🛡️ CVE-2021-4189 — libpython

🟡 CVSS 5.0 — Medium ✅ No Known Exploit OSV
5.0
CVSS Score
0 Low4 Medium7 High9 Critical10

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.

Affected software

CVE-2021-4189 is recorded against 3 packages.

  • libpython
  • python
  • python-min

Timeline and source

Published on 11 August 2025 and last revised on 6 November 2025. No public exploit is currently recorded for this entry. Record sourced from OSV.

References

access.redhat.com (Web)
bugs.python.org (Web)
bugzilla.redhat.com (Web)
github.com (Web)
lists.debian.org (Web)
lists.debian.org (Web)
nvd.nist.gov (Web)
python-security.readthedocs.io (Web)
security-tracker.debian.org (Web)
security.netapp.com (Web)
lists.debian.org (Web)

CVE-2021-4189 on other distributions

Each distribution ships its own build and its own fixed version. Pick the one you run:

Details

Severity MEDIUM
CVSS Score 5.0
CVSS Vector N/A
CWE N/A
Public Exploit ✅ No
Source OSV
Published 2025-08-11
Updated 2026-06-02
Modified 2025-11-06
Fix URL N/A

Affected Packages

Software From version Fixed in
libpython
python
python-min

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