CVE Catalog

CVE-2021-4189

MediumCVSS 5.3
Published: Updated: Translated: NVD NIST

Exploitation Probability (EPSS)

High risk
3.20%

88th percentile - higher than 88% of all known CVEs

Summary

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.

Risk Assessment

An attacker can use the FTP client to scan ports in the internal network, potentially revealing information about services and enabling further attacks.

Recommendation

Update Python to a patched version. Consider changing the default FTP client behavior to not trust the host from PASV response without verification.

Other vulnerabilities in Python

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Original NVD description (English source)

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.

Vulnerability data from NVD (NIST) · CISA KEV · EPSS