Monsters in the Middleboxes: Introducing Two New Tools for Detecting HTTPS Interception

The practice of HTTPS interception continues to be commonplace on the Internet. HTTPS interception has encountered scrutiny, most notably in the 2017 study “The Security Impact of HTTPS Interception” and the United States Computer Emergency Readiness Team (US-CERT)  warning that the technique weakens security. In this blog post, we provide a brief recap of HTTPS interception and introduce two new tools:

1. MITMEngine, an open-source library for HTTPS interception detection, and
2. MALCOLM, a dashboard displaying metrics about HTTPS interception we observe on Cloudflare’s network.

In a basic HTTPS connection, a browser (client) establishes a TLS connection directly to an origin server to send requests and download content. However, many connections on the Internet are not directly from a browser to the server serving the website, but instead traverse through some type of proxy or middlebox (a “monster-in-the-middle” or MITM). There are many reasons for this behavior, both malicious and benign.

Types of HTTPS Interception, as Demonstrated by Various Monsters in the Middle

One common HTTPS interceptor is TLS-terminating forward proxies. (These are a subset of all forward proxies; non-TLS-terminating forward proxies forward TLS connections without any ability to inspect encrypted traffic). A TLS-terminating forward proxy sits Continue reading

Tracing Soon-to-Expire Federal .gov Certificates with CT Monitors

As of December 22, 2018, parts of the US Government have “shut down” because of a lapse in appropriation. The shutdown has caused the furlough of employees across the government and has affected federal contracts. An unexpected side-effect of this shutdown has been the expiration of TLS certificates on some .gov websites. This side-effect has emphasized a common issue on the Internet: the usage of expired certificates and their erosion of trust.

For an entity to provide a secure website, it needs a valid TLS certificate attached to the website server. These TLS certificates have both start dates and expiry dates. Normally certificates are renewed prior to their expiration. However, if there’s no one to execute this process, then websites serve expired certificates--a poor security practice.

This means that people looking for government information or resources may encounter alarming error messages when visiting important .gov websites:

The content of the website hasn’t changed; it’s just the cryptographic exchange that’s invalid (an expired certificate can’t be validated). These expired certificates present a trust problem. Certificate errors often dissuade people from accessing a website, and imply that the site is not to be trusted. Browsers purposefully make it difficult to continue to Continue reading

Real URLs for AMP Cached Content Using Cloudflare Workers

Today, we’re excited to announce our solution for arguably the biggest issue affecting Accelerated Mobile Pages (AMP): the inability to use real origin URLs when serving AMP-cached content. To allow AMP caches to serve content under its origin URL, we implemented HTTP signed exchanges, which extend authenticity and integrity to content cached and served on behalf of a publisher. This logic lives on Cloudflare Workers, meaning that adding HTTP signed exchanges to your content is just a simple Workers application away. Publishers on Cloudflare can now take advantage of AMP performance and have AMP caches serve content with their origin URLs. We're thrilled to use Workers as a core component of this solution.

HTTP signed exchanges are a crucial component of the emerging Web Packaging standard, a set of protocols used to package websites for distribution through optimized delivery systems like Google AMP. This announcement comes just in time for Chrome Dev Summit 2018, where our colleague Rustam Lalkaka spoke about our efforts to advance the Web Packaging standard.

What is Web Packaging and Why Does it Matter?

You may already see the need for Web Packaging on a daily basis. On your smartphone, perhaps you’ve searched for Christmas Continue reading