---
id: CVE-2026-40574
aliases:
  - GHSA-c5c4-8r6x-56w3
  - BIT-oauth2-proxy-2026-40574
  - GO-2026-5314
title: >-
  OAuth2 Proxy has an Authorization Bypass in Email Domain Validation via
  Malformed Multi-@ Email Claims
summary: >-
  OAuth2 Proxy has an Authorization Bypass in Email Domain Validation via
  Malformed Multi-@ Email Claims
severity: medium
cvss: 6.8
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N'
vendor: oauth2-proxy
product: github.com/oauth2-proxy/oauth2-proxy/v7
ecosystem: go
affected:
  - github.com/oauth2-proxy/oauth2-proxy/v7 < 7.15.2
patched:
  - github.com/oauth2-proxy/oauth2-proxy/v7 7.15.2
published: '2026-04-15'
updated: '2026-07-21'
source: OSV
sourceUrl: 'https://osv.dev/vulnerability/GHSA-c5c4-8r6x-56w3'
references:
  - url: >-
      https://github.com/oauth2-proxy/oauth2-proxy/security/advisories/GHSA-c5c4-8r6x-56w3
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-40574'
  - url: 'https://github.com/oauth2-proxy/oauth2-proxy'
tags:
  - osv
  - go
epss: 0.00209
epssPercentile: 0.1131
ingestedAt: '2026-07-21T19:04:58.697Z'
---

## Overview

### Impact

An authorization bypass exists in OAuth2 Proxy as part of the `email_domain` enforcement option. An attacker may be able to authenticate with an email claim such as `attacker@evil.com@company.com` and satisfy an allowed domain check for `company.com`, even though the claim is not a valid email address.

The issue **ONLY** affects deployments that rely on `email_domain` restrictions and accept email claim values from identity providers or claim mappings that do not strictly enforce normal email syntax. The practical risk ONLY exists in self-hosted or custom OIDC environments and federated setups where unexpected claim values can reach oauth2-proxy. Standard hosted providers that enforce valid email formatting ARE NOT effected.

### Patches
Users should upgrade to `v7.15.2` or later once available.

### Workarounds
The most effective workaround is to ensure the configured identity provider cannot emit malformed or attacker-controlled email claim values.

## Affected packages

- `github.com/oauth2-proxy/oauth2-proxy/v7 < 7.15.2`

## Remediation

Upgrade to a patched release:

- `github.com/oauth2-proxy/oauth2-proxy/v7 7.15.2`