Sinatra is a domain-specific language for creating web applications in Ruby. In versions prior to 4.2.0, 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. 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. Version 4.2.0 fixes the issue.

Sinatra is a domain-specific language for creating web applications in Ruby. An issue was discovered in Sinatra 2.0 before 2.2.3 and 3.0 before 3.0.4. An application is vulnerable to a reflected file download (RFD) attack that sets the Content-Disposition header of a response when the filename is derived from user-supplied input. Version 2.2.3 and 3.0.4 contain patches for this issue.

Sinatra before 2.2.0 does not validate that the expanded path matches public_dir when serving static files.

Sinatra before 2.0.2 has XSS via the 400 Bad Request page that occurs upon a params parser exception.

Sinatra rack-protection versions 1.5.4 and 2.0.0.rc3 and earlier contains a timing attack vulnerability in the CSRF token checking that can result in signatures can be exposed. This attack appear to be exploitable via network connectivity to the ruby application. This vulnerability appears to have been fixed in 1.5.5 and 2.0.0.

An issue was discovered in rack-protection/lib/rack/protection/path_traversal.rb in Sinatra 2.x before 2.0.1 on Windows. Path traversal is possible via backslash characters.