CVE-2026-82755 Information disclosure in ash authentication oauth2 server
A shared HTTP cache may serve one tenant's OAuth metadata to another, causing clients to send secrets to the wrong endpoint or validate tokens incorrectly.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-82755?
CVE-2026-82755 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
Use of Cache Containing Sensitive Information vulnerability in ash-project ash_authentication_oauth2_server allows a shared HTTP cache to serve one tenant's OAuth discovery metadata to another tenant's clients.
The RFC 8414 and RFC 9728 metadata endpoints in AshAuthentication.Phoenix.Oauth2Server.ProtocolRouter return tenant-specific values (issuer, authorization_endpoint, token_endpoint, jwks_uri) when a tenant is set, but sent them with Cache-Control: public, max-age=3600 and no Vary. When the tenant is derived from something other than the URL (a header or the Host) and a shared cache sits in front, the cache key is the URL alone, so a stored response for one tenant is served to another for up to an hour. Affected clients may then send authorization codes and secrets to the wrong tenant's token endpoint and validate tokens against the wrong keys.
This issue affects ash_authentication_oauth2_server: from 0.1.3 before 0.3.1.
Weakness: CWE-524
Which versions are affected by CVE-2026-82755?
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-2026-82755?
Upgrade ash_authentication_oauth2_server to 0.3.1 or later.
Is CVE-2026-82755 being exploited?
There is no known exploitation of CVE-2026-82755 in the wild and no public exploit code.
Sources
Also known as EEF-CVE-2026-82755, GHSA-crqf-7m54-4hgc.