CVE-2021-4189

CVE-2021-4189 is a medium-severity vulnerability in Redhat Software Collections with a CVSS 3.x base score of 5.3. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-252.

Key facts

• Severity: Medium (CVSS 3.x base score 5.3)
• EPSS exploit prediction: 3% (83rd percentile)
• Actively exploited: Not listed in CISA KEV
• Weakness: CWE-252
• Affected product: Redhat Software Collections
• Published: 2022-08-24
• Last modified: 2026-06-17

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.

Frequently asked questions

What is CVE-2021-4189?

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.

How severe is CVE-2021-4189?

CVE-2021-4189 has a CVSS 3.x base score of 5.3, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity none, and availability none.

Is CVE-2021-4189 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 3% (83rd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-4189?

CVE-2021-4189 primarily affects Redhat Software Collections. In total, 7 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-4189?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2021-4189 published?

CVE-2021-4189 was published on 2022-08-24 and last updated on 2026-06-17.

References

• https://access.redhat.com/security/cve/CVE-2021-4189
• https://bugs.python.org/issue43285
• https://bugzilla.redhat.com/show_bug.cgi?id=2036020
• https://github.com/python/cpython/commit/0ab152c6b5d95caa2dc1a30fa96e10258b5f188e
• 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.html
• https://security-tracker.debian.org/tracker/CVE-2021-4189
• https://security.netapp.com/advisory/ntap-20221104-0004/
• https://lists.debian.org/debian-lts-announce/2024/12/msg00000.html

Affected products (7)

• cpe:2.3:a:python:python:*:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:3.10.0:-:*:*:*:*:*:*
• cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:*
• cpe:2.3:o:debian:debian_linux:11.0:*:*:*:*:*:*:*
• cpe:2.3:a:redhat:software_collections:-:*:*:*:*:*:*:*
• cpe:2.3:o:redhat:enterprise_linux:8.0:*:*:*:*:*:*:*
• cpe:2.3:a:netapp:ontap_select_deploy_administration_utility:-:*:*:*:*:*:*:*

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Other CWE-252 vulnerabilities

• CVE-2025-66565 — Critical (CVSS 9.8): Fiber Utils is a collection of common functions created for Fiber. In versions 2.0.0-rc.3 and below, when the system's…
• CVE-2021-38171 — Critical (CVSS 9.8): adts_decode_extradata in libavformat/adtsenc.c in FFmpeg 4.4 does not check the init_get_bits return value, which is a…
• CVE-2021-26955 — Critical (CVSS 9.8): An issue was discovered in the xcb crate through 2021-02-04 for Rust. It has a soundness violation because…
• CVE-1999-0199 — Critical (CVSS 9.8): manual/search.texi in the GNU C Library (aka glibc) before 2.2 lacks a statement about the unspecified tdelete return…
• CVE-2019-15900 — Critical (CVSS 9.8): An issue was discovered in slicer69 doas before 6.2 on certain platforms other than OpenBSD. On platforms without…
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Threat intelligence

Threat-intel indicators referencing this CVE:

• 141.109.168.26 (ipv4-addr)
• 141.109.168.107 (ipv4-addr)
• 120.28.109.188 (ipv4-addr)
• 120.224.15.67 (ipv4-addr)
• 141.109.168.51 (ipv4-addr)
• 222.88.237.152 (ipv4-addr)
• 160.202.46.190 (ipv4-addr)