White-listing Tor in CloudFlare with PowerShell

CloudFlare has been one of those technologies that has dramatically improved the Internet since its arrival. CloudFlare provides a number of amazing features, from DDOS protection, traffic analytics, performance optimizations and even free SSL! To top it all off, CloudFlare off the majority of their features for an amazing price – FREE!

Unfortunately, there are a group of users who have suffered with the rapid adaption of websites being protected by CloudFlare; Tor users. Whilst the majority of us receive the benefits of CloudFlare, it has made life for Tor users extremely miserable.

What is the issue with CloudFlare and Tor?

To understand the issues CloudFlare and Tor, we first need to understand how CloudFlare protects a website. When you visit a protected website, CloudFlare performs a risk assessment of your IP address. If CloudFlare decides that you are friendly, then you get to view the website. If it decides you are suspicious, then you will either be prompted with a CAPTCHA request or, in the extreme cases, it will deny access to the website.

The Tor is an interesting network, developed with the aim to protect privacy and defend against surveillance; the network has become a bit of a hive of scum and villainy. Due to the high use of Tor for malicious activity, CloudFlare is naturally suspicious of any connections coming from a Tor exit node, which results in a high risk assessment for all Tor users accessing protected websites.

A high risk assessment results in lots of CAPTCHA requests for Tor users to complete. Every protected page that a Tor user visits, will result in a CAPTCHA request, whilst most of us don’t mind completing these, consider how you would feel answering one every 15 to 20 minutes. It impacts productivity and your sanity.

What is the solution?

The trust of the matter is that there isn’t a simple solution, there isn’t a magic “trust Tor” button in the CloudFlare. It is down to individual website operators to white-list the Tor exit IP addresses; this isn’t trivial, requiring operators to maintain a white-list as the Tor network changes, adding new exit IP addresses that join the Tor network, whilst removing those that leave.

Now is the best time to point out the risks of white-listing. White-listing isn’t without its own risks! When you white-list an IP address in CloudFlare, you are telling it to ignore how risky the traffic coming from that address might be. Not all Tor users legitimately want to view the content of your website; some Tor users are malicious, they are out for blood. White-listing significantly changes the security protection of your site, and you need to be extremely aware of the risks it introduces.

Set and Forget White-Listing

Donncha O'Cearbhaill developed a Python based script with the aim of providing a “set and forget” mechanism for white-listing Tor exit IPs. Donncha’s Automatic CloudFlare Tor Exit Whitelister takes your CloudFlare API token and email address and does all the hard work. The script will grab the latest listing of the Tor exit IPs, and then updates CloudFlare’s white list as appropriate.

When I saw the script, my immediate reaction was “what an amazing idea”, my next was, “how could this be made more accessible to more website operators?

Turning to PowerShell

The obvious answer to encouraging more web site operators to white-list Tor exit nodes is to provide the process in more accessible formats. For Windows users, the best option is to provide the process as a PowerShell script.

So I sat down, learn some Python, and then worked on developing a PowerShell script with similar functionality as Donncha’s. This was a super fun and interesting process. In the end, I deliberately tried to stick a similar logic flow, similar parameters are supported (via parameter liases), and the scripts default output is similar. I added some additional verbose and debug options and added progress bars for long operations. I haven’t included support for specifying the CloudFlare API token and email address via environment variables.

The final result can be found over at GitHub, at https://github.com/poshsecurity/PowerShell-CloudFlare-Tor-Whitelist. All of the functionality is provided by the Set-CloudFlareWhiteList.ps1 script.

Please feel free to raise pull requests, issues, or provide any feedback that you may have.

Usage

I have included comment based help, with examples on how to make use of the script. There are three common usage methods.

1. Specifying a CloudFlare token and email. This will white-list exit node IP addresses across all of the domains in your CloudFlare account
2. Specifying a CloudFlare token, email and a DNS zone. This will white-list exit node IP addresses for a specific DNS zone.
3. Specify a Token, email and optionally a DNS zone, and the -ClearFlags parameter. Remove all Tor specific rules for all domains in your CloudFlare account, or for a specific DNS Zone.

Finishing Up

I want to thank Donncha for his work in developing the original Python script. Without his work, I wouldn’t have been able to develop mine.

If you want to find out more about CloudFlare, Troy Hunt has put together a terrific PluralSight course, Getting Started with CloudFlare™ Security. He covers the basics including migration, SSL configuration and even HSTS.

Kieran Jacobsen