CVE-2019-25611: MiniFtp Buffer Overflow Vulnerability

CVE-2019-25611 Overview

MiniFtp contains a buffer overflow vulnerability in the parseconf_load_setting function that allows local attackers to execute arbitrary code by supplying oversized configuration values. Attackers can craft a miniftpd.conf file with values exceeding 128 bytes to overflow stack buffers and overwrite the return address, enabling code execution with root privileges.

Critical Impact

Local attackers can achieve arbitrary code execution with root privileges by exploiting the stack buffer overflow through malicious configuration file manipulation.

Affected Products

• MiniFtp (all versions with vulnerable parseconf_load_setting function)

Discovery Timeline

• 2026-03-22 - CVE CVE-2019-25611 published to NVD
• 2026-03-23 - Last updated in NVD database

Technical Details for CVE-2019-25611

Vulnerability Analysis

This vulnerability is classified as CWE-787 (Out-of-bounds Write), a critical memory corruption issue affecting the MiniFtp FTP server application. The flaw exists in the parseconf_load_setting function, which is responsible for parsing and loading configuration values from the miniftpd.conf configuration file.

The vulnerable function allocates a fixed-size stack buffer of 128 bytes to store configuration values read from the file. However, the function fails to properly validate the length of input values before copying them into this buffer. When a configuration value exceeds 128 bytes, the excess data overwrites adjacent stack memory, including the saved return address.

This stack-based buffer overflow enables attackers with local access to craft a malicious configuration file that triggers arbitrary code execution when the FTP daemon processes the configuration. Since FTP servers commonly run with elevated privileges to bind to privileged ports and manage user sessions, successful exploitation typically results in code execution with root privileges.

Root Cause

The root cause is insufficient bounds checking in the parseconf_load_setting function when processing configuration file values. The function uses a fixed-size 128-byte stack buffer without validating that input data fits within this allocation before performing the copy operation. This classic stack buffer overflow pattern allows attackers to corrupt stack memory and hijack program control flow.

Attack Vector

The attack requires local access to the system where MiniFtp is installed. An attacker must be able to modify or replace the miniftpd.conf configuration file with a malicious version containing oversized values. When the MiniFtp daemon starts or reloads its configuration, it processes the malicious file, triggering the buffer overflow.

The attacker crafts configuration values exceeding 128 bytes to overflow the stack buffer. By carefully controlling the overflow data, the attacker can overwrite the function's return address with a pointer to attacker-controlled code or a ROP gadget chain. Upon function return, execution transfers to the attacker's payload, achieving arbitrary code execution with the daemon's privileges.

Technical details and a proof-of-concept exploit are available through Exploit-DB #46807 and the VulnCheck Advisory.

Detection Methods for CVE-2019-25611

Indicators of Compromise

• Presence of unusually large miniftpd.conf configuration files or configuration values exceeding 128 bytes
• MiniFtp process crashes or unexpected termination followed by suspicious process spawning
• Evidence of configuration file tampering with timestamps inconsistent with normal administrative changes
• Abnormal system calls or network connections originating from the MiniFtp process

Detection Strategies

• Monitor file integrity of /etc/miniftpd.conf and any other MiniFtp configuration files for unauthorized modifications
• Implement system call auditing to detect exploitation attempts and post-compromise activity from the FTP service
• Deploy endpoint detection solutions capable of identifying buffer overflow exploitation techniques and shellcode execution
• Configure crash dump analysis to capture and analyze MiniFtp crashes that may indicate exploitation attempts

Monitoring Recommendations

• Enable detailed logging for the MiniFtp service and monitor for unusual restart patterns
• Implement file integrity monitoring (FIM) on configuration directories with alerting on unexpected changes
• Monitor process execution chains to detect suspicious child processes spawned by the MiniFtp daemon
• Review system authentication logs for any privilege escalation attempts following FTP service anomalies

How to Mitigate CVE-2019-25611

Immediate Actions Required

• Restrict file system permissions on miniftpd.conf to prevent unauthorized modification (root-only write access)
• Consider replacing MiniFtp with a more actively maintained and security-hardened FTP server solution
• Implement strict access controls limiting which users can modify FTP server configuration files
• Run MiniFtp in a sandboxed or containerized environment to limit the impact of successful exploitation

Patch Information

Review the MiniFtp GitHub Repository for any available patches or updated versions addressing this vulnerability. The VulnCheck Advisory provides additional guidance on remediation options.

Workarounds

• Restrict write permissions on the configuration file to root only using chmod 600 and chown root:root
• Run MiniFtp in a chroot jail or container to limit the blast radius of successful exploitation
• Implement mandatory access control (MAC) policies using SELinux or AppArmor to confine the FTP daemon
• Consider network segmentation to isolate systems running MiniFtp from critical infrastructure

# Secure MiniFtp configuration file permissions
chmod 600 /etc/miniftpd.conf
chown root:root /etc/miniftpd.conf

# Verify configuration file size is reasonable (should be small)
wc -c /etc/miniftpd.conf

# Check for any configuration values exceeding safe length
awk -F'=' '{if(length($2) > 100) print "WARNING: Long value in line " NR ": " $1}' /etc/miniftpd.conf