Added CVE-2021-33621 for the cgi gem.

* https://www.ruby-lang.org/en/news/2022/11/22/http-response-splitting-in-cgi-cve-2021-33621/

Author: postmodern

gems/cgi/CVE-2021-33621.yml

@@ -0,0 +1,19 @@
+---
+gem: cgi
+cve: 2021-33621
+ghsa: vc47-6rqg-c7f5
+url: https://www.ruby-lang.org/en/news/2022/11/22/http-response-splitting-in-cgi-cve-2021-33621/
+title: HTTP response splitting in CGI
+date: 2022-11-18
+description: |-
+  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.
+
+cvss_v3: 8.8
+patched_versions:
+  - "~> 0.1.0.2"
+  - "~> 0.2.2"
+  - ">= 0.3.5"