CVE-2025-5356: FreeFloat FTP Server Buffer Overflow Flaw

CVE-2025-5356 Overview

A critical buffer overflow vulnerability has been identified in FreeFloat FTP Server 1.0 affecting the BYE Command Handler component. This vulnerability allows remote attackers to exploit improper boundary checking when processing the BYE command, potentially leading to memory corruption and system compromise.

Critical Impact

Remote attackers can exploit this buffer overflow vulnerability over the network without authentication, potentially causing service disruption, memory corruption, and compromise of the affected FTP server.

Affected Products

• FreeFloat FTP Server 1.0

Discovery Timeline

• 2025-05-30 - CVE-2025-5356 published to NVD
• 2025-06-24 - Last updated in NVD database

Technical Details for CVE-2025-5356

Vulnerability Analysis

This vulnerability resides in the BYE Command Handler of FreeFloat FTP Server 1.0. The vulnerability is classified as CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer), indicating that the application fails to properly validate input length before copying data into a fixed-size buffer.

When an attacker sends a specially crafted BYE command with excessive data, the application does not perform adequate bounds checking, resulting in adjacent memory being overwritten. This buffer overflow condition can corrupt critical program data structures, overwrite return addresses on the stack, or modify control flow data.

The exploit has been publicly disclosed and is available for use, increasing the risk of exploitation in the wild. Organizations running FreeFloat FTP Server 1.0 should treat this vulnerability with urgency.

Root Cause

The root cause of CVE-2025-5356 is improper input validation in the BYE command processing routine. The BYE Command Handler fails to enforce proper boundary checks on user-supplied input before copying it into a fixed-size memory buffer. This lack of input length validation allows attackers to supply data exceeding the buffer's allocated size, triggering a classic buffer overflow condition.

Attack Vector

The attack vector is network-based, requiring no authentication or user interaction. An attacker can remotely connect to the vulnerable FTP server on its listening port and send a malformed BYE command containing oversized data. The exploitation flow involves:

1. Establishing a TCP connection to the FTP server
2. Sending a crafted BYE command with payload data exceeding expected buffer size
3. The server processes the command without proper bounds checking
4. Memory adjacent to the buffer is overwritten, potentially including return addresses or function pointers
5. Depending on the payload, this can result in denial of service or potentially arbitrary code execution

Technical details regarding the specific exploitation methodology can be found in the Fitoxs Exploit Report.

Detection Methods for CVE-2025-5356

Indicators of Compromise

• Unusual FTP traffic patterns with abnormally large BYE command payloads
• FTP server crashes or unexpected service restarts
• Memory access violations in FreeFloat FTP Server process logs
• Network connections to FTP service followed by immediate disconnection or service failure

Detection Strategies

• Deploy network intrusion detection signatures to identify oversized BYE commands in FTP traffic
• Monitor FTP server process for crashes, exceptions, or abnormal memory consumption
• Implement deep packet inspection for FTP command analysis on port 21
• Review application logs for malformed command errors or buffer-related exceptions

Monitoring Recommendations

• Enable verbose logging on FTP servers to capture command details
• Set up alerts for FTP service crashes or automatic restarts
• Monitor network traffic for unusual patterns to FTP services, particularly commands with excessive payload sizes
• Implement file integrity monitoring on FTP server binaries and configuration files

How to Mitigate CVE-2025-5356

Immediate Actions Required

• Discontinue use of FreeFloat FTP Server 1.0 if possible and migrate to a supported, actively maintained FTP server solution
• Implement network segmentation to restrict access to FTP services from untrusted networks
• Deploy network-level filtering to limit FTP access to authorized IP addresses only
• Consider placing the FTP server behind a web application firewall or network security appliance capable of protocol inspection

Patch Information

No vendor patch information is currently available for this vulnerability. FreeFloat FTP Server appears to be legacy software without active maintenance. Organizations are strongly advised to evaluate alternative FTP server solutions with active security support.

For additional vulnerability analysis, refer to the VulDB CVE Analysis #310650.

Workarounds

• Restrict network access to the FTP server using firewall rules to allow only trusted IP addresses
• Disable or remove the FTP service if not required for business operations
• Implement connection rate limiting to slow potential exploitation attempts
• Consider deploying an FTP proxy or gateway that can inspect and filter malformed commands before they reach the vulnerable server

# Firewall configuration to restrict FTP access (iptables example)
# Allow FTP only from trusted network segment
iptables -A INPUT -p tcp --dport 21 -s 10.0.0.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 21 -j DROP

# Enable logging for blocked FTP attempts
iptables -A INPUT -p tcp --dport 21 -j LOG --log-prefix "FTP_BLOCKED: "