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CVE-2021-4189

MEDIUM
5.3
CVSS Score
Published: August 24, 2022 at 12:00 AM UTC
Updated: October 14, 2026 at 11:16 AM UTC
5 products affected across 4 vendorsDebian LinuxEnterprise LinuxPython

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Severity
MEDIUM5.3
Exploit prediction
EPSS 3%
SSVC
No known exploit

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

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Debian Linux· Debiandrupal
95%
10.011.0
ONTAP Select Deploy administration utility· NetApp
95%
All versions
Python· Python
95%
3.6.0 ≤ v < 3.6.143.7.0 ≤ v < 3.7.113.8.0 ≤ v < 3.8.93.9.0 ≤ v < 3.9.33.10.0
Vendor states this is fixed in 3.6.14 (unaffected)
Affected range stops below 3.7.11, so it looks safe — our inference, not a vendor statement
Affected range stops below 3.8.9, so it looks safe — our inference, not a vendor statement
Affected range stops below 3.9.3, so it looks safe — our inference, not a vendor statement
Enterprise Linux· Red Hatrpm
95%
8.0
Software Collections· Red Hatrpm
95%
All versions

References (11)

Third Party Advisory
Source: [email protected]
https://access.redhat.com/security/cve/CVE-2021-4189
PatchVendor Advisory
Source: [email protected]
https://bugs.python.org/issue43285
Issue TrackingPatchThird Party Advisory
Source: [email protected]
https://bugzilla.redhat.com/show_bug.cgi?id=2036020
PatchThird Party Advisory
Source: [email protected]
https://github.com/python/cpython/commit/0ab152c6b5d95caa2dc1a30fa96e10258b5f188e
Mailing List
Source: [email protected]
https://lists.debian.org/debian-lts-announce/2023/05/msg00024.html
Mailing List
Source: [email protected]
https://lists.debian.org/debian-lts-announce/2023/06/msg00039.html
PatchThird Party Advisory
Source: [email protected]
https://python-security.readthedocs.io/vuln/ftplib-pasv.html
Third Party Advisory
Source: [email protected]
https://security-tracker.debian.org/tracker/CVE-2021-4189

SSVC — Action Prioritization

SSVCNo known exploitAutomatablePartial impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

5.3MEDIUMCISA-ADP
Attack Vector
NETWORK
Complexity
LOW
Privileges
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
LOW
Integrity
NONE
Availability
NONE
Vector?

Quick Info

StatusMODIFIED
CWE
CWE-252

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