{"id":"CVE-2021-21291","aliases":["BIT-oauth2-proxy-2021-21291","EUVD-2021-0944","GHSA-4mf2-f3wh-gvf2","GO-2022-0790"],"status":"published","title":"Subdomain checking of whitelisted domains could allow unintended redirects","description":"OAuth2 Proxy is an open-source reverse proxy and static file server that provides authentication using Providers (Google, GitHub, and others) to validate accounts by email, domain or group. In OAuth2 Proxy before version 7.0.0, for users that use the whitelist domain feature, a domain that ended in a similar way to the intended domain could have been allowed as a redirect. For example, if a whitelist domain was configured for \".example.com\", the intention is that subdomains of example.com are allowed. Instead, \"example.com\" and \"badexample.com\" could also match. This is fixed in version 7.0.0 onwards. As a workaround, one can disable the whitelist domain feature and run separate OAuth2 Proxy instances for each subdomain.","severity":{"version":"3.1","score":4.7,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:L/A:N","level":"medium","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-11","score":0.01595,"percentile":0.76052,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-601"],"published":"2021-02-02T19:05:18Z","modified":"2026-10-24T10:50:40Z","fixes":[{"ecosystem":"Go","package":"github.com/oauth2-proxy/oauth2-proxy/v7","fixed_in":["7.0.0"],"sources":["ghsa","osv"]},{"ecosystem":"Bitnami","package":"oauth2-proxy","fixed_in":["7.0.0"],"sources":["osv"]}],"affected":[{"source":"ghsa","ecosystem":"Go","package":"github.com/oauth2-proxy/oauth2-proxy/v7","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"7.0.0"}]}]},{"source":"ghsa","ecosystem":"Go","package":"github.com/oauth2-proxy/oauth2-proxy","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"last_affected":"3.2.0"}]}]},{"source":"osv","ecosystem":"Bitnami","package":"oauth2-proxy","ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"7.0.0"}]}]},{"source":"osv","ecosystem":"Go","package":"github.com/oauth2-proxy/oauth2-proxy/v7","ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"7.0.0"}]}]},{"source":"osv","ecosystem":"Go","package":"github.com/oauth2-proxy/oauth2-proxy","ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"last_affected":"3.2.0"}]}]},{"source":"osv","ecosystem":"Go","package":"github.com/oauth2-proxy/oauth2-proxy","ranges":[{"type":"SEMVER","events":[{"introduced":"0"}]}]},{"source":"osv","ecosystem":"Go","package":"github.com/oauth2-proxy/oauth2-proxy/v7","ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"7.0.0"}]}]}],"products":[{"vendor":"oauth2-proxy","product":"oauth2-proxy"},{"vendor":"oauth2_proxy_project","product":"oauth2_proxy"}],"references":[{"url":"https://github.com/oauth2-proxy/oauth2-proxy/security/advisories/GHSA-4mf2-f3wh-gvf2","tags":["x_refsource_CONFIRM","x_transferred","Exploit","Third Party Advisory","advisory","evidence","web"]},{"url":"https://github.com/oauth2-proxy/oauth2-proxy/releases/tag/v7.0.0","tags":["x_refsource_MISC","x_transferred","Release Notes","Third Party Advisory","advisory","web"]},{"url":"https://pkg.go.dev/github.com/oauth2-proxy/oauth2-proxy/v7","tags":["x_refsource_MISC","x_transferred","Product","Third Party Advisory","advisory","web"]},{"url":"https://github.com/oauth2-proxy/oauth2-proxy/commit/780ae4f3c99b579cb2ea9845121caebb6192f725","tags":["x_refsource_MISC","x_transferred","Patch","Third Party Advisory","advisory","fix","web"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2021-21291","tags":["web","advisory"]},{"url":"https://github.com/advisories/GHSA-4mf2-f3wh-gvf2"}],"sources":{"cve":[{"id":"CVE-2021-21291","title":"Subdomain checking of whitelisted domains could allow unintended redirects","description":"OAuth2 Proxy is an open-source reverse proxy and static file server that provides authentication using Providers (Google, GitHub, and others) to validate accounts by email, domain or group. In OAuth2 Proxy before version 7.0.0, for users that use the whitelist domain feature, a domain that ended in a similar way to the intended domain could have been allowed as a redirect. For example, if a whitelist domain was configured for \".example.com\", the intention is that subdomains of example.com are allowed. Instead, \"example.com\" and \"badexample.com\" could also match. This is fixed in version 7.0.0 onwards. As a workaround, one can disable the whitelist domain feature and run separate OAuth2 Proxy instances for each subdomain.","status":"published","published":"2021-02-02T19:05:18Z","modified":"2024-08-03T18:09:15.152Z","cvss":[{"version":"3.1","score":4.7,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:L/A:N","level":"medium","assessor":"cna"}],"cwes":["CWE-601"],"updated_at":"2026-11-02T14:33:00.137099Z"}],"euvd":[{"id":"EUVD-2021-0944","description":"OAuth2 Proxy is an open-source reverse proxy and static file server that provides authentication using Providers (Google, GitHub, and others) to validate accounts by email, domain or group. In OAuth2 Proxy before version 7.0.0, for users that use the whitelist domain feature, a domain that ended in a similar way to the intended domain could have been allowed as a redirect. For example, if a whitelist domain was configured for \".example.com\", the intention is that subdomains of example.com are allowed. Instead, \"example.com\" and \"badexample.com\" could also match. This is fixed in version 7.0.0 onwards. As a workaround, one can disable the whitelist domain feature and run separate OAuth2 Proxy instances for each subdomain.","status":"published","published":"2021-02-02T19:05:18Z","modified":"2024-08-03T18:09:15Z","cvss":[{"version":"3.1","score":4.7,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:L/A:N","level":"medium"}],"updated_at":"2026-11-03T03:25:06.913643Z"}],"ghsa":[{"id":"GHSA-4mf2-f3wh-gvf2","title":"Subdomain checking of whitelisted domains could allow unintended redirects in oauth2-proxy","description":"### Impact\n_What kind of vulnerability is it? Who is impacted?_\nFor users that use the whitelist domain feature, a domain that ended in a similar way to the intended domain could have been allowed as a redirect.\n\nFor example, if a whitelist domain was configured for `.example.com`, the intention is that subdomains of `example.com` are allowed.\nInstead, `example.com` and `badexample.com` could also match.\n\n### Patches\n_Has the problem been patched? What versions should users upgrade to?_\nThis is fixed in version 7.0.0 onwards.\n\n### Workarounds\n_Is there a way for users to fix or remediate the vulnerability without upgrading?_\nDisable the whitelist domain feature and run separate OAuth2 Proxy instances for each subdomain.\n\n# Original Issue Posted by @semoac:\n\nWhitelist Domain feature is not working as expected because is not matching a dot to ensure the redirect is a subdomain.\n\n## Expected Behavior\n\nIf whitelist domain is set to `.example.com` , then `hack.alienexample.com`  should be rejected as a valid redirect.\n\n## Current Behavior\n\nThe code is removing the `dot`  from `.example.com`  and  only checking if the redirect string end with `example.com`\n\n## Possible Solution\nHere\nhttps://github.com/oauth2-proxy/oauth2-proxy/blob/c377466411f2aee180a732187edb638f2f7e57fb/oauthproxy.go#L661\n\nInclude the dot when checking the string:\n```\nstrings.HasSuffix(redirectHostname, \".