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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\"NONE\", \"vulnerabilityResponseEffort\": \"NOT_DEFINED\"}, \"scenarios\": [{\"lang\": \"en\", \"value\": \"GENERAL\"}]}], \"affected\": [{\"cpes\": [\"cpe:2.3:a:ash-project:ash_authentication_oauth2_server:*:*:*:*:*:*:*:*\"], \"repo\": \"https://github.com/ash-project/ash_authentication_oauth2_server\", \"vendor\": \"ash-project\", \"modules\": [\"\u0027Elixir.AshAuthentication.Phoenix.Oauth2Server.BearerPlug\u0027\", \"\u0027Elixir.AshAuthentication.Phoenix.Oauth2Server.RequireScopePlug\u0027\"], \"product\": \"ash_authentication_oauth2_server\", \"versions\": [{\"status\": \"affected\", \"version\": \"0.1.3\", \"lessThan\": \"0.3.1\", \"versionType\": \"semver\"}], \"packageURL\": \"pkg:hex/ash_authentication_oauth2_server\", \"packageName\": \"ash_authentication_oauth2_server\", \"programFiles\": [\"lib/ash_authentication_phoenix/oauth2_server/bearer_plug.ex\", \"lib/ash_authentication_phoenix/oauth2_server/require_scope_plug.ex\"], \"collectionURL\": \"https://repo.hex.pm\", \"defaultStatus\": \"unaffected\", \"programRoutines\": [{\"name\": \"\u0027Elixir.AshAuthentication.Phoenix.Oauth2Server.BearerPlug\u0027:call/2\"}, {\"name\": \"\u0027Elixir.AshAuthentication.Phoenix.Oauth2Server.RequireScopePlug\u0027:call/2\"}]}, {\"cpes\": [\"cpe:2.3:a:ash-project:ash_authentication_oauth2_server:*:*:*:*:*:*:*:*\"], \"repo\": \"https://github.com/ash-project/ash_authentication_oauth2_server\", \"vendor\": \"ash-project\", \"modules\": [\"\u0027Elixir.AshAuthentication.Phoenix.Oauth2Server.BearerPlug\u0027\", \"\u0027Elixir.AshAuthentication.Phoenix.Oauth2Server.RequireScopePlug\u0027\"], \"product\": \"ash_authentication_oauth2_server\", \"versions\": [{\"status\": \"affected\", \"version\": \"99de0a1cacb5ef667c4533278b7c81ca98c00231\", \"lessThan\": \"09f97476715da031b136eaec7b2cda2363ad8149\", \"versionType\": \"git\"}], \"packageURL\": \"pkg:github/ash-project/ash_authentication_oauth2_server\", \"packageName\": \"ash-project/ash_authentication_oauth2_server\", \"programFiles\": [\"lib/ash_authentication_phoenix/oauth2_server/bearer_plug.ex\", \"lib/ash_authentication_phoenix/oauth2_server/require_scope_plug.ex\"], \"collectionURL\": \"https://github.com\", \"defaultStatus\": \"unaffected\", \"programRoutines\": [{\"name\": \"\u0027Elixir.AshAuthentication.Phoenix.Oauth2Server.BearerPlug\u0027:call/2\"}, {\"name\": \"\u0027Elixir.AshAuthentication.Phoenix.Oauth2Server.RequireScopePlug\u0027:call/2\"}]}], \"references\": [{\"url\": \"https://github.com/ash-project/ash_authentication_oauth2_server/security/advisories/GHSA-2h3v-83jg-2qmm\", \"tags\": [\"vendor-advisory\", \"related\"]}, {\"url\": \"https://cna.erlef.org/cves/CVE-2026-82756.html\", \"tags\": [\"related\"]}, {\"url\": \"https://osv.dev/vulnerability/EEF-CVE-2026-82756\", \"tags\": [\"related\"]}, {\"url\": \"https://github.com/ash-project/ash_authentication_oauth2_server/commit/09f97476715da031b136eaec7b2cda2363ad8149\", \"tags\": [\"patch\"]}], \"descriptions\": [{\"lang\": \"en\", \"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.\", \"supportingMedia\": [{\"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.\", \"base64\": false}]}], \"problemTypes\": [{\"descriptions\": [{\"lang\": \"en\", \"type\": \"CWE\", \"cweId\": \"CWE-116\", \"description\": \"CWE-116 Improper Encoding or Escaping of Output\"}]}], \"configurations\": [{\"lang\": \"en\", \"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.\", \"supportingMedia\": [{\"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`.\", \"base64\": false}]}], \"cpeApplicability\": [{\"nodes\": [{\"negate\": false, \"cpeMatch\": [{\"criteria\": \"cpe:2.3:a:ash-project:ash_authentication_oauth2_server:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"0.3.1\", \"versionStartIncluding\": \"0.1.3\"}], \"operator\": \"OR\"}], \"operator\": \"AND\"}], \"providerMetadata\": {\"orgId\": \"6b3ad84c-e1a6-4bf7-a703-f496b71e49db\", \"shortName\": \"EEF\", \"dateUpdated\": \"2026-09-07T22:30:55.280Z\"}}}",
"cveMetadata": "{\"cveId\": \"CVE-2026-82756\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-09-08T14:43:33.571Z\", \"dateReserved\": \"2026-08-31T01:00:10.817Z\", \"assignerOrgId\": \"6b3ad84c-e1a6-4bf7-a703-f496b71e49db\", \"datePublished\": \"2026-09-07T22:30:55.280Z\", \"assignerShortName\": \"EEF\"}",
"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.
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.
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