Internal port scanning via trusted PASV address
Published Aug 24, 2022 · Updated Dec 17, 2025
SSRF in CPython ftplib before 3.6.14, 3.7.11, 3.8.9, 3.9.3, or 3.10.0 allows remote attackers to probe client-side TCP ports. FTP.makepasv parses an IPv4 host and port from the PASV reply and connects to that server-supplied host instead of the established control peer. Exploitation requires a client to use passive mode with an attacker-controlled FTP server; the consequence is TCP port probing from the client's network position.
Summary
What happened
SSRF in CPython ftplib before 3.6.14, 3.7.11, 3.8.9, 3.9.3, or 3.10.0 allows remote attackers to probe client-side TCP ports. FTP.makepasv parses an IPv4 host and port from the PASV reply and connects to that server-supplied host instead of the established control peer. Exploitation requires a client to use passive mode with an attacker-controlled FTP server; the consequence is TCP port probing from the client's network position.
The record
- CVE
- CVE-2021-4189
- Published
- Aug 24, 2022
- Updated
- Dec 17, 2025
- Vendor
- Python Software Foundation
- Product
- CPython
- Classifications
- CWE-252, T1046
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Aug 24, 2022CVE publishedPublication date reported by the CVE source.
- Dec 17, 2025Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=Fixed in python 3.6.14, python 3.7.11, python 3.8.9, python 3.9.3, python 3.10.0
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
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Public exploit references
No public exploit references are available in this record.
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Technologies
Your stack
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Your stack
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