CVE-2021-4189A flaw was found in Python, specifically in the FTP (File Transfer Protocol) client library in PASV (passive) mode. The issue is how the…
- 5.3MediumCVSS base score
- 3.6%Exploitation in 30 daysEPSS · top 10% of all CVEs
- NoKnown exploitednot in CISA's KEV catalog
- NonePublic exploitsnone known yet
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.
Timeline
ID reserved
By redhat
- 8 months later
· 8 months later
Published
- 4 years later
· 4 years later
Record updated
Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| CISA-ADPADP (enrichment) | 3.1 | Medium5.3 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N |
| NVDNVD · Modified | 3.1 | Medium5.3 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N |
- EPSS (exploitation in 30 days)
- 3.6% · top 10% of all CVEs (14 Nov 2026)
- CISA SSVC
- Exploitation: none · Automatable: yes · Technical impact: partial
The list uses the assigner's score when there is one, then CISA's, then NVD's: Medium 5.3.
Affected products
python
- affected Fixed in python 3.6.14, python 3.7.11, python 3.8.9, python 3.9.3, python 3.10.0
References
References12
- https://bugs.python.org/issue43285 (opens in a new tab)x_transferred
- https://python-security.readthedocs.io/vuln/ftplib-pasv.html (opens in a new tab)x_transferred
- https://github.com/python/cpython/commit/0ab152c6b5d95caa2dc1a30fa96e10258b5f188e (opens in a new tab)x_transferred
- https://security-tracker.debian.org/tracker/CVE-2021-4189 (opens in a new tab)x_transferred
- https://bugzilla.redhat.com/show_bug.cgi?id=2036020 (opens in a new tab)x_transferred
- https://access.redhat.com/security/cve/CVE-2021-4189 (opens in a new tab)x_transferred
- https://security.netapp.com/advisory/ntap-20221104-0004/ (opens in a new tab)x_transferred
- [debian-lts-announce] 20230524 [SECURITY] [DLA 3432-1] python2.7 security update (opens in a new tab)mailing-listx_transferred
- [debian-lts-announce] 20230630 [SECURITY] [DLA 3477-1] python3.7 security update (opens in a new tab)mailing-listx_transferred
- https://lists.debian.org/debian-lts-announce/2024/12/msg00000.html (opens in a new tab)
- https://cert-portal.siemens.com/productcert/html/ssa-398330.html (opens in a new tab)
- https://cert-portal.siemens.com/productcert/html/ssa-457936.html (opens in a new tab)
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- EUVD EUVD-2021-34049 (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisories (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://cveledger.app/cve/CVE-2021-4189)Record last updated .