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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Drag nodes to arrange them. Double-click a related vulnerability to open it, or a source to visit its link. The Physics button on the left tunes the layout and the simulation; the legend at the bottom left hides or shows nodes by kind and by sighting type.
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.
Vulnerability timeline
Sightings and recorded dates, grouped by day · UTC
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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.