\" + domainHostname)\n```\n\n## Steps to Reproduce (for bugs)\n\n```\npackage main\n\nimport (\n\t\"fmt\"\n\t\"strings\"\n)\n\nfunc validOptionalPort(port string) bool {\n\tif port == \"\" || port == \":*\" {\n\t\treturn true\n\t}\n\tif port[0] != ':' {\n\t\treturn false\n\t}\n\tfor _, b := range port[1:] {\n\t\tif b \u003c '0' || b \u003e '9' {\n\t\t\treturn false\n\t\t}\n\t}\n\treturn true\n}\n\nfunc splitHostPort(hostport string) (host, port string) {\n\thost = hostport\n\n\tcolon := strings.LastIndexByte(host, ':')\n\tif colon != -1 \u0026\u0026 validOptionalPort(host[colon:]) {\n\t\thost, port = host[:colon], host[colon+1:]\n\t}\n\n\tif strings.HasPrefix(host, \"[\") \u0026\u0026 strings.HasSuffix(host, \"]\") {\n\t\thost = host[1 : len(host)-1]\n\t}\n\n\treturn\n}\n\nfunc main() {\n\tdomain := \".example.com\"\n\tdomainHostname, _ := splitHostPort(strings.TrimLeft(domain, \".\"))\n\tredirectHostname := \"https://hack.alienexample.com\"\n\tif (strings.HasPrefix(domain, \".\") \u0026\u0026 strings.HasSuffix(redirectHostname, domainHostname)) { fmt.Println(\"This should not have happen.\")}\n}\n\n```\n\nUsers of `github.com/oauth2-proxy/oauth2-proxy` are advised to update to `github.com/oauth2-proxy/oauth2-proxy/v7`","status":"published","published":"2021-05-25T18:42:20Z","modified":"2023-01-09T05:04:49Z","cvss":[{"version":"3.1","score":5.4,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N","level":"medium"}],"cwes":["CWE-601"],"updated_at":"2026-11-02T14:36:10.502376Z"}],"nvd":[{"id":"CVE-2021-21291","description":"OAuth2 Proxy is an open-source reverse proxy and static file server that provides authentication using Providers (Google, GitHub, and others) to validate accounts by email, domain or group. In OAuth2 Proxy before version 7.0.0, for users that use the whitelist domain feature, a domain that ended in a similar way to the intended domain could have been allowed as a redirect. For example, if a whitelist domain was configured for \".example.com\", the intention is that subdomains of example.com are allowed. Instead, \"example.com\" and \"badexample.com\" could also match. This is fixed in version 7.0.0 onwards. As a workaround, one can disable the whitelist domain feature and run separate OAuth2 Proxy instances for each subdomain.","status":"published","published":"2021-02-02T19:15:14.33Z","modified":"2026-06-17T03:35:12.84Z","cvss":[{"version":"3.1","score":4.7,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:L/A:N","level":"medium","assessor":"secondary"},{"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":"2026-11-02T14:06:49.660551Z"}],"osv":[{"id":"CVE-2021-21291","description":"OAuth2 Proxy is an open-source reverse proxy and static file server that provides authentication using Providers (Google, GitHub, and others) to validate accounts by email, domain or group. In OAuth2 Proxy before version 7.0.0, for users that use the whitelist domain feature, a domain that ended in a similar way to the intended domain could have been allowed as a redirect. For example, if a whitelist domain was configured for \".example.com\", the intention is that subdomains of example.com are allowed. Instead, \"example.com\" and \"badexample.com\" could also match. This is fixed in version 7.0.0 onwards. As a workaround, one can disable the whitelist domain feature and run separate OAuth2 Proxy instances for each subdomain.","status":"published","published":"2021-02-02T19:15:14.33Z","modified":"2026-10-24T10:50:40.428991441Z","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":"2026-11-02T15:44:18.004149Z"},{"id":"GHSA-4mf2-f3wh-gvf2","title":"Subdomain checking of whitelisted domains could allow unintended redirects in oauth2-proxy","description":"### Impact\n_What kind of vulnerability is it? Who is impacted?_\nFor users that use the whitelist domain feature, a domain that ended in a similar way to the intended domain could have been allowed as a redirect.\n\nFor example, if a whitelist domain was configured for `.example.com`, the intention is that subdomains of `example.com` are allowed.\nInstead, `example.com` and `badexample.com` could also match.\n\n### Patches\n_Has the problem been patched? What versions should users upgrade to?_\nThis is fixed in version 7.0.0 onwards.