CVE-2020-37067: Filetto FTP Server DoS Vulnerability

CVE-2020-37067 Overview

CVE-2020-37067 is a denial of service vulnerability affecting the Filetto 1.0 FTP server. The vulnerability exists in the FEAT command processing functionality, where sending an oversized FEAT command containing 11,008 bytes of repeated characters triggers a buffer overflow condition. This causes the FTP service to crash, resulting in service unavailability for legitimate users.

Critical Impact

Attackers can remotely crash the Filetto FTP server with a single malformed FEAT command, causing complete service disruption without requiring authentication credentials beyond basic FTP access.

Affected Products

• Filetto 1.0 FTP Server

Discovery Timeline

• 2026-02-03 - CVE CVE-2020-37067 published to NVD
• 2026-02-04 - Last updated in NVD database

Technical Details for CVE-2020-37067

Vulnerability Analysis

The Filetto 1.0 FTP server fails to properly validate the length of input received via the FEAT command before processing it. The FEAT command, which is part of the FTP protocol and used to request a list of extended features supported by the server, does not implement adequate boundary checking. When an attacker sends a FEAT command with an unusually large payload of approximately 11,008 bytes, the server attempts to process this oversized input, leading to a buffer overflow condition that terminates the FTP service.

This vulnerability is classified under CWE-770 (Allocation of Resources Without Limits or Throttling), indicating the root cause is improper resource allocation when handling the malformed command. The network-accessible nature of FTP services makes this vulnerability particularly concerning, as attackers can trigger the denial of service condition remotely with minimal prerequisites.

Root Cause

The vulnerability stems from insufficient input validation and improper memory allocation handling in the FEAT command parser. The Filetto FTP server does not enforce length restrictions on incoming FEAT commands, allowing attackers to send payloads far exceeding expected parameters. When the server receives approximately 11,008 bytes of data in a single FEAT command, the buffer allocated for command processing is overwhelmed, causing memory corruption and subsequent service termination.

Attack Vector

The attack is network-based and can be executed by any authenticated FTP user. An attacker establishes a connection to the vulnerable Filetto FTP server, authenticates with valid credentials (which may be default or easily obtainable in many FTP deployments), and then sends a malformed FEAT command containing thousands of repeated characters. The server's failure to sanitize this input results in immediate service crash.

The attack requires low complexity to execute and does not require any user interaction beyond the attacker's own actions. While the attack does not compromise confidentiality or integrity, it completely disrupts service availability. A public exploit for this vulnerability is documented on Exploit-DB #48503.

Detection Methods for CVE-2020-37067

Indicators of Compromise

• Abnormally large FTP command packets (>10KB) targeting the FEAT command
• FTP service crashes or unexpected restarts without administrative action
• Network traffic containing repetitive character patterns in FTP command streams
• Log entries showing malformed or oversized FEAT command attempts

Detection Strategies

• Deploy network intrusion detection rules to alert on FTP FEAT commands exceeding normal size thresholds (typically under 1KB)
• Monitor FTP server process stability and configure alerts for unexpected service terminations
• Implement deep packet inspection for FTP traffic to identify oversized command payloads
• Review FTP server logs for repeated connection attempts followed by immediate service failures

Monitoring Recommendations

• Enable verbose logging on FTP servers to capture command-level detail
• Configure process monitoring to alert when the Filetto FTP service unexpectedly terminates
• Establish baseline metrics for FTP command sizes and alert on anomalies
• Deploy network flow analysis to detect unusual traffic patterns targeting FTP services

How to Mitigate CVE-2020-37067

Immediate Actions Required

• Consider replacing Filetto 1.0 with an actively maintained FTP server solution
• Restrict network access to the FTP server using firewall rules to limit exposure
• Implement network-level rate limiting to slow potential denial of service attempts
• Deploy a Web Application Firewall (WAF) or network security appliance capable of inspecting FTP traffic

Patch Information

No official patch information is available from the vendor. The SourceForge Project Page and Utillyty Homepage may contain updated versions or announcements. Organizations should consult the VulnCheck Denial of Service Advisory for the latest remediation guidance.

Workarounds

• Migrate to an alternative FTP server solution with active security support
• Place the FTP server behind a reverse proxy or load balancer that can filter oversized commands
• Implement strict IP whitelisting to limit access to trusted users only
• Use network segmentation to isolate the FTP server from critical infrastructure

# Example firewall rule to limit FTP access to trusted networks
iptables -A INPUT -p tcp --dport 21 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 21 -j DROP