Sinatra is vulnerable to ReDoS through ETag header value generation

Summary

There is a denial of service vulnerability in the If-Match and If-None-Match header parsing component of Sinatra, if the etag method is used when constructing the response and you are using Ruby < 3.2.

Details

Carefully crafted input can cause If-Match and If-None-Match header parsing in Sinatra to take an unexpected amount of time, possibly resulting in a denial of service attack vector. This header is typically involved in generating the ETag header value. Any applications that use the etag method when generating a response are impacted if they are using Ruby below version 3.2.

Resources

• https://github.com/sinatra/sinatra/issues/2120 (report)
• https://github.com/sinatra/sinatra/pull/2121 (fix)
• https://github.com/sinatra/sinatra/pull/1823 (older ReDoS vulnerability)
• https://bugs.ruby-lang.org/issues/19104 (fix in Ruby >= 3.2)