Vulnerability advisory
EEF-CVE-2026-82726
AshPhoenix get_subdomain maps a crafted or differently-cased Host header to an arbitrary tenant
Also known as CVE-2026-82726GHSA-rpf8-q9jh-qxrr
- CVSS 4.0
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
Affected versions
| Affected | Fixed in |
|---|---|
2.1.26 to before 2.3.25 | 2.3.25Advisories → |
Repository
| Affected commits | Fixed by commit |
|---|---|
| GIT github.com/ash-project/ash_phoenix ↗ | |
| 9a5ea4d377bc263de321d79574872a3dfc4fb541 to before 8306f29e77526840c89f3cd244996ce7c0fa2cda | 8306f29e77526840c89f3cd244996ce7c0fa2cda |
Also listed as affected (27)
| |
Description
Summary
Permissive 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.
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.
This issue affects ash_phoenix: from 2.1.26 before 2.3.25.
Configurations
The 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.