CVE-2026-82755mediumCWE-524

CVE-2026-82755: medium-severity vulnerability in ash-project ash_authentication_oauth2_server

ash_authentication_oauth2_server serves tenant-specific OAuth metadata as publicly cacheable without Vary, enabling cross-tenant confusion

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13Vexday Risk Score

No sign of exploitation. No public exploitation artifact known so far.

ssvc Trackcvss 6.3epss 0.7%
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.
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
Affected products
ash-project · ash_authentication_oauth2_server
Related CVEs — ash-project ash_authentication_oauth2_server

In the same product, most dangerous first.

CVE-2026-82754MEDIUMash_authentication_oauth2_server aliases every protocol endpoint under /.well-known, bypassing path-scoped controlsEPSS 0.7%CVE-2026-82758MEDIUMash_authentication_oauth2_server treats an empty resolved secret as valid, opening the gated Dynamic Client Registration endpointEPSS 0.7%CVE-2026-82756MEDIUMash_authentication_oauth2_server interpolates a tenant-derived value into the WWW-Authenticate challenge without escaping, allowing header parameter injectionEPSS 0.7%CVE-2026-82757MEDIUMash_authentication_oauth2_server CIMD fetcher classifies IPv4-in-IPv6 and site-local addresses as public, allowing SSRFEPSS 0.7%CVE-2026-82753HIGHUnauthenticated authorize requests create unbounded, never-expiring CIMD client rows and cache entries in ash_authentication_oauth2_serverEPSS 0.7%