Sandbox URL Creation

[pixeebot]

This codemod sandboxes calls to requests.get to be more resistant to Server-Side Request Forgery (SSRF) attacks.

Most of the time when you make a GET request to a URL, you're intending to reference an HTTP endpoint, like an internal microservice. However, URLs can point to local file system files, a Gopher stream in your local network, a JAR file on a remote Internet site, and all kinds of other unexpected and undesirable outcomes. When the URL values are influenced by attackers, they can trick your application into fetching internal resources, running malicious code, or otherwise harming the system.
Consider the following code for a Flask app:

from flask import Flask, request
import requests

app = Flask(__name__)

@app.route("/request-url")
def request_url():
    url = request.args["loc"]
    resp = requests.get(url)
    ...

In this case, an attacker could supply a value like "http://169.254.169.254/user-data/" and attempt to access user information.

Our changes introduce sandboxing around URL creation that force developers to specify some boundaries on the types of URLs they expect to create:

  from flask import Flask, request
- import requests
+ from security import safe_requests

  app = Flask(__name__)

  @app.route("/request-url")
  def request_url():
    url = request.args["loc"]
-   resp = requests.get(url)
+   resp = safe_requests.get(url)
    ...

This change alone reduces attack surface significantly because the default behavior of safe_requests.get raises a SecurityException if
a user attempts to access a known infrastructure location, unless specifically disabled.

If you have feedback on this codemod, please let us know!

F.A.Q.

Why does this codemod require a Pixee dependency?

We always prefer to use built-in Python functions or one from a well-known and trusted community dependency. However, we cannot find any such control. If you know of one, please let us know.

Why is this codemod marked as Merge After Cursory Review?

By default, the protection only weaves in 2 checks, which we believe will not cause any issues with the vast majority of code:

1. The given URL must be HTTP/HTTPS.
2. The given URL must not point to a "well-known infrastructure target", which includes things like AWS Metadata Service endpoints, and internal routers (e.g., 192.168.1.1) which are common targets of attacks.

However, on rare occasions an application may use a URL protocol like "file://" or "ftp://" in backend or middleware code.

If you want to allow those protocols, change the incoming PR to look more like this and get the best security possible:

-resp = requests.get(url)
+resp = safe_requests.get(url, allowed_protocols=("ftp",))

Dependency Updates

This codemod relies on an external dependency. However, we were unable to automatically add the dependency to your project.

This library holds security tools for protecting Python API calls.

There are a number of places where Python project dependencies can be expressed, including setup.py, pyproject.toml, setup.cfg, and requirements.txt files. You may need to manually add this dependency to the proper location in your project.

Manual Installation

For setup.py:

 install_requires=[
+    "security==1.2.1",
 ],

For pyproject.toml (using setuptools):

 [project]
 dependencies = [
+    "security==1.2.1",
 ]

For setup.cfg:

 [options]
 install_requires =
+    security==1.2.1

For requirements.txt:

+security==1.2.1

For more information on adding dependencies to setuptools projects, see the setuptools documentation.

If you are using another build system, please refer to the documentation for that system to determine how to add dependencies.

More reading

• https://github.com/pixee/python-security/blob/main/src/security/safe_requests/api.py
• https://portswigger.net/web-security/ssrf
• https://cheatsheetseries.owasp.org/cheatsheets/Server_Side_Request_Forgery_Prevention_Cheat_Sheet.html
• https://www.rapid7.com/blog/post/2021/11/23/owasp-top-10-deep-dive-defending-against-server-side-request-forgery/
• https://blog.assetnote.io/2021/01/13/blind-ssrf-chains/

I have additional improvements ready for this repo! If you want to see them, leave the comment:

@pixeebot next

... and I will open a new PR right away!

Powered by: pixeebot (codemod ID: pixee:python/url-sandbox)

[pixeebot]

I'm confident in this change, and the CI checks pass, too!

If you see any reason not to merge this, or you have suggestions for improvements, please let me know!

[pixeebot]

This change may not be a priority right now, so I'll close it. If there was something I could have done better, please let me know!

You can also customize me to make sure I'm working with you in the way you want.