CVE-2021-4189A flaw was found in Python, specifically in the FTP (File Transfer Protocol) client library in PASV (passive) mode.
Updated under an hour ago ()
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It affects Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP and 7 other products. Add what you run to find out whether that includes you.
No exploitation reported and no EPSS estimate yet.
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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.
- CVSS
- 5.3 MEDIUM (v3.1, CISA ADP)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
- Weakness (CWE)
- CWE-252
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- Not loaded for this CVE
- Assigned by
- redhat
- NVD analysis
- Modified
- Record last updated
- Oct 14, 2026
- First seen by InfoSec Signals
- Oct 14, 2026
Affected products
Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP siemens:simatic_s7_1500_cpu_1518_4_pn_dp_mfp (from the name) | from V3.1.0 before V3.1.5 | CISA ADP |
Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP siemens:simatic_s7_1500_cpu_1518f_4_pn_dp_mfp (from the name) | from V3.1.0 before V3.1.5 | CISA ADP |
Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP siemens:siplus_s7_1500_cpu_1518_4_pn_dp_mfp (from the name) | from V3.1.0 before V3.1.5 | CISA ADP |
python python python:python | from 3.6.0 before 3.6.14; from 3.7.0 before 3.7.11; from 3.8.0 before 3.8.9; from 3.9.0 before 3.9.3; 3.10.0 | NVD |
debian debian_linux debian:debian_linux | 10.0; 11.0 | NVD |
redhat software_collections redhat:software_collections | all versions | NVD |
redhat enterprise_linux redhat:enterprise_linux | 8.0 | NVD |
netapp ontap_select_deploy_administration_utility netapp:ontap_select_deploy_administration_utility | all versions | NVD |
References
- https://bugs.python.org/issue43285patch, vendor-advisory
- https://python-security.readthedocs.io/vuln/ftplib-pasv.htmlpatch, third-party-advisory
- https://github.com/python/cpython/commit/0ab152c6b5d95caa2dc1a30fa96e10258b5f188epatch, third-party-advisory
- https://security-tracker.debian.org/tracker/CVE-2021-4189third-party-advisory
- https://bugzilla.redhat.com/show_bug.cgi?id=2036020issue-tracking, patch, third-party-advisory
- https://access.redhat.com/security/cve/CVE-2021-4189third-party-advisory
- https://security.netapp.com/advisory/ntap-20221104-0004/third-party-advisory
- https://lists.debian.org/debian-lts-announce/2023/05/msg00024.htmlmailing-list
- https://lists.debian.org/debian-lts-announce/2023/06/msg00039.htmlmailing-list
- https://lists.debian.org/debian-lts-announce/2024/12/msg00000.html
- https://cert-portal.siemens.com/productcert/html/ssa-398330.html
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.