What’s Vulnerable › Vulnerabilities
CVE-2021-37533: Apache Commons Net's FTP client trusts the host from PASV response by default
- Severity: medium (CVSS 6.5 v3.1)
- Exploited in the wild: not listed in CISA KEV
- EPSS: 2.1% probability of exploitation in the next 30 days
- Public exploit or detection template: none known
- Published: 2022-12-03 · updated 2026-06-17
- Weakness: CWE-20
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 products
- Apache Commons Net: before 3.9.0 — fixed in 3.9.0
- Debian Linux: 10.0, 11.0
How to fix
Upgrade to a fixed version: Apache Commons Net 3.9.0. Check the vendor advisory for mitigations.
References
- http://www.openwall.com/lists/oss-security/2022/12/03/1
- https://lists.apache.org/thread/o6yn9r9x6s94v97264hmgol1sf48mvx7
- https://lists.debian.org/debian-lts-announce/2022/12/msg00038.html
- https://www.debian.org/security/2022/dsa-5307
- http://www.openwall.com/lists/oss-security/2022/12/03/1
- https://lists.apache.org/thread/o6yn9r9x6s94v97264hmgol1sf48mvx7
- https://lists.debian.org/debian-lts-announce/2022/12/msg00038.html
- https://www.debian.org/security/2022/dsa-5307
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