CVE-2026-82726 (GCVE-0-2026-82726)
Vulnerability from cvelistv5 – Published: 2026-08-31 03:05 – Updated: 2026-08-31 14:47
VLAI
EPSS
VEX
Title
AshPhoenix get_subdomain maps a crafted or differently-cased Host header to an arbitrary tenant
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.
Severity
SSVC
Exploitation: poc
Automatable: no
Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-08-31 14:47 UTC
Assigner
References
4 references
| URL | Tags |
|---|---|
| https://github.com/ash-project/ash_phoenix/securi… | vendor-advisoryrelated |
| 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… | patch |
Impacted products
2 products
| Vendor | Product | Version | |
|---|---|---|---|
| ash-project | ash_phoenix |
Affected:
2.1.26 , < 2.3.25
(semver)
cpe:2.3:a:ash-project:ash_phoenix:*:*:*:*:*:*:*:* |
|
| ash-project | ash_phoenix |
Affected:
9a5ea4d377bc263de321d79574872a3dfc4fb541 , < 8306f29e77526840c89f3cd244996ce7c0fa2cda
(git)
cpe:2.3:a:ash-project:ash_phoenix:*:*:*:*:*:*:*:* |
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],
"packageName": "ash-project/ash_phoenix",
"packageURL": "pkg:github/ash-project/ash_phoenix",
"product": "ash_phoenix",
"programFiles": [
"lib/ash_phoenix/helpers.ex"
],
"programRoutines": [
{
"name": "\u0027Elixir.AshPhoenix.Helpers\u0027:get_subdomain/2"
}
],
"repo": "https://github.com/ash-project/ash_phoenix",
"vendor": "ash-project",
"versions": [
{
"lessThan": "8306f29e77526840c89f3cd244996ce7c0fa2cda",
"status": "affected",
"version": "9a5ea4d377bc263de321d79574872a3dfc4fb541",
"versionType": "git"
}
]
}
],
"configurations": [
{
"lang": "en",
"supportingMedia": [
{
"base64": false,
"type": "text/html",
"value": "\u003cp\u003eThe application uses subdomain-based multitenancy via \u003ccode\u003eAshPhoenix.Helpers.get_subdomain/2\u003c/code\u003e (for example through \u003ccode\u003eAshPhoenix.LiveView.SubdomainHook\u003c/code\u003e) to select the tenant from the request host.\u003c/p\u003e"
},
{
"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 M\u00e4nnchen / EEF"
}
],
"descriptions": [
{
"lang": "en",
"supportingMedia": [
{
"base64": false,
"type": "text/html",
"value": "\u003cp\u003ePermissive 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 \u003ccode\u003eHost\u003c/code\u003e header.\u003c/p\u003e\n\u003cp\u003e\u003ccode\u003eAshPhoenix.Helpers.get_subdomain/2\u003c/code\u003e stripped the root domain with \u003ccode\u003eString.replace(host, ~r/.?#{root_host}/, \"\")\u003c/code\u003e. The root host was interpolated raw, so each \u003ccode\u003e.\u003c/code\u003e 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 \u003ccode\u003eroot_host\u003c/code\u003e \u003ccode\u003eexample.com\u003c/code\u003e, \u003ccode\u003eHost: foo.exampleXcom.attacker.net\u003c/code\u003e returned the tenant \u003ccode\u003efoo.attacker.net\u003c/code\u003e. A metacharacter-bearing or \u003ccode\u003enil\u003c/code\u003e root host degraded the pattern or raised on every request. The comparison was also case-sensitive, so \u003ccode\u003eTENANT.EXAMPLE.COM\u003c/code\u003e and \u003ccode\u003eEXAMPLE.COM\u003c/code\u003e slipped past the root-host allowlist. \u003ccode\u003econn.host\u003c/code\u003e comes from the client \u003ccode\u003eHost\u003c/code\u003e header. The fix matches the root host case-insensitively and only as an exact trailing suffix.\u003c/p\u003e\n\u003cp\u003eThis issue affects ash_phoenix: from 2.1.26 before 2.3.25.\u003c/p\u003e"
},
{
"base64": false,
"type": "text/markdown",
"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\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."
}
],
"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."
}
],
"impacts": [
{
"capecId": "CAPEC-153",
"descriptions": [
{
"lang": "en",
"value": "CAPEC-153 Input Data Manipulation"
}
]
}
],
"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": {
"dateUpdated": "2026-08-31T03:05:38.612Z",
"orgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"shortName": "EEF"
},
"references": [
{
"tags": [
"vendor-advisory",
"related"
],
"url": "https://github.com/ash-project/ash_phoenix/security/advisories/GHSA-rpf8-q9jh-qxrr"
},
{
"tags": [
"related"
],
"url": "https://cna.erlef.org/cves/CVE-2026-82726.html"
},
{
"tags": [
"related"
],
"url": "https://osv.dev/vulnerability/EEF-CVE-2026-82726"
},
{
"tags": [
"patch"
],
"url": "https://github.com/ash-project/ash_phoenix/commit/8306f29e77526840c89f3cd244996ce7c0fa2cda"
}
],
"source": {
"discovery": "EXTERNAL"
},
"title": "AshPhoenix get_subdomain maps a crafted or differently-cased Host header to an arbitrary tenant"
}
},
"cveMetadata": {
"assignerOrgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"assignerShortName": "EEF",
"cveId": "CVE-2026-82726",
"datePublished": "2026-08-31T03:05:38.612Z",
"dateReserved": "2026-08-31T00:59:08.960Z",
"dateUpdated": "2026-08-31T14:47:35.274Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2"
}
}
}
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Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
model, served locally by ML-Gateway.
They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
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Related by attack behaviour
Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.
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