CVE-2021-4189
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.
Does this matter?
Lower severity and a low EPSS score (3.41%). Track it; it rarely justifies an emergency change on its own.
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.
- CVSS 3.1
- 5.3 MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
- EPSS
- 3.41% probability · 89th percentile
- Public exploits
- None in Exploit-DB
- CISA KEV
- Not listed
- Weakness
- CWE-252
- Affected
- python/python · debian/debian linux · redhat/software collections · redhat/enterprise linux · netapp/ontap select deploy administration utility
- Source
- secalert@redhat.com
EPSS 3.4% since 26 October 2026; no change recorded yet. Points are recorded when the score first appears and whenever it moves by a percentage point or more.
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
- https://cert-portal.siemens.com/productcert/html/ssa-398330.html
Source: NVD record, EPSS from FIRST.org, KEV from CISA, exploits from Exploit-DB. Refreshed daily. Download this record as JSON.