CVE-2026-82754

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CVE-2026-82754

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

Details: 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.

References: https://cna.erlef.org/cves/CVE-2026-82754.html, https://github.com, https://osv.dev/vulnerability/EEF-CVE-2026-82754, https://repo.hex.pm, https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/82xxx/CVE-2026-82754.json, https://github.com/ash-project/ash_authentication_oauth2_server/security/advisories/GHSA-wwxg-h779-3wf4, https://nvd.nist.gov/vuln/detail/CVE-2026-82754, https://github.com/ash-project/ash_authentication_oauth2_server/commit/a72972d7ed3eb74c05dfa0653a258ef14454459a, https://github.com/ash-project/ash_authentication_oauth2_server