\n\n### Workarounds\n_Is there a way for users to fix or remediate the vulnerability without upgrading?_\nDisable the whitelist domain feature and run separate OAuth2 Proxy instances for each subdomain.\n\n# Original Issue Posted by @semoac:\n\nWhitelist Domain feature is not working as expected because is not matching a dot to ensure the redirect is a subdomain.\n\n## Expected Behavior\n\nIf whitelist domain is set to `.example.com` , then `hack.alienexample.com`  should be rejected as a valid redirect.\n\n## Current Behavior\n\nThe code is removing the `dot`  from `.example.com`  and  only checking if the redirect string end with `example.com`\n\n## Possible Solution\nHere\nhttps://github.com/oauth2-proxy/oauth2-proxy/blob/c377466411f2aee180a732187edb638f2f7e57fb/oauthproxy.go#L661\n\nInclude the dot when checking the string:\n```\nstrings.HasSuffix(redirectHostname, \".\" + domainHostname)\n```\n\n## Steps to Reproduce (for bugs)\n\n```\npackage main\n\nimport (\n\t\"fmt\"\n\t\"strings\"\n)\n\nfunc validOptionalPort(port string) bool {\n\tif port == \"\" || port == \":*\" {\n\t\treturn true\n\t}\n\tif port[0] != ':' {\n\t\treturn false\n\t}\n\tfor _, b := range port[1:] {\n\t\tif b \u003c '0' || b \u003e '9' {\n\t\t\treturn false\n\t\t}\n\t}\n\treturn true\n}\n\nfunc splitHostPort(hostport string) (host, port string) {\n\thost = hostport\n\n\tcolon := strings.LastIndexByte(host, ':')\n\tif colon != -1 \u0026\u0026 validOptionalPort(host[colon:]) {\n\t\thost, port = host[:colon], host[colon+1:]\n\t}\n\n\tif strings.HasPrefix(host, \"[\") \u0026\u0026 strings.HasSuffix(host, \"]\") {\n\t\thost = host[1 : len(host)-1]\n\t}\n\n\treturn\n}\n\nfunc main() {\n\tdomain := \".example.com\"\n\tdomainHostname, _ := splitHostPort(strings.TrimLeft(domain, \".\"))\n\tredirectHostname := \"https://hack.alienexample.com\"\n\tif (strings.HasPrefix(domain, \".\") \u0026\u0026 strings.HasSuffix(redirectHostname, domainHostname)) { fmt.Println(\"This should not have happen.\")}\n}\n\n```\n\nUsers of `github.com/oauth2-proxy/oauth2-proxy` are advised to update to `github.com/oauth2-proxy/oauth2-proxy/v7`","status":"published","published":"2021-05-25T18:42:20Z","modified":"2026-09-10T03:49:04.327848096Z","cvss":[{"version":"3.1","score":5.4,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N","level":"medium"}],"cwes":["CWE-601"],"updated_at":"2026-11-02T15:46:37.148947Z"},{"id":"BIT-oauth2-proxy-2021-21291","title":"Subdomain checking of whitelisted domains could allow unintended redirects","description":"OAuth2 Proxy is an open-source reverse proxy and static file server that provides authentication using Providers (Google, GitHub, and others) to validate accounts by email, domain or group. In OAuth2 Proxy before version 7.0.0, for users that use the whitelist domain feature, a domain that ended in a similar way to the intended domain could have been allowed as a redirect. For example, if a whitelist domain was configured for \".example.com\", the intention is that subdomains of example.com are allowed. Instead, \"example.com\" and \"badexample.com\" could also match. This is fixed in version 7.0.0 onwards. As a workaround, one can disable the whitelist domain feature and run separate OAuth2 Proxy instances for each subdomain.","status":"published","published":"2024-03-06T10:59:20.233Z","modified":"2026-09-08T08:48:10.807835014Z","updated_at":"2026-11-02T15:28:34.343258Z"},{"id":"GO-2022-0790","title":"Subdomain checking of whitelisted domains could allow unintended redirects in oauth2-proxy in github.com/oauth2-proxy/oauth2-proxy","description":"Subdomain checking of whitelisted domains could allow unintended redirects in oauth2-proxy in github.com/oauth2-proxy/oauth2-proxy","status":"published","published":"2024-08-21T15:28:59Z","modified":"2026-03-03T04:50:53.714629Z","updated_at":"2026-11-02T15:47:00.918515Z"}]}}