CVE-2026-82756

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.

CVSS

No CVSS.

References

Link	Resource
https://cna.erlef.org/cves/CVE-2026-82756.html
https://github.com/ash-project/ash_authentication_oauth2_server/commit/09f97476715da031b136eaec7b2cda2363ad8149
https://github.com/ash-project/ash_authentication_oauth2_server/security/advisories/GHSA-2h3v-83jg-2qmm
https://osv.dev/vulnerability/EEF-CVE-2026-82756

Configurations

No configuration.

History

No history.

Information

Published : 2026-09-07 23:16

Updated : 2026-09-08 15:18

NVD link : CVE-2026-82756

Mitre link : CVE-2026-82756

CVE.ORG link : CVE-2026-82756

JSON object : View

Products Affected

No product.

CWE

CWE-116

Improper Encoding or Escaping of Output

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["cpe:2.3:a:ash-project:ash_authentication_oauth2_server:*:*:*:*:*:*:*:*"], "repo": "https://github.com/ash-project/ash_authentication_oauth2_server", "vendor": "ash-project", "modules": ["'Elixir.AshAuthentication.Phoenix.Oauth2Server.BearerPlug'", "'Elixir.AshAuthentication.Phoenix.Oauth2Server.RequireScopePlug'"], "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": "'Elixir.AshAuthentication.Phoenix.Oauth2Server.BearerPlug':call/2"}, {"name": "'Elixir.AshAuthentication.Phoenix.Oauth2Server.RequireScopePlug':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": ["'Elixir.AshAuthentication.Phoenix.Oauth2Server.BearerPlug'", "'Elixir.AshAuthentication.Phoenix.Oauth2Server.RequireScopePlug'"], "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": "'Elixir.AshAuthentication.Phoenix.Oauth2Server.BearerPlug':call/2"}, {"name": "'Elixir.AshAuthentication.Phoenix.Oauth2Server.RequireScopePlug':call/2"}]}]}], "published": "2026-09-07T23:16:52.770", "references": [{"url": "https://cna.erlef.org/cves/CVE-2026-82756.html", "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db"}, {"url": "https://github.com/ash-project/ash_authentication_oauth2_server/commit/09f97476715da031b136eaec7b2cda2363ad8149", "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db"}, {"url": "https://github.com/ash-project/ash_authentication_oauth2_server/security/advisories/GHSA-2h3v-83jg-2qmm", "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db"}, {"url": "https://osv.dev/vulnerability/EEF-CVE-2026-82756", "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db"}], "vulnStatus": "Deferred", "weaknesses": [{"type": "Secondary", "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "description": [{"lang": "en", "value": "CWE-116"}]}], "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."}], "lastModified": "2026-09-08T15:18:50.653", "sourceIdentifier": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db"}