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.

Published: 2022-08-24 Last update: 2025-12-17 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-4189 is rated Moderate Risk (48.6/100): CVSS Medium severity, with medium exploitation likelihood (EPSS 1.06%). Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2021-4189

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-03-04 0.73% 1.06% +0.33%
2 2026-03-01 1.06% 0.73% -0.33%
3 2026-02-14 — 1.06% —

Full EPSS history (23 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-4189

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
5.3 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:L)
Some sensitive info could get out, but not a total data dump.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:N)
Service keeps running; no real outage angle.
 3.9 1.4 [email protected]
5.3 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:L)
Some sensitive info could get out, but not a total data dump.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:N)
Service keeps running; no real outage angle.
 3.9 1.4 134c704f-9b21-4f2e-91b3-4a467353bcc0

Weakness enumeration for CVE-2021-4189

OS Trackers for CVE-2021-4189

vendor priority summary link
debian not yet assigned CVE-2021-4189 not yet assigned priority: Debian including 3 source packages (pypy3, python2.7, python3.9), 7 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 6, open 1. https://security-tracker.debian.org/tracker/CVE-2021-4189
redhat medium — https://access.redhat.com/security/cve/CVE-2021-4189
suse medium — https://www.suse.com/security/cve/CVE-2021-4189/
ubuntu medium CVE-2021-4189 medium priority: Ubuntu including 8 source packages (python2.7, python3.10, …), 120 status rows across 15 suites (bionic, focal, hirsute, impish, jammy, kinetic, lunar, mantic, noble, oracular, plucky, questing, trusty, upstream, xenial): DNE 90, released 14, not-affected 6, ignored 5, needed 3, needs-triage 2. https://ubuntu.com/security/CVE-2021-4189

Affected software / configurations for CVE-2021-4189

Vendor Product Version Raw CPE
python python >= 3.6.0, < 3.6.14 cpe:2.3:a:python:python:*:*:*:*:*:*:*:*
python python >= 3.7.0, < 3.7.11 cpe:2.3:a:python:python:*:*:*:*:*:*:*:*
python python >= 3.8.0, < 3.8.9 cpe:2.3:a:python:python:*:*:*:*:*:*:*:*
python python >= 3.9.0, < 3.9.3 cpe:2.3:a:python:python:*:*:*:*:*:*:*:*
python python 3.10.0 cpe:2.3:a:python:python:3.10.0:-:*:*:*:*:*:*
debian debian_linux 10.0 cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:*
debian debian_linux 11.0 cpe:2.3:o:debian:debian_linux:11.0:*:*:*:*:*:*:*
redhat software_collections — cpe:2.3:a:redhat:software_collections:-:*:*:*:*:*:*:*
redhat enterprise_linux 8.0 cpe:2.3:o:redhat:enterprise_linux:8.0:*:*:*:*:*:*:*
netapp ontap_select_deploy_administration_utility — cpe:2.3:a:netapp:ontap_select_deploy_administration_utility:-:*:*:*:*:*:*:*

References for CVE-2021-4189

cvelogic Threat Intelligence