CVE-2026-82756 (GCVE-0-2026-82756)
Vulnerability from cvelistv5 – Published: 2026-09-07 22:30 – Updated: 2026-09-08 14:43
VLAI
EPSS
VEX
Title
ash_authentication_oauth2_server interpolates a tenant-derived value into the WWW-Authenticate challenge without escaping, allowing header parameter injection
Summary
Improper Encoding or Escaping of Output vulnerability in ash-project ash_authentication_oauth2_server allows an unauthenticated attacker to inject arbitrary authentication parameters into the WWW-Authenticate challenge header.
BearerPlug and RequireScopePlug built the Bearer resource_metadata="..." challenge by interpolating a resource_metadata URL derived from the request tenant directly into the quoted value. In a multi-tenant application that sets the Ash tenant from request-controlled data (a subdomain, the Host, a path segment, or a header), a tenant containing a " closes the quoted value and appends attacker-chosen auth-params, including a second resource_metadata URL pointing at an attacker-controlled authorization server that spec-following clients follow. Carriage returns and line feeds are rejected by Plug, so this is parameter injection within one header, not response splitting.
This issue affects ash_authentication_oauth2_server: from 0.1.3 before 0.3.1.
Severity
SSVC
Exploitation: none
Automatable: no
Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-09-08 14:43 UTC
CWE
- CWE-116 - Improper Encoding or Escaping of Output
Assigner
References
4 references
| URL | Tags |
|---|---|
| https://github.com/ash-project/ash_authentication… | vendor-advisoryrelated |
| https://cna.erlef.org/cves/CVE-2026-82756.html | related |
| https://osv.dev/vulnerability/EEF-CVE-2026-82756 | related |
| https://github.com/ash-project/ash_authentication… | patch |
Impacted products
2 products
| Vendor | Product | Version | CPE status | |
|---|---|---|---|---|
| ash-project | ash_authentication_oauth2_server |
Affected:
0.1.3 , < 0.3.1
(semver)
cpe:2.3:a:ash-project:ash_authentication_oauth2_server:*:*:*:*:*:*:*:* |
||
| ash-project | ash_authentication_oauth2_server |
Affected:
99de0a1cacb5ef667c4533278b7c81ca98c00231 , < 09f97476715da031b136eaec7b2cda2363ad8149
(git)
cpe:2.3:a:ash-project:ash_authentication_oauth2_server:*:*:*:*:*:*:*:* |
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{
"name": "\u0027Elixir.AshAuthentication.Phoenix.Oauth2Server.RequireScopePlug\u0027:call/2"
}
],
"repo": "https://github.com/ash-project/ash_authentication_oauth2_server",
"vendor": "ash-project",
"versions": [
{
"lessThan": "0.3.1",
"status": "affected",
"version": "0.1.3",
"versionType": "semver"
}
]
},
{
"collectionURL": "https://github.com",
"cpes": [
"cpe:2.3:a:ash-project:ash_authentication_oauth2_server:*:*:*:*:*:*:*:*"
],
"defaultStatus": "unaffected",
"modules": [
"\u0027Elixir.AshAuthentication.Phoenix.Oauth2Server.BearerPlug\u0027",
"\u0027Elixir.AshAuthentication.Phoenix.Oauth2Server.RequireScopePlug\u0027"
],
"packageName": "ash-project/ash_authentication_oauth2_server",
"packageURL": "pkg:github/ash-project/ash_authentication_oauth2_server",
"product": "ash_authentication_oauth2_server",
"programFiles": [
"lib/ash_authentication_phoenix/oauth2_server/bearer_plug.ex",
"lib/ash_authentication_phoenix/oauth2_server/require_scope_plug.ex"
],
"programRoutines": [
{
"name": "\u0027Elixir.AshAuthentication.Phoenix.Oauth2Server.BearerPlug\u0027:call/2"
},
{
"name": "\u0027Elixir.AshAuthentication.Phoenix.Oauth2Server.RequireScopePlug\u0027:call/2"
}
],
"repo": "https://github.com/ash-project/ash_authentication_oauth2_server",
"vendor": "ash-project",
"versions": [
{
"lessThan": "09f97476715da031b136eaec7b2cda2363ad8149",
"status": "affected",
"version": "99de0a1cacb5ef667c4533278b7c81ca98c00231",
"versionType": "git"
}
]
}
],
"configurations": [
{
"lang": "en",
"supportingMedia": [
{
"base64": false,
"type": "text/html",
"value": "\u003cp\u003eReachable only in a multi-tenant application that derives the Ash tenant from request-controlled input (subdomain, \u003ccode\u003eHost\u003c/code\u003e, path, or header) and uses \u003ccode\u003eBearerPlug\u003c/code\u003e or \u003ccode\u003eRequireScopePlug\u003c/code\u003e; the tenant reaches the challenge through the server\u0027s tenant-aware \u003ccode\u003eresource_url\u003c/code\u003e.\u003c/p\u003e"
},
{
"base64": false,
"type": "text/markdown",
"value": "Reachable only in a multi-tenant application that derives the Ash tenant from request-controlled input (subdomain, `Host`, path, or header) and uses `BearerPlug` or `RequireScopePlug`; the tenant reaches the challenge through the server\u0027s tenant-aware `resource_url`."
}
],
"value": "Reachable only in a multi-tenant application that derives the Ash tenant from request-controlled input (subdomain, Host, path, or header) and uses BearerPlug or RequireScopePlug; the tenant reaches the challenge through the server\u0027s tenant-aware resource_url."
