{"id":"CVE-2026-82726","state":"PUBLISHED","title":"AshPhoenix get_subdomain maps a crafted or differently-cased Host header to an arbitrary tenant","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.\n\nAshPhoenix.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.","publishedAt":"2026-08-31T03:05:38.612Z","updatedAt":"2026-08-31T14:47:35.274Z","severity":{"score":6.3,"label":"Medium","version":"4.0","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","source":"EEF"},"assigner":"EEF","products":["ash-project ash_phoenix"],"affected":[{"vendor":"ash-project","product":"ash_phoenix","packageName":"ash_phoenix","packageURL":"pkg:hex/ash_phoenix","defaultStatus":"unaffected","versions":[{"version":"2.1.26","status":"affected","lessThan":"2.3.25","versionType":"semver"}],"collectionURL":"https://repo.hex.pm","cpes":["cpe:2.3:a:ash-project:ash_phoenix:*:*:*:*:*:*:*:*"],"modules":["'Elixir.AshPhoenix.Helpers'"],"programFiles":["lib/ash_phoenix/helpers.ex"],"programRoutines":[{"name":"'Elixir.AshPhoenix.Helpers':get_subdomain/2"}],"repo":"https://github.com/ash-project/ash_phoenix"},{"vendor":"ash-project","product":"ash_phoenix","packageName":"ash-project/ash_phoenix","packageURL":"pkg:github/ash-project/ash_phoenix","defaultStatus":"unaffected","versions":[{"version":"9a5ea4d377bc263de321d79574872a3dfc4fb541","status":"affected","lessThan":"8306f29e77526840c89f3cd244996ce7c0fa2cda","versionType":"git"}],"collectionURL":"https://github.com","cpes":["cpe:2.3:a:ash-project:ash_phoenix:*:*:*:*:*:*:*:*"],"modules":["'Elixir.AshPhoenix.Helpers'"],"programFiles":["lib/ash_phoenix/helpers.ex"],"programRoutines":[{"name":"'Elixir.AshPhoenix.Helpers':get_subdomain/2"}],"repo":"https://github.com/ash-project/ash_phoenix"}],"references":["https://github.com/ash-project/ash_phoenix/security/advisories/GHSA-rpf8-q9jh-qxrr","https://cna.erlef.org/cves/CVE-2026-82726.html","https://osv.dev/vulnerability/EEF-CVE-2026-82726","https://github.com/ash-project/ash_phoenix/commit/8306f29e77526840c89f3cd244996ce7c0fa2cda"],"weaknesses":["CWE-625","CWE-178"],"ingestedAt":"2026-10-29T20:13:15.269Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/82xxx/CVE-2026-82726.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-82726","state":"PUBLISHED","datePublished":"2026-08-31T03:05:38.612Z","dateUpdated":"2026-08-31T14:47:35.274Z","assignerShortName":"EEF","assignerOrgId":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","dateReserved":"2026-08-31T00:59:08.960Z"},"containers":{"cna":{"title":"AshPhoenix get_subdomain maps a crafted or differently-cased Host header to an arbitrary tenant","descriptions":[{"lang":"en","value":"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.\n\nAshPhoenix.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."}],"affected":[{"vendor":"ash-project","product":"ash_phoenix","packageName":"ash_phoenix","packageURL":"pkg:hex/ash_phoenix","defaultStatus":"unaffected","versions":[{"version":"2.1.26","status":"affected","lessThan":"2.3.25","versionType":"semver"}],"collectionURL":"https://repo.hex.pm","cpes":["cpe:2.3:a:ash-project:ash_phoenix:*:*:*:*:*:*:*:*"],"modules":["'Elixir.AshPhoenix.Helpers'"],"programFiles":["lib/ash_phoenix/helpers.ex"],"programRoutines":[{"name":"'Elixir.AshPhoenix.Helpers':get_subdomain/2"}],"repo":"https://github.com/ash-project/ash_phoenix"},{"vendor":"ash-project","product":"ash_phoenix","packageName":"ash-project/ash_phoenix","packageURL":"pkg:github/ash-project/ash_phoenix","defaultStatus":"unaffected","versions":[{"version":"9a5