{"id":"EEF-CVE-2026-82726","summary":"AshPhoenix get_subdomain maps a crafted or differently-cased Host header to an arbitrary tenant","details":"## Summary\n\nPermissive Regular Expression vulnerability in ash-project ash_phoenix lets a remote client select the tenant an Ash application uses, or degrade the request, by sending a crafted `Host` header.\n\n`AshPhoenix.Helpers.get_subdomain/2` stripped the root domain with `String.replace(host, ~r/.?#{root_host}/, \"\")`. The root host was interpolated raw, so each `.` became a wildcard and any metacharacter a pattern, and the replace was global and unanchored, so a match was removed from anywhere in the string. With `root_host` `example.com`, `Host: foo.exampleXcom.attacker.net` returned the tenant `foo.attacker.net`. A metacharacter-bearing or `nil` root host degraded the pattern or raised on every request. The comparison was also case-sensitive, so `TENANT.EXAMPLE.COM` and `EXAMPLE.COM` slipped past the root-host allowlist. `conn.host` comes from the client `Host` header. The fix matches the root host case-insensitively and only as an exact trailing suffix.\n\nThis issue affects ash_phoenix: from 2.1.26 before 2.3.25.\n\n## Configurations\n\nThe application uses subdomain-based multitenancy via `AshPhoenix.Helpers.get_subdomain/2` (for example through `AshPhoenix.LiveView.SubdomainHook`) to select the tenant from the request host.","aliases":["CVE-2026-82726","GHSA-rpf8-q9jh-qxrr"],"modified":"2026-09-08T03:30:04.063153617Z","published":"2026-08-31T03:05:38.612Z","database_specific":{"cpe_ids":["cpe:2.3:a:ash-project:ash_phoenix:*:*:*:*:*:*:*:*"],"cwe_ids":["CWE-625","CWE-178"],"capec_ids":["CAPEC-153"]},"references":[{"type":"ADVISORY","url":"https://github.com/ash-project/ash_phoenix/security/advisories/GHSA-rpf8-q9jh-qxrr"},{"type":"WEB","url":"https://cna.erlef.org/cves/CVE-2026-82726.html"},{"type":"FIX","url":"https://github.com/ash-project/ash_phoenix/commit/8306f29e77526840c89f3cd244996ce7c0fa2cda"},{"type":"PACKAGE","url":"https://hex.pm/packages/ash_phoenix"}],"affected":[{"package":{"name":"ash_phoenix","ecosystem":"Hex","purl":"pkg:hex/ash_phoenix"},"ranges":[{"type":"SEMVER","events":[{"introduced":"2.1.26"},{"fixed":"2.3.25"}]}],"versions":["2.1.26","2.2.0","2.3.0","2.3.1","2.3.10","2.3.11","2.3.12","2.3.13","2.3.14","2.3.15","2.3.16","2.3.17","2.3.18","2.3.19","2.3.2","2.3.20","2.3.21","2.3.22","2.3.23","2.3.24","2.3.3","2.3.4","2.3.5","2.3.6","2.3.7","2.3.8","2.3.9"],"database_specific":{"source":"https://cna.erlef.org/osv/EEF-CVE-2026-82726.json"}},{"ranges":[{"type":"GIT","repo":"https://github.com/ash-project/ash_phoenix","events":[{"introduced":"9a5ea4d377bc263de321d79574872a3dfc4fb541"},{"fixed":"8306f29e77526840c89f3cd244996ce7c0fa2cda"}]}],"versions":["v2.3.24","v2.3.23","v2.3.22","v2.3.21","v2.3.20","v2.3.19","v2.3.18","v2.3.17","v2.3.10","v2.3.16","v2.3.15","v2.3.14","v2.3.13","v2.3.12","v2.3.11","v2.3.9","v2.3.8","v2.3.7","v2.3.6","v2.3.5","v2.3.4","v2.3.3","v2.3.2","v2.3.1","v2.3.0","v2.2.0","v2.1.26"],"database_specific":{"source":"https://cna.erlef.org/osv/EEF-CVE-2026-82726.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N"}],"credits":[{"name":"Peter Ullrich","type":"FINDER"},{"name":"Peter Ullrich","type":"REPORTER"},{"name":"Zach Daniel / Ash Project","type":"REMEDIATION_DEVELOPER"},{"name":"Jonatan Männchen / EEF","type":"COORDINATOR"}]}