Vulnerability · Published Aug 31, 2026 · Assigned by EEF

CVE-2026-82726AshPhoenix get_subdomain maps a crafted or differently-cased Host header to an arbitrary tenant

Medium 6.3

In plain English

A medium-severity security flaw in ash_phoenix from ash-project. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 45% of all known vulnerabilities).

Severity (CVSS 4.0)6.3Medium

Exploit odds (30 days)0.5%top 55.4% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

Official description

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.

Affected products (as reported)

Vendor	Product	Versions
ash-project	ash_phoenix	2.1.26 – before 2.3.25
ash-project	ash_phoenix	9a5ea4d377bc263de321d79574872a3dfc4fb541 – before 8306f29e77526840c89f3cd244996ce7c0fa2cda

Weakness: CWE-625, CWE-178 · Vector: 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

References

https://github.com/ash-project/ash_phoenix/security/advisories/GHSA-rpf8-q9jh-qxrr vendor-advisory, related
https://cna.erlef.org/cves/CVE-2026-82726.html related
https://osv.dev/vulnerability/EEF-CVE-2026-82726 related
https://github.com/ash-project/ash_phoenix/commit/8306f29e77526840c89f3cd244996ce7c0fa2cda patch