CVE-2025-65403
📋 TL;DR
A buffer overflow vulnerability in LightFTP v2.0's g_cfg.MaxUsers component allows attackers to trigger a Denial of Service (DoS) by sending specially crafted input. This affects all systems running vulnerable versions of LightFTP server software. The vulnerability can be exploited remotely without authentication.
💻 Affected Systems
- LightFTP
📦 What is this software?
Lightftp by Hfiref0x
⚠️ Risk & Real-World Impact
Worst Case
Complete service disruption of the FTP server, potentially requiring manual restart or system reboot to restore functionality.
Likely Case
FTP service crash resulting in temporary unavailability until the service is restarted.
If Mitigated
Minimal impact with proper network segmentation and monitoring allowing quick detection and response.
🎯 Exploit Status
The vulnerability requires sending crafted input to the FTP server, which is straightforward for attackers with network access.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Not available
Vendor Advisory: https://github.com/hfiref0x/LightFTP
Restart Required: Yes
Instructions:
1. Monitor the LightFTP GitHub repository for security updates. 2. When a patched version is released, download and install it. 3. Restart the LightFTP service.
🔧 Temporary Workarounds
Network Access Restriction
allLimit FTP server access to trusted IP addresses only
# Use firewall rules to restrict access
# Example: iptables -A INPUT -p tcp --dport 21 -s trusted_ip -j ACCEPT
# Example: iptables -A INPUT -p tcp --dport 21 -j DROP
Service Monitoring and Auto-restart
allImplement monitoring to detect crashes and automatically restart the service
# Use systemd or supervisor to auto-restart
# Example systemd: Restart=always in service file
# Example cron: */5 * * * * systemctl is-active --quiet lightftp || systemctl start lightftp
🧯 If You Can't Patch
- Implement strict network segmentation to isolate FTP servers from untrusted networks
- Deploy intrusion detection systems (IDS) to monitor for exploitation attempts and anomalous FTP traffic
🔍 How to Verify
Check if Vulnerable:
Check LightFTP version: if running v2.0, the system is vulnerable. No specific exploit check available without testing.Check Version:
# Linux: lightftp --version or check process info
# Windows: Check program properties or installed programs listVerify Fix Applied:
Verify LightFTP version is updated to a patched release when available. Test FTP service functionality after update.📡 Detection & Monitoring
Log Indicators:
- Unexpected FTP service crashes
- Error messages related to buffer overflow or memory corruption
- Multiple failed connection attempts from single source
Network Indicators:
- Unusual FTP traffic patterns
- Multiple connection attempts with malformed data
- Traffic spikes followed by service unavailability
SIEM Query:
source="ftp.log" ("crash" OR "buffer overflow" OR "segmentation fault") OR (event="service_stop" AND service="lightftp")