CVE-2026-82756 Other in ash authentication oauth2 server
An attacker can inject malicious authentication parameters into the WWW-Authenticate header in multi-tenant setups, potentially redirecting clients to attacker-controlled servers.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-82756?
CVE-2026-82756 is a medium-severity vulnerability in ash-project ash_authentication_oauth2_server, published on 7 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-116
Which versions are affected by CVE-2026-82756?
1 open source package ship an affected version, including ash_authentication_oauth2_server.
| Package | Affected | Fixed in |
|---|---|---|
ash_authentication_oauth2_server Hex | From 0.1.3 | 0.3.1 |
How do I fix CVE-2026-82756?
Upgrade ash_authentication_oauth2_server to 0.3.1 or later.
Is CVE-2026-82756 being exploited?
There is no known exploitation of CVE-2026-82756 in the wild and no public exploit code.
Sources
Also known as EEF-CVE-2026-82756, GHSA-2h3v-83jg-2qmm.