Sinatra Denial-of-Service Vulnerability in ETag Header Parsing

A denial-of-service vulnerability has been identified in Sinatra versions prior to 4.2.0. The issue arises in the parsing of 'If-Match' and 'If-None-Match' headers when the 'etag' method is used to construct responses. This vulnerability can cause the header parsing to take an excessive amount of time, potentially leading to a denial-of-service condition. Applications that utilize the 'etag' method in response generation are affected, particularly those running on Ruby versions prior to 3.2.

Impact

Exploitation of this vulnerability can lead to a denial-of-service condition, causing applications to become unresponsive or slow.

Reproduction

The vulnerability can be reproduced by sending a request with carefully crafted 'If-Match' or 'If-None-Match' headers to a Sinatra application that uses the 'etag' method in its response. This can be done using a tool like curl or Postman, or by writing a custom script that sends the appropriate headers. The application will then take an unexpectedly long time to process the request, demonstrating the denial-of-service condition.

Remediation

Users can upgrade to Sinatra version 4.2.0 or later to address this vulnerability. Additionally, applications running on Ruby 3.2 or later are not affected.