CVE-2026-82756ash_authentication_oauth2_server interpolates a tenant-derived value into the WWW-Authenticate challenge without escaping, allowing header parameter injection

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

6.3 MEDIUM (v4.0, CNA)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

Weakness (CWE)

CWE-116

Known exploited

Not in CISA's KEV catalog

EPSS (exploitation in the next 30 days)

Not loaded for this CVE

Assigned by

EEF

NVD analysis

Deferred

Record last updated

Sep 8, 2026

First seen by InfoSec Signals

Oct 9, 2026

The CVE record on cve.org · NVD's entry

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