CVE-2019-25614: Freefloat FTP Buffer Overflow Vulnerability

CVE-2019-25614 Overview

Free Float FTP Server 1.0 contains a critical buffer overflow vulnerability in the STOR command handler that allows remote attackers to execute arbitrary code. By sending a crafted STOR request with an oversized payload, attackers can overwrite memory and gain control of program execution. The vulnerability is particularly dangerous because it can be exploited with anonymous credentials, requiring no prior authentication to the FTP server.

Critical Impact

Remote attackers can achieve arbitrary code execution on vulnerable FTP servers by sending a malicious STOR command containing 247 bytes of padding followed by a return address and shellcode.

Affected Products

• Free Float FTP Server 1.0
• freefloat:freefloat_ftp_server version 1.0

Discovery Timeline

• 2026-03-22 - CVE CVE-2019-25614 published to NVD
• 2026-03-23 - Last updated in NVD database

Technical Details for CVE-2019-25614

Vulnerability Analysis

This buffer overflow vulnerability (CWE-787: Out-of-bounds Write) exists in the STOR command handler of Free Float FTP Server. The server fails to properly validate the length of user-supplied input when processing STOR commands, allowing attackers to overflow a fixed-size buffer on the stack. When exploited, the attacker can overwrite the return address on the stack and redirect execution flow to attacker-controlled shellcode.

The vulnerability is classified as network-exploitable with low attack complexity, meaning remote attackers can reach the vulnerable component over the network without requiring any user interaction or special privileges. The anonymous authentication support in the FTP server significantly lowers the barrier to exploitation.

Root Cause

The root cause is improper input validation in the STOR command processing routine. The server allocates a fixed-size buffer for handling incoming STOR requests but fails to enforce boundary checks when copying user-supplied data into this buffer. This classic stack-based buffer overflow pattern allows an attacker to write beyond the allocated buffer boundaries, corrupting adjacent stack memory including saved return addresses.

Attack Vector

The attack is executed remotely over the network via the FTP protocol. An attacker connects to the vulnerable FTP server, authenticates using anonymous credentials (typically anonymous with any password), and then sends a specially crafted STOR command. The malicious payload consists of:

1. Padding: 247 bytes of filler data to reach the buffer boundary
2. Return Address: A carefully chosen memory address that redirects execution
3. Shellcode: Executable code that performs the attacker's desired actions (e.g., spawning a reverse shell)

The vulnerability can be exploited using standard FTP client tools or custom scripts. Additional technical details and proof-of-concept information can be found in Exploit-DB #46763 and the VulnCheck Advisory on FreeFloat FTP.

Detection Methods for CVE-2019-25614

Indicators of Compromise

• FTP server crashes or unexpected service restarts indicating potential exploitation attempts
• Unusually large STOR command requests in FTP server logs (particularly those exceeding 247 bytes)
• Anonymous FTP login attempts followed by immediate STOR commands with no file upload completion
• Suspicious outbound network connections from the FTP server process (indicating potential reverse shell connections)

Detection Strategies

• Deploy network intrusion detection rules to identify malformed or oversized STOR commands targeting FTP services
• Monitor FTP server logs for authentication attempts using anonymous credentials followed by abnormal command patterns
• Implement endpoint detection and response (EDR) solutions to detect shellcode execution or suspicious child processes spawned by the FTP server

Monitoring Recommendations

• Enable detailed FTP server logging and centralize logs for analysis
• Configure alerts for FTP service crashes or unexpected process terminations
• Monitor network traffic for patterns consistent with buffer overflow exploitation payloads
• Use SentinelOne's behavioral AI to detect post-exploitation activities such as reverse shell connections or lateral movement

How to Mitigate CVE-2019-25614

Immediate Actions Required

• Discontinue use of Free Float FTP Server 1.0 and migrate to a maintained, secure FTP server solution
• Block external access to the FTP service at the network perimeter if the service must remain operational
• Disable anonymous FTP authentication to reduce the attack surface
• Deploy network segmentation to isolate FTP servers from critical infrastructure

Patch Information

No official patch is available from the vendor for this vulnerability. The Free Float FTP Server software appears to be unmaintained. Organizations are strongly advised to migrate to an actively supported FTP server solution that receives regular security updates. For reference, the original software is available at FreeFloat FTP Server Download, though its use is not recommended.

Workarounds

• Replace Free Float FTP Server with a secure, actively maintained alternative such as FileZilla Server, vsftpd, or ProFTPD
• Implement network-level access controls to restrict FTP access to trusted IP addresses only
• Deploy a web application firewall (WAF) or intrusion prevention system (IPS) with rules to block oversized FTP commands
• If migration is not immediately possible, run the FTP server in a sandboxed environment with limited system privileges