In the CGI gem before 0.4.2 for Ruby, a Regular Expression Denial of Service (ReDoS) vulnerability exists in the Util#escapeElement method.

cgi.rb in Ruby through 2.6.x, through 3.0x, and through 3.1.x allows HTTP header injection. If a CGI application using the CGI library inserts untrusted input into the HTTP response header, an attacker can exploit it to insert a newline character to split a header, and inject malicious content to deceive clients.

References: https://www.ruby-lang.org/en/security/ https://www.ruby-lang.org/en/news/2022/11/22/http-response-splitting-in-cgi-cve-2021-33621/ https://github.com/rubysec/ruby-advisory-db/blob/master/gems/cgi/CVE-2021-33621.yml https://github.com/ruby/cgi/compare/v0.1.0.1...v0.1.0.2