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.

Attack Vector Network

Attack Complexity Low

Privileges Required None

Attack Requirements Present

User Interaction None

Vulnerable System Confidentiality Impact None

Vulnerable System Integrity Impact Low

Vulnerable System Availability Impact None

Subsequent System Confidentiality Impact Low

Subsequent System Integrity Impact Low

Subsequent System Availability Impact None

No CVSS v3.1

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

The EPSS score is 0.00378.

Exploitation none

Automatable no

Technical Impact partial

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions
ash-project ash_authentication_oauth2_server unaffected
Version Status Constraints
0.1.3 affected < 0.3.1
ash-project ash_authentication_oauth2_server unaffected
Version Status Constraints
99de0a1cacb5ef667c4533278b7c81ca98c00231 affected < 09f97476715da031b136eaec7b2cda2363ad8149

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Project Subscriptions

Vendors Products
Ash-project Subscribe
Ash Authentication Oauth2 Server Subscribe
Advisories

No advisories yet.

Fixes

Solution

No solution given by the vendor.

Workaround

No workaround given by the vendor.

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

Tue, 08 Sep 2026 15:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Mon, 07 Sep 2026 22:45:00 +0000

Type Values Removed Values Added
Description 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.
Title ash_authentication_oauth2_server interpolates a tenant-derived value into the WWW-Authenticate challenge without escaping, allowing header parameter injection
First Time appeared Ash-project
Ash-project ash Authentication Oauth2 Server
Weaknesses CWE-116
CPEs cpe:2.3:a:ash-project:ash_authentication_oauth2_server:*:*:*:*:*:*:*:*
Vendors & Products Ash-project
Ash-project ash Authentication Oauth2 Server
References
Metrics cvssV4_0

{'score': 6.3, 'vector': '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'}

Projects

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cve-icon MITRE

Status: PUBLISHED

Assigner: EEF

Published:

Updated: 2026-09-08T14:43:33.571Z

Reserved: 2026-08-31T01:00:10.817Z

Link: CVE-2026-82756

cve-icon Vulnrichment

Updated: 2026-09-08T14:43:29.441Z

cve-icon NVD

Status : Deferred

Published: 2026-09-07T23:16:52.770

Modified: 2026-09-08T15:18:50.653

Link: CVE-2026-82756

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-09-08T00:00:11Z

Weaknesses