CVE-2021-4189: Debian Linux

Medium severity, CVSS 5.3. EPSS: 3.2% chance of exploitation in the next 30 days.

A flaw was found in Python, specifically in the FTP (File Transfer Protocol) client library in PASV (passive) mode. The issue is how the FTP client trusts the host from the PASV response by default. This flaw allows an attacker to set up a malicious FTP server that can trick FTP clients into connecting back to a given IP address and port. This vulnerability could lead to FTP client scanning ports, which otherwise would not have been possible.

Affected products

• Debian Debian Linux: version 10.0 only; version 11.0 only
• Netapp Ontap Select Deploy Administration Utility: affected versions not specified
• Python Python: from 3.6.0, before 3.6.14 (fixed in 3.6.14); from 3.7.0, before 3.7.11 (fixed in 3.7.11); from 3.8.0, before 3.8.9 (fixed in 3.8.9); from 3.9.0, before 3.9.3 (fixed in 3.9.3); version 3.10.0 only
• Red Hat Enterprise Linux: version 8.0 only
• Red Hat Software Collections: affected versions not specified

Published 2022-08-24. Last modified 2026-06-17.