CVE-2026-82754: ash_authentication_oauth2_server aliases every protocol endpoint under /.well-known, bypassing path-scoped controls

Severity: medium (CVSS 6.3 v4.0)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.7% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-09-07 · updated 2026-09-08
Weakness: CWE-424

Description

Improper Protection of Alternate Path vulnerability in ash-project ash_authentication_oauth2_server exposes the state-changing OAuth endpoints under an unintended URL prefix, bypassing controls scoped to the canonical prefix. oauth2_server_protocol_routes/1 in AshAuthentication.Phoenix.Oauth2Server.Router forwards the same ProtocolRouter at both the /oauth prefix and the /.well-known prefix. Phoenix forward strips the matched prefix before dispatch, so the full route table answers under both mounts, and POST /register, POST /token, and POST /revoke are reachable as /.well-known/register, /.well-known/token, and /.well-known/revoke. Edge controls such as WAF rules, rate limits, or authentication exemptions written against the /oauth paths, or that allow-list /.well-known as unauthenticated, do not apply to the alias. This issue affects ash_authentication_oauth2_server: from 0.1.0 before 0.3.1.

Affected products

ash-project ash_authentication_oauth2_server: from 0.1.0 before 0.3.1 — fixed in 0.3.1

How to fix

Upgrade to a fixed version: ash-project ash_authentication_oauth2_server 0.3.1. Check the vendor advisory for mitigations.

References

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