{"id":"GHSA-2gff-2mmg-m73p","summary":"Action Pack: Possible IP spoofing in Action Dispatch RemoteIp","details":"### Impact\nSince Rails 8.1.0, `ActionDispatch::RemoteIp` derives `request.remote_ip` from `Rack::Request#forwarded_for`, which under Rack 3 reads the RFC 7239 `Forwarded` header in preference to `X-Forwarded-For`. When a reverse proxy appends the client address to `X-Forwarded-For` but passes a client-supplied `Forwarded` header through unchanged, `request.remote_ip` returns an address chosen by the client, and the IP spoofing check does not raise, because it compares only `Client-Ip` with the forwarded addresses. An unauthenticated attacker could therefore spoof `request.remote_ip`, possibly bypassing IP-based access controls and rate limits keyed on the client address (including the default `by:` of `rate_limit`), and falsifying the client address in logs.\n\n### Details\nThe 8.1.0 change ([2d084af8](https://github.com/rails/rails/commit/2d084af8444a7b6b868c7cbb256172007871e78d)) switched `ActionDispatch::RemoteIp` from reading `X-Forwarded-For` directly to Rack's `forwarded_for`, in order to reuse Rack's port handling. Rails continues to honor `Forwarded`, the standard header.\n\nIn the fixed releases, when `config.action_dispatch.ip_spoofing_check` is enabled (the default), `ActionDispatch::RemoteIp` also compares the first untrusted client address in `Forwarded` with the first untrusted client address in `X-Forwarded-For`, as exact strings, and raises `ActionDispatch::RemoteIp::IpSpoofAttackError` when both headers are present and the addresses differ. Deployments whose proxies report the client address inconsistently between the two headers will receive this error after upgrading. See the `actionpack` CHANGELOG.\n\n### Affected applications\nAn application is affected if it meets all of these requirements:\n- Runs Rails 8.1.0 through 8.1.4 with Rack 3. Under Rack 2.2, `forwarded_for` reads only `X-Forwarded-For`.\n- Is served behind a proxy that does not remove or overwrite a client-supplied `Forwarded` header.\n- Relies on `request.remote_ip` for access control, rate limiting, or auditing.\n\nThe fix detects a spoofed `Forwarded` header only when the proxy also sets `X-Forwarded-For`. An application whose proxy passes a client-supplied `Forwarded` header through and sets no `X-Forwarded-For` remains exposed after upgrading, and should configure the proxy to remove or overwrite `Forwarded`, or apply the workaround below.\n\n### Mitigation\n- Upgrade to a fixed version of `actionpack`.\n- Configure reverse proxies to remove or overwrite any client-supplied `Forwarded` header.\n\n### Workarounds\nApplications whose proxies set `X-Forwarded-For` can make Rack ignore the `Forwarded` header, restoring the client address resolution of Rails 8.0, by setting `Rack::Request.forwarded_priority = [:x_forwarded]` in an initializer. This setting is available in Rack 3.0.0 and later, and it also causes Rack to ignore `Forwarded` when determining the request scheme, host, and port.\n\n### Releases\nThe fixed releases are available at the normal locations.\n\nPatches for those who cannot upgrade at once:\n- 8.1: https://github.com/rails/rails/commit/2a01a5ac521184419d9a92fa2c25e102e68cd227.patch\n\n### Versions affected\n- actionpack \u003e= 8.1, \u003c 8.1.4.1\n\n### Credit\nThis issue was responsibly reported by HackerOne researcher [luryus](https://hackerone.com/luryus).","aliases":["CVE-2026-126083"],"modified":"2026-11-10T21:30:04.269070700Z","published":"2026-11-10T21:20:06Z","database_specific":{"github_reviewed_at":"2026-11-10T21:20:06Z","nvd_published_at":null,"cwe_ids":["CWE-348"],"severity":"HIGH","github_reviewed":true},"references":[{"type":"WEB","url":"https://github.com/rails/rails/security/advisories/GHSA-2gff-2mmg-m73p"},{"type":"WEB","url":"https://github.com/rails/rails/commit/2a01a5ac521184419d9a92fa2c25e102e68cd227"},{"type":"PACKAGE","url":"https://github.com/rails/rails"},{"type":"WEB","url":"https://github.com/rails/rails/releases/tag/v8.1.4.1"},{"type":"WEB","url":"https://github.com/rubysec/ruby-advisory-db/blob/master/gems/actionpack/GHSA-2gff-2mmg-m73p.yml"}],"affected":[{"package":{"name":"actionpack","ecosystem":"RubyGems","purl":"pkg:gem/actionpack"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"8.1.0.beta1"},{"fixed":"8.1.4.1"}]}],"versions":["8.1.0","8.1.0.beta1","8.1.0.rc1","8.1.1","8.1.2","8.1.2.1","8.1.3","8.1.3.1","8.1.4"],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/11/GHSA-2gff-2mmg-m73p/GHSA-2gff-2mmg-m73p.json"}}],"schema_version":"1.9.2","severity":[{"type":"CVSS_V3","score":"CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N"}]}