CVE-2026-82755
ash_authentication_oauth2_server serves tenant-specific OAuth metadata as publicly cacheable without Vary, enabling cross-tenant confusion
- State
- Published
- Severity
- 6.3 Medium
- Published
- Sep 7, 2026
- Updated
- Sep 8, 2026
- Reserved
- Aug 31, 2026
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.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 4.0 | 6.3 Medium | CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:L/SI:L/SA:N | EEF |
Weaknesses
- CWE-524 Use of Cache Containing Sensitive Information
Affected Products
| Product | Versions |
|---|---|
ash_authentication_oauth2_serverash-project |
|
ash_authentication_oauth2_serverash-project |
|
References
- https://github.com/ash-project/ash_authentication_oauth2_server/security/advisories/GHSA-crqf-7m54-4hgcvendor-advisoryrelated
- https://cna.erlef.org/cves/CVE-2026-82755.htmlrelated
- https://osv.dev/vulnerability/EEF-CVE-2026-82755related
- https://github.com/ash-project/ash_authentication_oauth2_server/commit/768d87f70e4e97ae1d2bf1606b5bf3f4d03f24a1patch
Every record here comes from the CVE Program’s CVE List. © 1999–2026 The MITRE Corporation. CVE is a registered trademark of The MITRE Corporation. The records are reproduced under the CVE Program terms of use.