CVE-2021-4189 : Exploit Details and Defense Strategies

A flaw in Python's FTP client library in PASV mode allows an attacker to set up a malicious FTP server, tricking clients into connecting back to a specified IP and port, potentially leading to port scanning.

Understanding CVE-2021-4189

This CVE identifies a vulnerability in Python's FTP client library when operating in PASV (passive) mode.

What is CVE-2021-4189?

The flaw in Python's FTP client library allows malicious FTP servers to manipulate client connections, leading to potential port scanning activities.

The Impact of CVE-2021-4189

Exploitation of this vulnerability could result in unauthorized port scanning, enabling actions that were previously restricted.

Technical Details of CVE-2021-4189

This section outlines the specific technical aspects of CVE-2021-4189.

Vulnerability Description

The vulnerability lies in how Python's FTP client trusts the host in PASV responses by default, allowing for the setup of malicious FTP servers.

Affected Systems and Versions

Python versions affected include python 3.6.14, python 3.7.11, python 3.8.9, python 3.9.3, and python 3.10.0.

Exploitation Mechanism

Attackers can exploit this flaw to deceive FTP clients into connecting back to a designated IP address and port.

Mitigation and Prevention

To address CVE-2021-4189, implement the following security measures:

Immediate Steps to Take

Upgrade to the fixed Python versions: 3.6.14, 3.7.11, 3.8.9, 3.9.3, or 3.10.0.
Verify and restrict FTP connections to trusted servers.

Long-Term Security Practices

Regularly update software to patched versions.
Monitor network traffic for suspicious activities.

Patching and Updates

Stay informed about security patches and apply them promptly to mitigate potential risks.