CVE-2021-4189

Name: CVE-2021-4189
Creator: NVD / NIST
Published: 2022-08-24T16:15:09.827+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 5.3/10EPSS 2.51%

Last modified Jun 17, 2026

CVE-2021-4189 is a medium-severity vulnerability rated 5.3/10 on the CVSS scale. 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. EPSS estimates a 2.51% chance of exploitation in the next 30 days.

Description

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.

Metrics

CVSS 3.1

5.3/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

EPSS Probability

2.51%

82.7th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Vendor	Product	Versions
Python	Python	>= 3.6.0, < 3.6.14
Python	Python	>= 3.7.0, < 3.7.11
Python	Python	>= 3.8.0, < 3.8.9
Python	Python	>= 3.9.0, < 3.9.3
Python	Python	3.10.0
Debian	Debian Linux	10.0
Debian	Debian Linux	11.0
Redhat	Software Collections	All versions
Redhat	Enterprise Linux	8.0
Netapp	Ontap Select Deploy Administration Utility	All versions

References

https://access.redhat.com/security/cve/CVE-2021-4189Third Party Advisory
https://bugs.python.org/issue43285Patch, Vendor Advisory
https://bugzilla.redhat.com/show_bug.cgi?id=2036020Issue Tracking, Patch, Third Party Advisory
https://github.com/python/cpython/commit/0ab152c6b5d95caa2dc1a30fa96e10258b5f188ePatch, Third Party Advisory
https://lists.debian.org/debian-lts-announce/2023/05/msg00024.html
https://lists.debian.org/debian-lts-announce/2023/06/msg00039.html
https://python-security.readthedocs.io/vuln/ftplib-pasv.htmlPatch, Third Party Advisory
https://security-tracker.debian.org/tracker/CVE-2021-4189Third Party Advisory
https://security.netapp.com/advisory/ntap-20221104-0004/Third Party Advisory
https://access.redhat.com/security/cve/CVE-2021-4189Third Party Advisory
https://bugs.python.org/issue43285Patch, Vendor Advisory
https://bugzilla.redhat.com/show_bug.cgi?id=2036020Issue Tracking, Patch, Third Party Advisory
https://github.com/python/cpython/commit/0ab152c6b5d95caa2dc1a30fa96e10258b5f188ePatch, Third Party Advisory
https://lists.debian.org/debian-lts-announce/2023/05/msg00024.html
https://lists.debian.org/debian-lts-announce/2023/06/msg00039.html
https://lists.debian.org/debian-lts-announce/2024/12/msg00000.html
https://python-security.readthedocs.io/vuln/ftplib-pasv.htmlPatch, Third Party Advisory
https://security-tracker.debian.org/tracker/CVE-2021-4189Third Party Advisory
https://security.netapp.com/advisory/ntap-20221104-0004/Third Party Advisory

Timeline

Published: Aug 24, 2022
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-4189?

How severe is CVE-2021-4189?

CVE-2021-4189 has a CVSS score of 5.3/10 (MEDIUM severity). The EPSS model estimates a 2.51% probability of exploitation in the next 30 days.

How do I fix CVE-2021-4189?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-4189?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST