{"id":"CVE-2021-22903","aliases":["EUVD-2021-0957","GHSA-5hq2-xf89-9jxq","UBUNTU-CVE-2021-22903"],"status":"published","title":"Possible Open Redirect Vulnerability in Action Pack","description":"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 \u003c\u003c \"sub.example.com\"` to permit a request with a Host header value of `sub-example.com`.","severity":{"version":"3.1","score":6.1,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N","level":"medium","assessor":"primary","from":"nvd"},"epss":{"day":"2026-11-10","score":0.0123,"percentile":0.69172,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-601"],"published":"2021-05-05T19:48:29Z","modified":"2026-10-24T10:31:01Z","fixes":[{"ecosystem":"RubyGems","package":"actionpack","fixed_in":["6.1.3.2"],"sources":["ghsa","osv"]}],"affected":[{"source":"ghsa","ecosystem":"RubyGems","package":"actionpack","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"6.1.0.rc2"},{"fixed":"6.1.3.2"}]}]},{"source":"osv","ecosystem":"RubyGems","package":"actionpack","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"6.1.0.rc2"},{"fixed":"6.1.3.2"}]}],"versions":["6.1.0","6.1.0.rc2","6.1.1","6.1.2","6.1.2.1","6.1.3","6.1.3.1"]},{"source":"osv","ecosystem":"Ubuntu:Pro:16.04:LTS","package":"rails","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2:4.1.10-1","2:4.2.5-1","2:4.2.5.1-1","2:4.2.5.2-2","2:4.2.6-1","2:4.2.6-1ubuntu0.1~esm1","2:4.2.6-1ubuntu0.1~esm2"]},{"source":"osv","ecosystem":"Ubuntu:Pro:18.04:LTS","package":"rails","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2:4.2.9-2","2:4.2.9-4","2:4.2.10-0ubuntu4","2:4.2.10-0ubuntu4+esm1","2:4.2.10-0ubuntu4+esm2"]},{"source":"osv","ecosystem":"Ubuntu:Pro:20.04:LTS","package":"rails","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2:5.2.2.1+dfsg-1ubuntu1","2:5.2.3+dfsg-3","2:5.2.3+dfsg-3ubuntu0.1~esm1"]},{"source":"osv","ecosystem":"Ubuntu:Pro:22.04:LTS","package":"rails","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2:6.0.3.7+dfsg-2","2:6.1.4.1+dfsg-8ubuntu2","2:6.1.4.1+dfsg-8ubuntu2+esm1"]},{"source":"osv","ecosystem":"Ubuntu:24.04:LTS","package":"rails","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2:6.1.7.3+dfsg-2build1","2:6.1.7.3+dfsg-3"]},{"source":"osv","ecosystem":"Ubuntu:25.10","package":"rails","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2:6.1.7.3+dfsg-7","2:7.2.2.1+dfsg-7"]},{"source":"osv","ecosystem":"Ubuntu:26.10","package":"rails","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2:7.2.3+dfsg-2","2:7.2.3.2+dfsg-2"]},{"source":"osv","ecosystem":"Ubuntu:26.04:LTS","package":"rails","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2:7.2.2.1+dfsg-7","2:7.2.2.2+dfsg-2","2:7.2.3+dfsg-2"]}],"products":[{"vendor":"rails","product":"https://github.com/rails/rails"},{"vendor":"rubyonrails","product":"rails"}],"references":[{"url":"https://hackerone.com/reports/1148025","tags":["x_refsource_MISC","x_transferred","Permissions Required","Third Party Advisory","report","web"]},{"url":"https://discuss.rubyonrails.org/t/cve-2021-22903-possible-open-redirect-vulnerability-in-action-pack/77867","tags":["x_refsource_MISC","x_transferred","Mitigation","Patch","Vendor Advisory","fix","web"]},{"url":"https://github.com/rails/rails/releases/tag/v6.1.3.2","tags":["web"]},{"url":"https://groups.google.com/g/rubyonrails-security/c/8TxqXEtgSF0","tags":["web"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2021-22903","tags":["advisory"]},{"url":"https://github.com/rubysec/ruby-advisory-db/blob/master/gems/actionpack/CVE-2021-22903.yml","tags":["web"]},{"url":"https://github.com/advisories/GHSA-5hq2-xf89-9jxq"},{"url":"https://ubuntu.com/security/CVE-2021-22903","tags":["report"]},{"url":"https://www.cve.org/CVERecord?id=CVE-2021-22903","tags":["report"]}],"sources":{"cve":[{"id":"CVE-2021-22903","description":"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 \u003c\u003c \"sub.example.com\"` to permit a request with a Host header value of `sub-example.com`.","status":"published","published":"2021-06-11T15:49:38Z","modified":"2024-08-03T18:58:25.786Z","cwes":["CWE-601"],"updated_at":"2026-11-02T14:32:58.028461Z"}],"euvd":[{"id":"EUVD-2021-0957","description":"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 \u003c\u003c \"sub.example.com\"` to permit a request with a Host header value of `sub-example.com`.","status":"published","published":"2021-06-11T15:49:38Z","modified":"2024-08-03T18:58:25Z","updated_at":"2026-11-03T03:25:01.154097Z"}],"ghsa":[{"id":"GHSA-5hq2-xf89-9jxq","title":"Possible Open Redirect Vulnerability in Action Pack","description":"There is a possible Open Redirect Vulnerability in Action Pack.\n\nVersions Affected:  \u003e= v6.1.0.rc2\nNot affected:       \u003c v6.1.0.rc2\nFixed Versions:     6.1.3.2\n\nImpact\n------\nThis is similar to CVE-2021-22881. 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\nwebsite.\n\nSince rails/rails@9bc7ea5, 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 \u003c\u003c \"sub.example.com\" to permit a request with a Host header value of sub-example.com.\n\n\nReleases\n--------\nThe fixed releases are available at the normal locations.\n\nWorkarounds\n-----------\nThe following monkey patch put in an initializer can be used as a workaround.\n\n```ruby\nclass ActionDispatch::HostAuthorization::Permissions\n  def sanitize_string(host)\n    if host.start_with?(\".\")\n      /\\A(.+\\.)?#{Regexp.escape(host[1..-1])}\\z/i\n    else\n      /\\A#{Regexp.escape host}\\z/i\n    end\n  end\nend\n```\n\nPatches\n-------\nTo aid users who aren't able to upgrade immediately we have provided patches for the two supported release series. They are in git-am format and consist of a single changeset.\n\n* 6-1-open-redirect.patch - Patch for 6.1 series\n\nPlease note that only the 6.1.Z, 6.0.Z, and 5.2.Z series are supported at present. Users of earlier unsupported releases are advised to upgrade as soon as possible as we cannot guarantee the continued availability of security fixes for unsupported releases.\n\nCredits\n-------\n\nThanks Jonathan Hefner (https://hackerone.com/jonathanhefner) for reporting this bug!","status":"published","published":"2021-05-05T19:48:29Z","modified":"2023-08-17T05:02:22Z","cvss":[{"version":"3.1","score":6.1,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N","level":"medium"}],"cwes":["CWE-601"],"updated_at":"2026-11-02T14:37:00.074932Z"}],"nvd":[{"id":"CVE-2021-22903","description":"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 \u003c\u003c \"sub.example.com\"` to permit a request with a Host header value of `sub-example.com`.","status":"published","published":"2021-06-11T16:15:11.437Z","modified":"2026-06-17T03:37:59.6Z","cvss":[{"version":"3.1","score":6.1,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N","level":"medium","assessor":"primary"},{"version":"2.0","score":5.8,"vector":"AV:N/AC:M/Au:N/C:P/I:P/A:N","level":"medium","assessor":"primary"}],"cwes":["CWE-601"],"updated_at":"2026-11-02T14:06:54.439974Z"}],"osv":[{"id":"CVE-2021-22903","description":"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 \u003c\u003c \"sub.example.com\"` to permit a request with a Host header value of `sub-example.com`.","status":"published","published":"2021-06-11T16:15:11.437Z","modified":"2026-10-24T10:31:01.380191908Z","cvss":[{"version":"3.1","score":6.1,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N","level":"medium"}],"updated_at":"2026-11-02T15:44:18.367807Z"},{"id":"GHSA-5hq2-xf89-9jxq","title":"Possible Open Redirect Vulnerability in Action Pack","description":"There is a possible Open Redirect Vulnerability in Action Pack.\n\nVersions Affected:  \u003e= v6.1.0.rc2\nNot affected:       \u003c v6.1.0.rc2\nFixed Versions:     6.1.3.2\n\nImpact\n------\nThis is similar to CVE-2021-22881. 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\nwebsite.\n\nSince rails/rails@9bc7ea5, 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 \u003c\u003c \"sub.example.com\" to permit a request with a Host header value of sub-example.com.\n\n\nReleases\n--------\nThe fixed releases are available at the normal locations.\n\nWorkarounds\n-----------\nThe following monkey patch put in an initializer can be used as a workaround.\n\n```ruby\nclass ActionDispatch::HostAuthorization::Permissions\n  def sanitize_string(host)\n    if host.start_with?(\".\")\n      /\\A(.+\\.)?#{Regexp.escape(host[1..-1])}\\z/i\n    else\n      /\\A#{Regexp.escape host}\\z/i\n    end\n  end\nend\n```\n\nPatches\n-------\nTo aid users who aren't able to upgrade immediately we have provided patches for the two supported release series. They are in git-am format and consist of a single changeset.\n\n* 6-1-open-redirect.patch - Patch for 6.1 series\n\nPlease note that only the 6.1.Z, 6.0.Z, and 5.2.Z series are supported at present. Users of earlier unsupported releases are advised to upgrade as soon as possible as we cannot guarantee the continued availability of security fixes for unsupported releases.\n\nCredits\n-------\n\nThanks Jonathan Hefner (https://hackerone.com/jonathanhefner) for reporting this bug!","status":"published","published":"2021-05-05T19:48:29Z","modified":"2024-02-16T08:18:07.647142Z","cvss":[{"version":"3.1","score":6.1,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N","level":"medium"}],"cwes":["CWE-601"],"updated_at":"2026-11-02T15:46:38.553953Z"},{"id":"UBUNTU-CVE-2021-22903","description":"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 \u003c\u003c \"sub.example.com\"` to permit a request with a Host header value of `sub-example.com`.","status":"published","published":"2021-06-11T16:15:00Z","modified":"2026-10-17T12:56:19.34910419Z","cvss":[{"version":"3.1","score":6.1,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N","level":"medium"}],"updated_at":"2026-11-02T15:54:26.29421Z"}]}}