---
id: CVE-2026-76835
title: >-
  OAuth2 Proxy honours a client-supplied X-Forwarded-Uri header when deciding
  whether a request may skip authentication, because the guard added for
  CVE-2026-40575 is inert in the default reverse-proxy configuration
summary: >-
  OAuth2 Proxy honours a client-supplied X-Forwarded-Uri header when deciding
  whether a request may skip authentication, because the guard added for
  CVE-2026-40575 is inert in the default reverse-proxy configuration.
  GetRequestURI in pkg/r…
severity: critical
cvss: 9.1
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N'
cwe:
  - CWE-290
published: '2026-08-24'
updated: '2026-09-24'
sourceUpdated: '2026-09-24T20:43:32.537'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-76835'
references:
  - url: 'https://github.com/oauth2-proxy/oauth2-proxy'
    label: disclosure@vulncheck.com
  - url: >-
      https://github.com/oauth2-proxy/oauth2-proxy/blob/v7.15.4/pkg/apis/middleware/scope.go
    label: disclosure@vulncheck.com
  - url: 'https://github.com/oauth2-proxy/oauth2-proxy/issues/3506'
    label: disclosure@vulncheck.com
  - url: >-
      https://github.com/oauth2-proxy/oauth2-proxy/security/advisories/GHSA-7x63-xv5r-3p2x
    label: disclosure@vulncheck.com
  - url: >-
      https://www.vulncheck.com/advisories/oauth2-proxy-through-authentication-bypass-via-x-forwarded-uri-under-the-default-trusted-proxy-set
    label: disclosure@vulncheck.com
  - url: 'https://github.com/oauth2-proxy/oauth2-proxy/issues/3506'
    label: 134c704f-9b21-4f2e-91b3-4a467353bcc0
tags:
  - nvd
epss: 0.00629
epssPercentile: 0.47846
ingestedAt: '2026-09-24T20:51:40.224Z'
---

## Overview

OAuth2 Proxy honours a client-supplied X-Forwarded-Uri header when deciding whether a request may skip authentication, because the guard added for CVE-2026-40575 is inert in the default reverse-proxy configuration. GetRequestURI in pkg/requests/util/util.go prefers that header over the real request URI whenever CanTrustForwardedHeaders returns true, and isAllowedPath in oauthproxy.go matches the skip_auth_routes and skip_auth_regex allow list against the resulting path. CanTrustForwardedHeaders in pkg/apis/middleware/scope.go grants that trust when the caller's address is in the trusted proxy set, and buildTrustedProxyNetSet falls back to defaultTrustedProxyIPs, which is 0.0.0.0/0 and ::/0, whenever reverse proxy mode is enabled without trusted_proxy_ip configured. Every client is therefore treated as a trusted proxy. An unauthenticated attacker can request a protected upstream path while setting X-Forwarded-Uri to a value matching an allow-listed route, so the skip-auth decision is made against the spoofed value while the upstream receives the protected path unchanged.

## Remediation

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