ce0ace07cc19cd2cb2143c4b5a63c9dd
Restart Required: Yes
Instructions:
1. Update uftpd to version 2.11 or later using your package manager or from source. 2. Restart the uftpd service. 3. Verify the service is running the patched version.
🔧 Temporary Workarounds
Disable FTP service
linuxCompletely disable uftpd FTP service if not required.
sudo systemctl stop uftpd
sudo systemctl disable uftpd
Network segmentation
linuxRestrict network access to FTP service using firewall rules.
sudo iptables -A INPUT -p tcp --dport 21 -j DROP
🧯 If You Can't Patch
- Implement strict network access controls to limit FTP service to trusted IPs only
- Monitor for exploitation attempts and have incident response procedures ready
🔍 How to Verify
Check if Vulnerable:
Check uftpd version: 'uftpd -v' or 'rpm -q uftpd' or 'dpkg -l uftpd'. If version is 2.10 or earlier, system is vulnerable.Check Version:
uftpd -v 2>&1 | head -1Verify Fix Applied:
After update, verify version is 2.11 or later using same commands and test FTP connectivity.📡 Detection & Monitoring
Log Indicators:
- Multiple failed FTP connections
- Unusual PORT command patterns
- uftpd crash logs
Network Indicators:
- Malformed FTP PORT commands with excessive data
- Traffic to FTP port 21 from unexpected sources
SIEM Query:
source="uftpd.log" AND "PORT" AND (data_length>normal OR crash)