Why Python's Requests Module Triggers Cloudflare Security Checks

Apr 2, 2024 ยท 3 min read

When making HTTP requests to websites protected by Cloudflare, you may notice that using Python's popular Requests module sometimes triggers Cloudflare bot mitigation or security checks, while using Python's built-in urllib module does not.

The Difference Between Requests and urllib

The key difference lies in how each module identifies itself to servers.

The Requests module sets a default User-Agent string that contains the text "Python/Requests", clearly identifying it as a Python script using Requests.

Meanwhile, urllib uses a more generic User-Agent like Python-urllib/3.x, which can seem like a regular web browser and does not stand out as much.

Cloudflare and other security services are more likely to flag Requests because it openly identifies as an automation script, while urllib flies under the radar better.

Why Cloudflare Flags Requests

Cloudflare provides DDoS protection and bot mitigation among its services. When Requests openly identifies itself, the Cloudflare firewall is more likely to view it as a potential malicious bot rather than a regular web browser.

As a result, it may trigger visitor challenges like CAPTCHAs, JavaScript exams, or blocking.

Meanwhile, urllib appears like a typical web visitor, so it does not raise the same level of concerns for bot-like activity.

Solutions: Spoofing User-Agent

If you wish to continue using Requests but want to avoid triggering Cloudflare, one option is to override the default Requests user-agent with a more generic one:

import requests

headers = {'User-Agent': 'My-App/1.0'}

r = requests.get(url, headers=headers)

This makes your script less identifiable as using Requests specifically. Just be aware that completely masquerading your traffic may violate terms of service. A custom user agent identifying as your own application may be allowed, but spoofing a browser entirely could still be an issue.

Alternatives to Requests

Another option is to switch out Requests to an alternative HTTP library like:

  • urllib - Python's built-in HTTP client already discussed
  • httpx - Fully featured HTTP client for Python 3
  • aiohttp - Asynchronous HTTP client for use with asyncio/async
  • These modules have different default user agents and behavior that may avoid triggering Cloudflare protections quite as often.

    Why Using Requests May Still Make Sense

    While the above discusses why Requests triggers security checks and some alternative solutions, there are good reasons you may still want to use it regardless:

  • Requests is very developer-friendly and intuitive API
  • Supports many advanced HTTP features like sessions and authentication out of the box
  • Very popular library with great community support resources
  • Actively maintained and improved unlike urllib
  • My recommendation is to try adjusting the user agent first while keeping Requests, which solves the security checks for many. Only switch libraries if that does not work for your particular use case.

    Key Takeaways

  • Requests openly identifies as Python/Requests causing Cloudflare to flag it
  • urllib has a generic user agent that flies under the radar
  • Solutions are to spoof the Requests user agent or use alternate libraries
  • Requests remains an excellent choice for most purposes
  • Hopefully this gives you a better understanding of why Requests may trigger security providers like Cloudflare and helps you resolve the issue!

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