---
id: CVE-2026-82754
title: >-
  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_ser…
summary: >-
  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_ser…
severity: medium
cvss: 6.3
cvssVector: '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
vendor: ash-project
product: ash_authentication_oauth2_server
affected:
  - ash_authentication_oauth2_server >= 0.1.0 < 0.3.1
  - >-
    ash-project/ash_authentication_oauth2_server >=
    855b578037c5ded18e8a6e60f42e56bde4905fae <
    a72972d7ed3eb74c05dfa0653a258ef14454459a
published: '2026-09-07'
updated: '2026-09-08'
sourceUpdated: '2026-09-08T15:18:50.320'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-82754'
references:
  - url: 'https://cna.erlef.org/cves/CVE-2026-82754.html'
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: >-
      https://github.com/ash-project/ash_authentication_oauth2_server/commit/a72972d7ed3eb74c05dfa0653a258ef14454459a
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: >-
      https://github.com/ash-project/ash_authentication_oauth2_server/security/advisories/GHSA-wwxg-h779-3wf4
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: 'https://osv.dev/vulnerability/EEF-CVE-2026-82754'
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
tags:
  - nvd
  - cve.org
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-09-08T14:41:33.862078Z'
cvssSource: cna
epss: 0.00691
epssPercentile: 0.5079
ingestedAt: '2026-09-08T15:33:26.980Z'
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.