# PSF-2021-5: ftplib should not use the host from the PASV response

> A malicious FTP server can force the client to probe internal network addresses via PASV response, enabling SSRF-like attacks.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 21 Feb 2021

## What is PSF-2021-5?

PSF-2021-5 is a server-side request forgery vulnerability, published on 21 Feb 2021. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

### Official description

The IPv4 address value returned from the server in response to the PASV
command should not be trusted. This prevents a malicious FTP server from
using the response to probe IPv4 address and port combinations on the
client network.

Instead of using the returned address, we use the IP address we're already
connected to. This is the strategy other ftp clients adopted, and matches
the only strategy available for the modern IPv6 EPSV command where the
server response must return a port number and nothing else.

## Which versions are affected by PSF-2021-5?


## How do I fix PSF-2021-5?

No fix has been published for PSF-2021-5 yet. Limit exposure of the affected software until one is available.

## Is PSF-2021-5 being exploited?

There is no known exploitation of PSF-2021-5 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for PSF-2021-5 and fix it if it is affected.

What it is: PSF-2021-5 is a server-side request forgery vulnerability, published on 21 Feb 2021. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of PSF-2021-5 in the wild and no public exploit code.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/PSF-2021-5/ (Markdown: https://insights.sbomify.com/PSF-2021-5/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/PSF-2021-5

---
From sbomify Insights: https://insights.sbomify.com/PSF-2021-5/
Summaries are generated and may contain mistakes; the official description above is the record.