CVE Intelligence
Medium Logic error

CVE-2021-4189 — A flaw was found in Python, specifically in the FTP (File Transfer Protocol) client library in...

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 Aug 24, 2022 · Updated Oct 14, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP, GitHub Security Advisories · CNA: redhat

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.
How the score was calculated
  • EPSS 3.2% (30-day exploitation probability)+13
  • Technical severity (medium)+3
  • Automatable exploitation (SSVC)+3

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation
Not confirmed
Not in CISA KEV — an absence of record, not proof it is unexploited.
EPSS FIRST
3.2%
ahead of 88% of scored CVEs · Oct 14, 2026
Affects
Debian
Debian Linux and 4 more
CVSS base
5.3
Medium · 4 source(s)

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Exploitation
None
none · proof-of-concept · active
Automatable
Yes
can an attacker script the kill-chain steps
Technical impact
Partial
partial · total control of the vulnerable component

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

  1. Identify exposed assets running the affected vendor/product/version combinations (Debian Debian Linux, Netapp Ontap Select Deploy Administration Utility, Python Python…).
  2. The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
  3. Apply the fixed version or the patch documented under Remediation.
  4. Search available logs for exploit probes matching the vulnerability class (logic error), errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

VendorProductVersionsStatusSource
Debian Debian Linux version 10.0version 11.0 Vulnerable NIST National Vulnerability Database
Netapp Ontap Select Deploy Administration Utility versions not specified by the source Vulnerable NIST National Vulnerability Database
Python Python ≥ 3.6.0 and < 3.6.14≥ 3.7.0 and < 3.7.11≥ 3.8.0 and < 3.8.9≥ 3.9.0 and < 3.9.3version 3.10.0 Vulnerable NIST National Vulnerability Database
Red Hat Enterprise Linux version 8.0 Vulnerable NIST National Vulnerability Database
Red Hat Software Collections versions not specified by the source Vulnerable NIST National Vulnerability Database

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
None
Availability
None

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

ScoreVersionSeverityExpl.ImpactScored by
5.3 CVSS 3.1 Medium 3.9 1.4 nvd@nist.gov via NIST National Vulnerability Database
5.3 CVSS 3.1 Medium 3.9 1.4 134c704f-9b21-4f2e-91b3-4a467353bcc0 via NIST National Vulnerability Database
5.3 CVSS 3.1 Medium — — GitHub, Inc. via GitHub Security Advisories
5.3 CVSS 3.1 Medium — — CISA-ADP via CVE Program (cve.org) e CISA ADP
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N (score shown at the top: nvd@nist.gov)

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-252 · Unchecked Return Value

Other CVEs with this weakness →

EPSS over time FIRST

Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 3.20%

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

  • Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
web/proxy/WAF logsnetwork IDS/IPS

Timeline

What happened to this CVE, newest first.

  • 2026
  • SSVC assessment updated
    Oct 14, 2026 · CVE Program (cve.org) e CISA ADP
  • Record published
    Oct 14, 2026
  • Fix documented
    Oct 14, 2026 · NIST National Vulnerability Database
  • Affected products added · python/python, debian/debian linux, redhat/software collections, redhat/enterprise linux, netapp/ontap select deploy adm
    Oct 14, 2026 · NIST National Vulnerability Database
  • CVSS changed · 5.3
    Oct 14, 2026 · NIST National Vulnerability Database
  • Source status changed · → Modified
    Oct 14, 2026 · NIST National Vulnerability Database
  • Record created in this database
    Oct 14, 2026 · Alertas do Telegram
  • 2022
  • CVE published
    Aug 24, 2022 · redhat

Source activity

Repeated readings are counted rather than listed.

  • 2× References added · Oct 14, 2026 – Oct 14, 2026
  • 1× Official description updated · Oct 14, 2026 – Oct 14, 2026

References

14 on the record

Elsewhere on this site

Debian
every CVE for this vendor
Logic error
same class
CWE-252
other pages naming this weakness

Related CVEs (same products)

  • CVE-2026-104045 Sssd: sssd: denial of service via race condition in autofs responder 8d
  • CVE-2026-104046 Sssd: sssd: denial of service via incomplete identity provider authentication requests 8d
  • CVE-2026-104048 Sssd: sssd: authorization bypass via cross-domain username collision in hbac evaluation 8d
  • CVE-2026-104047 Sssd: sssd: information disclosure via query injection in entra id lookups 8d
  • CVE-2026-102558 Libsoup: libsoup: heap buffer overflow during websocket receive-buffer growth 16d
  • CVE-2026-102555 Libsoup: libsoup: heap buffer overflow via uninitialized length in data-uri base64 decoding 16d

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

  • No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
  • No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
  • No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2021-4189 is "A flaw was found in Python, specifically in the FTP (File Transfer Protocol) client library in...", rated Medium. It affects Debian Linux (Debian); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 5.3 describes technical severity. EPSS 3.20% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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