# CVE-2026-82754

## Summary

- **CVE ID:** CVE-2026-82754
- **Severity:** MEDIUM
- **CVSS Score:** 6.3 (CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N)
- **CWE:** CWE-424
- **Published:** Sep 7, 2026
- **Last Modified:** Sep 8, 2026

## 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 (0.1.0)
- ash-project — ash_authentication_oauth2_server (855b578037c5ded18e8a6e60f42e56bde4905fae)

## References

- [CNA](https://github.com/ash-project/ash_authentication_oauth2_server/security/advisories/GHSA-wwxg-h779-3wf4)
- [CNA](https://cna.erlef.org/cves/CVE-2026-82754.html)
- [CNA](https://osv.dev/vulnerability/EEF-CVE-2026-82754)
- [CNA](https://github.com/ash-project/ash_authentication_oauth2_server/commit/a72972d7ed3eb74c05dfa0653a258ef14454459a)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.39%
- **EPSS Percentile:** 31.8

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-11._