"In Puma (RubyGem) before 4.3.3 and 3.12.4, if an application using Puma allows untrusted input in an early-hints header, an attacker can use a carriage return character 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-2020-5247, which fixed this vulnerability but only for regular responses. This has been fixed in 4.3.3 and 3.12.4."
This has been fixed by maintainer:
Fixed version: https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=cc4baf2d7281a98d9016e598b7784766da4529ea
Removing some old (also for bug 711076): https://gitweb.gentoo.org/repo/gentoo.git/commit/www-servers/puma?id=78d16ec499eaaf69025d7ce840b2ce3c68bba140
Changing to [glsa?]
GLSA Vote: No!
Repository is clean, all done!