CVE-2026-82756: Ash-Project Ash Authentication OAUTH2 Server

Medium severity, CVSS 6.3. EPSS: 0.7% chance of exploitation in the next 30 days.

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.

Affected products

• Ash-Project Ash Authentication OAUTH2 Server: from 0.1.3, before 0.3.1 (fixed in 0.3.1)

Published 2026-09-07. Last modified 2026-09-08.