---
id: CVE-2026-82756
title: >-
  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.


  BearerPlu…
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.


  BearerPlu…
severity: medium
cvss: 6.3
cvssVector: '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'
cwe:
  - CWE-116
vendor: ash-project
product: ash_authentication_oauth2_server
affected:
  - ash_authentication_oauth2_server >= 0.1.3 < 0.3.1
  - >-
    ash-project/ash_authentication_oauth2_server >=
    99de0a1cacb5ef667c4533278b7c81ca98c00231 <
    09f97476715da031b136eaec7b2cda2363ad8149
published: '2026-09-07'
updated: '2026-09-08'
sourceUpdated: '2026-09-08T15:18:50.653'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-82756'
references:
  - url: 'https://cna.erlef.org/cves/CVE-2026-82756.html'
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: >-
      https://github.com/ash-project/ash_authentication_oauth2_server/commit/09f97476715da031b136eaec7b2cda2363ad8149
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: >-
      https://github.com/ash-project/ash_authentication_oauth2_server/security/advisories/GHSA-2h3v-83jg-2qmm
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: 'https://osv.dev/vulnerability/EEF-CVE-2026-82756'
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
tags:
  - nvd
  - cve.org
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-09-08T14:43:23.093058Z'
cvssSource: cna
epss: 0.0068
epssPercentile: 0.50325
ingestedAt: '2026-09-08T15:33:26.980Z'
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.