{"id":"CVE-2021-22903","aliases":["GHSA-5hq2-xf89-9jxq"],"url":"https://o3.security/vulnerability/CVE-2021-22903","summary":"Possible Open Redirect Vulnerability in Action Pack","details":"The actionpack ruby gem before 6.1.3.2 suffers from a possible open redirect vulnerability. Specially crafted Host headers in combination with certain \"allowed host\" formats can cause the Host Authorization middleware in Action Pack to redirect users to a malicious website. This is similar to CVE-2021-22881. Strings in config.hosts that do not have a leading dot are converted to regular expressions without proper escaping. This causes, for example, `config.hosts << \"sub.example.com\"` to permit a request with a Host header value of `sub-example.com`.","published":"2021-06-11T16:15:11.437Z","modified":"2026-08-07T15:15:08.955223Z","cvss":{"score":6.1,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N"},"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[{"ecosystem":"RubyGems","name":"actionpack","fixedVersion":"6.1.3.2"}],"fix":null,"references":[{"type":"REPORT","url":"https://hackerone.com/reports/1148025"},{"type":"FIX","url":"https://discuss.rubyonrails.org/t/cve-2021-22903-possible-open-redirect-vulnerability-in-action-pack/77867"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-07T15:15:08.955223Z"}}