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.

Weakness

The product does not check the return value from a method or function, which can prevent it from detecting unexpected states and conditions.

Affected Software

Potential Mitigations

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://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://lists.debian.org/debian-lts-announce/2024/12/msg00000.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/