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Vulnerabilities

Vulnerability · CVE-2021-4189

A flaw was found in Python, specifically in the FTP (File Transfer Protocol) client library in PASV (passive) mode.

Published Aug 24, 2022 · catalog updated Oct 14, 2026 · A flaw was found

Check if you run it

No confirmed exploitation is on record for CVE-2021-4189. EPSS is 3.20%. Act only if a listed version of A flaw was found is installed.

Gaps on this record

  • The stored product name is a package slug. The name on this page is taken from the title (A flaw was found).
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
Medium5.3
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
3.20%
Remediation
Advisory link
Affected products
cpe debian/debian linux · cpe netapp/ontap select deploy administration utility · cpe python/python · cpe redhat/software collections

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.

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • cpe debian/debian linux10.0
  • cpe debian/debian linux11.0
  • cpe netapp/ontap select deploy administration utilityversion unspecified
  • cpe python/python3.10.0
  • cpe redhat/software collectionsversion unspecified

How to fix CVE-2021-4189

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2021-4189. EPSS is 3.20%. Act only if a listed version of A flaw was found is installed.

Which versions are affected?

Compare what you have installed with debian/debian linux 10.0; debian/debian linux 11.0. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-252: Unchecked Return Value. EPSS 3.20%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. Aug 24, 2022 · NIST NVD

    Detected

    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,

  2. Oct 14, 2026 · NIST NVD

    Updated

    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,

Sources

  • CVE.orgVulnerability recordCVE-2021-4189

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2021-4189

    30-day exploitation probability 3.2%

    first.org
  • NIST NVDVulnerability recordCVE-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

    nvd.nist.gov

References

Freshness

Last verified in this catalog Oct 16, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.