CVE-2021-4189
MEDIUMCVSS 5.3/10EPSS 2.51%
Last modified
CVE-2021-4189 is a medium-severity vulnerability rated 5.3/10 on the CVSS scale. 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. EPSS estimates a 2.51% chance of exploitation in the next 30 days.
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.
Metrics
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
Weakness Enumeration
Affected Software
| Vendor | Product | Versions |
|---|---|---|
| Python | Python | >= 3.6.0, < 3.6.14 |
| Python | Python | >= 3.7.0, < 3.7.11 |
| Python | Python | >= 3.8.0, < 3.8.9 |
| Python | Python | >= 3.9.0, < 3.9.3 |
| Python | Python | 3.10.0 |
| Debian | Debian Linux | 10.0 |
| Debian | Debian Linux | 11.0 |
| Redhat | Software Collections | All versions |
| Redhat | Enterprise Linux | 8.0 |
| Netapp | Ontap Select Deploy Administration Utility | All versions |
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://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://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
Timeline
- Published
- Last Modified
- Status
- Modified
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 score of 5.3/10 (MEDIUM severity). The EPSS model estimates a 2.51% probability of exploitation in the next 30 days.
How do I fix CVE-2021-4189?
Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.
How Strix Helps
- How Strix found a critical auth bypass in etcdStrix autonomously discovered a critical authentication bypass in etcd, later designated CVE-2026-33413.
- Autonomous PentestingAI agents that find and validate exploitable vulnerabilities like this one across your applications.
- PR ReviewsPentest every pull request so vulnerable code is caught before it ships to production.
- AI Penetration TestingHow AI-driven penetration testing continuously covers your attack surface.
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