http-desync-guardian: minimize risks of HTTP Desync attacks

http-desync-guardian

Analyze HTTP requests to minimize risks of HTTP Desync attacks (precursor for HTTP request smuggling/splitting).

Overview

HTTP/1.1 went through a long evolution since 1991 to 2014:

• HTTP/0.9 – 1991
• HTTP/1.0 – 1996
• HTTP/1.1
  • RFC 2068 – 1997
  • RFC 2616 – 1999
  • RFC 7230 – 2014

This means there is a variety of servers and clients, which might have different views on request boundaries, creating opportunities for desynchronization attacks (a.k.a. HTTP Desync).

It might seem simple to follow the latest RFC recommendations. However, for large-scale systems that have been there for a while, it may come with an unacceptable availability impact.

http_desync_guardian library is designed to analyze HTTP requests to prevent HTTP Desync attacks, balancing security and availability. It classifies requests into different categories and provides recommendations on how each tier should be handled.

It can be used either for raw HTTP request headers or already parsed by an HTTP engine. Consumers may configure logging and metrics collection. Logging is rate limited and all user data is obfuscated.

If you think you might have found a security-impacting issue, please follow our Security Notification Process.

Priorities

• Uniformity across services is key. This means request classification, logging, and metrics must happen under the hood and with minimally available settings (e.g., such as log file destination).
• Focus on reviewability. The test suite must require no knowledge about the library/programming languages but only about HTTP protocol. So it’s easy to review, contribute, and re-use.
• Security is efficient when it’s easy for users. Our goal is to make the integration of the library as simple as possible.
• Ultralight. The overhead must be minimal and impose no tangible tax on request handling (see benchmarks).

Supported HTTP versions

The main focus of this library is HTTP/1.1. See tests for all covered cases. Predecessors of HTTP/1.1 don’t support connection re-use which limits opportunities for HTTP Desync, however some proxies may upgrade such requests to HTTP/1.1 and re-use backend connections, which may allow to craft malicious HTTP/1.0 requests. That’s why they are analyzed using the same criteria as HTTP/1.1. For other protocol versions have the following exceptions:

• HTTP/0.9 requests are never considered Compliant, but are classified as Acceptable. If any of Content-Length/Transfer-Encoding is present then it’s Ambiguous.
• HTTP/1.0 – the presence of Transfer-Encoding makes a request Ambiguous.
• HTTP/2+ is out of scope. But if your proxy downgrades HTTP/2 to HTTP/1.1, make sure the outgoing request is analyzed.

Install & Use