Source: cve@mitre.org
FTP installation script anon.ftp in AIX insecurely configures anonymous FTP, which allows remote attackers to execute arbitrary commands.
Remote code execution is possible on vulnerable AIX systems due to an insecurely configured anonymous FTP service. Attackers can leverage this misconfiguration to upload and execute malicious commands, potentially leading to complete system compromise and data exfiltration.
Step 1: Connection Establishment: The attacker connects to the vulnerable AIX system's FTP service anonymously using the username 'anonymous' or 'ftp'.
Step 2: Payload Upload: The attacker uploads a malicious payload, such as a shell script or a compiled binary, to a writable directory accessible to the anonymous FTP user. This directory is likely the default upload directory configured by the anon.ftp script.
Step 3: Command Execution: The attacker triggers the execution of the uploaded payload. This could be achieved by exploiting a command injection vulnerability within the FTP service itself, or by simply executing the uploaded script through a command like !sh <uploaded_script> if the FTP service allows it.
Step 4: System Compromise: The malicious payload executes with the privileges of the FTP service (or potentially higher, depending on the script's configuration), allowing the attacker to gain control of the system. This could involve creating backdoors, stealing sensitive data, or further escalating privileges.
The vulnerability stems from the anon.ftp installation script's failure to properly secure the anonymous FTP configuration. Specifically, the script likely grants excessive permissions to the anonymous FTP user, such as write access to critical directories or the ability to execute commands. This allows an attacker to upload malicious files, such as shell scripts or compiled binaries, and then execute them through the FTP service. The root cause is a lack of proper input validation, privilege separation, and secure default configurations within the anon.ftp script. The script likely fails to restrict the anonymous user's ability to upload and execute files, creating a direct path for remote code execution. This is further exacerbated by the age of the vulnerability, as modern security practices were not as prevalent when the script was created.
Due to the age of the vulnerability, it's likely targeted by various threat actors. While specific APT attribution is difficult, any actor seeking to compromise legacy systems would likely leverage this. This vulnerability is not listed on the CISA KEV at this time, but its potential impact warrants consideration.
Monitor FTP server logs for suspicious activity, such as the upload of executable files or the execution of commands by the anonymous FTP user.
Analyze network traffic for FTP connections to the vulnerable system, especially those using anonymous credentials.
Review system logs for unusual processes or file modifications related to the FTP service or the anonymous FTP user's home directory.
Implement file integrity monitoring to detect unauthorized changes to critical system files.
Use a vulnerability scanner to identify systems with insecure FTP configurations.
Disable anonymous FTP access if it is not required. This is the most effective mitigation.
If anonymous FTP is required, reconfigure the service to restrict the anonymous user's permissions. Specifically, ensure that the anonymous user cannot write to or execute files in critical directories.
Implement strong password policies for all user accounts, including the FTP user.
Regularly update the AIX operating system and all installed software with the latest security patches.
Review and harden the FTP configuration file (e.g., ftpd.conf) to enforce security best practices.
Use a network intrusion detection/prevention system (IDS/IPS) to monitor for and block suspicious FTP traffic.
Implement two-factor authentication (2FA) for all user accounts, if possible.