ea4d377bc263de321d79574872a3dfc4fb541","status":"affected","lessThan":"8306f29e77526840c89f3cd244996ce7c0fa2cda","versionType":"git"}],"collectionURL":"https://github.com","cpes":["cpe:2.3:a:ash-project:ash_phoenix:*:*:*:*:*:*:*:*"],"modules":["'Elixir.AshPhoenix.Helpers'"],"programFiles":["lib/ash_phoenix/helpers.ex"],"programRoutines":[{"name":"'Elixir.AshPhoenix.Helpers':get_subdomain/2"}],"repo":"https://github.com/ash-project/ash_phoenix"}],"references":[{"url":"https://github.com/ash-project/ash_phoenix/security/advisories/GHSA-rpf8-q9jh-qxrr","tags":["vendor-advisory","related"]},{"url":"https://cna.erlef.org/cves/CVE-2026-82726.html","tags":["related"]},{"url":"https://osv.dev/vulnerability/EEF-CVE-2026-82726","tags":["related"]},{"url":"https://github.com/ash-project/ash_phoenix/commit/8306f29e77526840c89f3cd244996ce7c0fa2cda","tags":["patch"]}],"metrics":[{"cvssV4_0":{"Automatable":"NOT_DEFINED","Recovery":"NOT_DEFINED","Safety":"NOT_DEFINED","attackComplexity":"LOW","attackRequirements":"PRESENT","attackVector":"NETWORK","baseScore":6.3,"baseSeverity":"MEDIUM","privilegesRequired":"NONE","providerUrgency":"NOT_DEFINED","subAvailabilityImpact":"NONE","subConfidentialityImpact":"NONE","subIntegrityImpact":"NONE","userInteraction":"NONE","valueDensity":"NOT_DEFINED","vectorString":"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","version":"4.0","vulnAvailabilityImpact":"LOW","vulnConfidentialityImpact":"LOW","vulnIntegrityImpact":"LOW","vulnerabilityResponseEffort":"NOT_DEFINED"},"format":"CVSS","scenarios":[{"lang":"en","value":"GENERAL"}]}],"problemTypes":[{"descriptions":[{"cweId":"CWE-625","description":"CWE-625 Permissive Regular Expression","lang":"en","type":"CWE"}]},{"descriptions":[{"cweId":"CWE-178","description":"CWE-178 Improper Handling of Case Sensitivity","lang":"en","type":"CWE"}]}],"providerMetadata":{"shortName":"EEF","orgId":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","dateUpdated":"2026-08-31T03:05:38.612Z"},"configurations":[{"lang":"en","supportingMedia":[{"base64":false,"type":"text/html","value":"<p>The application uses subdomain-based multitenancy via <code>AshPhoenix.Helpers.get_subdomain/2</code> (for example through <code>AshPhoenix.LiveView.SubdomainHook</code>) to select the tenant from the request host.</p>"},{"base64":false,"type":"text/markdown","value":"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."}],"value":"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."}],"cpeApplicability":[{"nodes":[{"cpeMatch":[{"criteria":"cpe:2.3:a:ash-project:ash_phoenix:*:*:*:*:*:*:*:*","versionEndExcluding":"2.3.25","versionStartIncluding":"2.1.26","vulnerable":true}],"negate":false,"operator":"OR"}],"operator":"AND"}],"credits":[{"lang":"en","type":"finder","value":"Peter Ullrich"},{"lang":"en","type":"reporter","value":"Peter Ullrich"},{"lang":"en","type":"remediation developer","value":"Zach Daniel / Ash Project"},{"lang":"en","type":"coordinator","value":"Jonatan Männchen / EEF"}],"impacts":[{"capecId":"CAPEC-153","descriptions":[{"lang":"en","value":"CAPEC-153 Input Data Manipulation"}]}],"source":{"discovery":"EXTERNAL"}},"adp":[{"title":"CISA ADP Vulnrichment","references":[{"url":"https://github.com/ash-project/ash_phoenix/security/advisories/GHSA-rpf8-q9jh-qxrr","tags":["exploit"]}],"metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-08-31T14:47:10.055608Z","id":"CVE-2026-82726","options":[{"Exploitation":"poc"},{"Automatable":"no"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-08-31T14:47:35.274Z"}}]}}}