AshPhoenix get_subdomain maps a crafted or differently-cased Host header to an arbitrary tenant (CVE-2026-82726) | HOL Guard CVE

Unknown severity · Source severity not reportedCVE-2026-82726

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

Answer in brief

CVE-2026-82726 records a Unknown severity vulnerability in AshPhoenix get_subdomain maps a crafted or differently-cased Host header to an arbitrary tenant. The current sources do not mark it as known exploited. The current feed maps ash-project/ash_phoenix (generic), ash-project/ash_phoenix (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Aug 31, 2026Updated Aug 31, 2026Source checked Aug 31, 2026First seen by HOL Aug 31, 2026Material review Aug 31, 2026

Upstream Advisory

Key facts

Risk: Unknown severitySource severity not reported
Exploitation: Not marked as known exploited
Affected software: 2 mapped packages or products
Fix availability: Available

Why this deserves its current priority

A CVSS score is not reported in the current record. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps ash-project/ash_phoenix (generic), ash-project/ash_phoenix (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
ash-project/ash_phoenixgeneric	>=2.1.26 <2.3.25	2.3.25
ash-project/ash_phoenixgeneric	>=9a5ea4d377bc263de321d79574872a3dfc4fb541 <8306f29e77526840c89f3cd244996ce7c0fa2cda	8306f29e77526840c89f3cd244996ce7c0fa2cda

Recommended response

Check inventory. Check lockfiles and deployed manifests for ash-project/ash_phoenix, ash-project/ash_phoenix.
Review the reported fix. Update ash-project/ash_phoenix to 2.3.25; ash-project/ash_phoenix to 8306f29e77526840c89f3cd244996ce7c0fa2cda if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Aug 31, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Aug 31, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Aug 31, 2026

Sources and claim methodology

Upstream source 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.

Quoted source text, attributed separately from HOL analysis.