CVE-2021-37533

Apache Commons Net's FTP client trusts the host from PASV response by default

MEDIUM
6.5
CVSS Score
Published: December 3, 2022 at 12:00 AM UTC
Updated: June 17, 2026 at 04:00 AM UTC
2 products affected across 2 vendorsDebian LinuxCommons .NET

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Severity
MEDIUM6.5
Exploit prediction
EPSS 2%
SSVC
No known exploit

Description

Prior to Apache Commons Net 3.9.0, Net's FTP client trusts the host from PASV response by default. A malicious server can redirect the Commons Net code to use a different host, but the user has to connect to the malicious server in the first place. This may lead to leakage of information about services running on the private network of the client. The default in version 3.9.0 is now false to ignore such hosts, as cURL does. See https://issues.apache.org/jira/browse/NET-711.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

v < 3.9.0Apache Commons Net ≤ v < 3.9.0
Affected range stops below 3.9.0, so it looks safe — our inference, not a vendor statement

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

SSVC — Action Prioritization

SSVCNo known exploitNot automatablePartial impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

6.5MEDIUMCISA-ADP
Attack Vector
NETWORK
Complexity
LOW
Privileges
NONE
User Interaction
REQUIRED
Scope
UNCHANGED
Confidentiality
HIGH
Integrity
NONE
Availability
NONE
Vector?

Quick Info

StatusMODIFIED
CWE
CWE-20

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