In Puma (RubyGem) before 4.3.2 and 3.12.3, if an application using Puma allows untrusted input in a response header, an attacker can use newline characters (i.e. CR, LF or/r, /n) to end the header and inject malicious content, such as additional headers or an entirely new response body. This vulnerability is known as HTTP Response Splitting.

While not an attack in itself, response splitting is a vector for several other attacks, such as cross-site scripting (XSS).

This is related to CVE-2019-16254, which fixed this vulnerability for the WEBrick Ruby web server.

This has been fixed in versions 4.3.2 and 3.12.3 by checking all headers for line endings and rejecting headers with those characters.

Last updated 25 August 2025

Last updated 11 July 2025

Last updated 11 July 2025

A flaw was discovered in Ruby in the way certain functions handled strings containing NULL bytes. Specifically, the built-in methods File.fnmatch and its alias File.fnmatch? did not properly handle path patterns containing the NULL byte. A remote attacker could exploit this flaw to make a Ruby script access unexpected files and to bypass intended file system access restrictions.