}
],
"cpeApplicability": [
{
"nodes": [
{
"cpeMatch": [
{
"criteria": "cpe:2.3:a:ash-project:ash_authentication_oauth2_server:*:*:*:*:*:*:*:*",
"versionEndExcluding": "0.3.1",
"versionStartIncluding": "0.1.3",
"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\u003eImproper Encoding or Escaping of Output vulnerability in ash-project ash_authentication_oauth2_server allows an unauthenticated attacker to inject arbitrary authentication parameters into the \u003ccode\u003eWWW-Authenticate\u003c/code\u003e challenge header.\u003c/p\u003e\n\u003cp\u003e\u003ccode\u003eBearerPlug\u003c/code\u003e and \u003ccode\u003eRequireScopePlug\u003c/code\u003e built the \u003ccode\u003eBearer resource_metadata=\"...\"\u003c/code\u003e challenge by interpolating a \u003ccode\u003eresource_metadata\u003c/code\u003e URL derived from the request tenant directly into the quoted value. In a multi-tenant application that sets the Ash tenant from request-controlled data (a subdomain, the \u003ccode\u003eHost\u003c/code\u003e, a path segment, or a header), a tenant containing a \u003ccode\u003e\"\u003c/code\u003e closes the quoted value and appends attacker-chosen auth-params, including a second \u003ccode\u003eresource_metadata\u003c/code\u003e URL pointing at an attacker-controlled authorization server that spec-following clients follow. Carriage returns and line feeds are rejected by Plug, so this is parameter injection within one header, not response splitting.\u003c/p\u003e\n\u003cp\u003eThis issue affects ash_authentication_oauth2_server: from 0.1.3 before 0.3.1.\u003c/p\u003e"
},
{
"base64": false,
"type": "text/markdown",
"value": "Improper Encoding or Escaping of Output vulnerability in ash-project ash_authentication_oauth2_server allows an unauthenticated attacker to inject arbitrary authentication parameters into the `WWW-Authenticate` challenge header.\n\n`BearerPlug` and `RequireScopePlug` built the `Bearer resource_metadata=\"...\"` challenge by interpolating a `resource_metadata` URL derived from the request tenant directly into the quoted value. In a multi-tenant application that sets the Ash tenant from request-controlled data (a subdomain, the `Host`, a path segment, or a header), a tenant containing a `\"` closes the quoted value and appends attacker-chosen auth-params, including a second `resource_metadata` URL pointing at an attacker-controlled authorization server that spec-following clients follow. Carriage returns and line feeds are rejected by Plug, so this is parameter injection within one header, not response splitting.\n\nThis issue affects ash_authentication_oauth2_server: from 0.1.3 before 0.3.1."
}
],
"value": "Improper Encoding or Escaping of Output vulnerability in ash-project ash_authentication_oauth2_server allows an unauthenticated attacker to inject arbitrary authentication parameters into the WWW-Authenticate challenge header.\n\nBearerPlug and RequireScopePlug built the Bearer resource_metadata=\"...\" challenge by interpolating a resource_metadata URL derived from the request tenant directly into the quoted value. In a multi-tenant application that sets the Ash tenant from request-controlled data (a subdomain, the Host, a path segment, or a header), a tenant containing a \" closes the quoted value and appends attacker-chosen auth-params, including a second resource_metadata URL pointing at an attacker-controlled authorization server that spec-following clients follow. Carriage returns and line feeds are rejected by Plug, so this is parameter injection within one header, not response splitting.\n\nThis issue affects ash_authentication_oauth2_server: from 0.1.3 before 0.3.1."
}
],
"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": "LOW",
"subIntegrityImpact": "LOW",
"userInteraction": "NONE",
"valueDensity": "NOT_DEFINED",
"vectorString": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:L/SI:L/SA:N",
"version": "4.0",
"vulnAvailabilityImpact": "NONE",
"vulnConfidentialityImpact": "NONE",
"vulnIntegrityImpact": "LOW",
"vulnerabilityResponseEffort": "NOT_DEFINED"
},
"format": "CVSS",
"scenarios": [
{
"lang": "en",
"value": "GENERAL"
}
]
}
],
"problemTypes": [
{
"descriptions": [
{
"cweId": "CWE-116",
"description": "CWE-116 Improper Encoding or Escaping of Output",
"lang": "en",
"type": "CWE"
}
]
}
],
"providerMetadata": {
"dateUpdated": "2026-09-07T22:30:55.280Z",
"orgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"shortName": "EEF"
},
"references": [
{
"tags": [
"vendor-advisory",
"related"
],
"url": "https://github.com/ash-project/ash_authentication_oauth2_server/security/advisories/GHSA-2h3v-83jg-2qmm"
},
{
"tags": [
"related"
],
"url": "https://cna.erlef.org/cves/CVE-2026-82756.html"
},
{
"tags": [
"related"
],
"url": "https://osv.dev/vulnerability/EEF-CVE-2026-82756"
},
{
"tags": [
"patch"
],
"url": "https://github.com/ash-project/ash_authentication_oauth2_server/commit/09f97476715da031b136eaec7b2cda2363ad8149"
}
],
"source": {
"discovery": "EXTERNAL"
},
"title": "ash_authentication_oauth2_server interpolates a tenant-derived value into the WWW-Authenticate challenge without escaping, allowing header parameter injection"
}
},
"cveMetadata": {
"assignerOrgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"assignerShortName": "EEF",
"cveId": "CVE-2026-82756",
"datePublished": "2026-09-07T22:30:55.280Z",
"dateReserved": "2026-08-31T01:00:10.817Z",
"dateUpdated": "2026-09-08T14:43:33.571Z",
"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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