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.
Advisories
Source ID Title
Debian DLA Debian DLA DLA-2919-1 python2.7 security update
Debian DLA Debian DLA DLA-3432-1 python2.7 security update
Debian DLA Debian DLA DLA-3477-1 python3.7 security update
Debian DLA Debian DLA DLA-3980-1 python3.9 security update
EUVD EUVD EUVD-2021-34049 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.
Ubuntu USN Ubuntu USN USN-5342-1 Python vulnerabilities
Ubuntu USN Ubuntu USN USN-5342-2 Python vulnerabilities
Ubuntu USN Ubuntu USN USN-6891-1 Python vulnerabilities
Fixes

Solution

No solution given by the vendor.


Workaround

No workaround given by the vendor.

History

Mon, 03 Nov 2025 22:30:00 +0000

Type Values Removed Values Added
References

cve-icon MITRE

Status: PUBLISHED

Assigner: redhat

Published:

Updated: 2025-11-03T21:45:21.395Z

Reserved: 2021-12-29T00:00:00.000Z

Link: CVE-2021-4189

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Modified

Published: 2022-08-24T16:15:09.827

Modified: 2025-11-03T22:15:54.013

Link: CVE-2021-4189

cve-icon Redhat

Severity : Moderate

Publid Date: 2021-12-21T00:00:00Z

Links: CVE-2021-4189 - Bugzilla

cve-icon OpenCVE Enrichment

No data.