# CVE-2026-76835: OAuth2 Proxy authentication bypass via X-Forwarded-Uri spoofing

Source: https://junglewise.ai/threats/cve-2026-40575-oauth2-proxy-authentication-bypass-via-x-forwarded-uri-spoofing  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-04-22. Updated: 2026-07-21  
License: CC BY 4.0 with a link back

CVE-2026-76835 · Severity: critical · CVSS 9.1 · Published 2026-04-22

OAuth2 Proxy, a tool used to provide authentication for web applications, contains a flaw that allows attackers to bypass security checks. By sending specially crafted web requests, an unauthorized user can trick the system into granting access to protected areas without a valid login. This could lead to the exposure of sensitive internal data or unauthorized access to corporate applications.

Technologies: [github.com/oauth2-proxy/oauth2-proxy (Go)](https://junglewise.ai/threats/technologies/github-com-oauth2-proxy-oauth2-proxy), [github.com/oauth2-proxy/oauth2-proxy/v7 (Go)](https://junglewise.ai/threats/technologies/github-com-oauth2-proxy-oauth2-proxy-v7), [OAuth2 Proxy](https://junglewise.ai/threats/technologies/oauth2-proxy). Vendors: [Go](https://junglewise.ai/threats/vendors/go), [OAuth2 Proxy](https://junglewise.ai/threats/vendors/oauth2-proxy).

## Quick answers

**Is CVE-2026-76835 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-76835 being exploited in the wild.

**How severe is CVE-2026-76835?** Critical severity, with a CVSS score of 9.1, published 22 April 2026.

**Which products and versions are affected?** github.com/oauth2-proxy/oauth2-proxy (Go) SEMVER:introduced=0; github.com/oauth2-proxy/oauth2-proxy/v7 (Go) >= 7.5.0, < 7.15.2, SEMVER:introduced=7.5.0,fixed=7.15.2; OAuth2 Proxy >= 7.5.0, < 7.15.2.

**Is there a fix for CVE-2026-76835?** Yes. github.com/oauth2-proxy/oauth2-proxy/v7 (Go): upgrade to 7.15.2 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-76835 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-76835?** Check whether you run github.com/oauth2-proxy/oauth2-proxy (Go), github.com/oauth2-proxy/oauth2-proxy/v7 (Go) or OAuth2 Proxy at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- github.com/oauth2-proxy/oauth2-proxy/v7 (Go): upgrade to 7.15.2 or later

  ```sh
  go get github.com/oauth2-proxy/oauth2-proxy/v7@v7.15.2
  ```


## Technical details

An authentication bypass (CWE-290) exists in OAuth2 Proxy due to improper handling of the X-Forwarded-Uri header. When the --reverse-proxy flag is enabled alongside --skip_auth_routes or --skip-auth-regex, the application may trust client-supplied headers to evaluate authentication rules. An unauthenticated remote attacker can spoof this header to make the proxy believe the request is for a path that does not require authentication, while the request is actually forwarded to a protected upstream path. The issue is addressed in version 7.15.2 by introducing the --trusted-proxy-ip flag to restrict which source IPs can provide forwarded headers.

## Affected products

- OAuth2 Proxy OAuth2 Proxy >= 7.5.0, < 7.15.2

## Identifiers

- CVE-2026-76835
- CVE-2026-40575
- GHSA-7x63-xv5r-3p2x
- GO-2026-5236

## Timeline

- 2026-04-14: disclosed: Reported to oauth2-proxy/oauth2-proxy
- 2026-04-15: advisory: GitHub Advisory published
- 2026-04-22: other: Published to NVD

## References

- [https://api.github.com/users/iamnoooob](https://api.github.com/users/iamnoooob)
- [https://github.com/iamnoooob](https://github.com/iamnoooob)
- [https://api.github.com/users/iamnoooob/gists%7B/gist_id%7D](https://api.github.com/users/iamnoooob/gists%7B/gist_id%7D)
- [https://api.github.com/users/iamnoooob/repos](https://api.github.com/users/iamnoooob/repos)
- [https://avatars.githubusercontent.com/u/31939327?v=4](https://avatars.githubusercontent.com/u/31939327?v=4)
- [https://api.github.com/users/iamnoooob/events%7B/privacy%7D](https://api.github.com/users/iamnoooob/events%7B/privacy%7D)

## Related threats

- [OAuth2 Proxy authentication bypass via spoofed X-Forwarded-Uri header](https://junglewise.ai/threats/cve-2026-76835-oauth2-proxy-authentication-bypass-via-spoofed-x-forwarded-uri)
- [OAuth2 Proxy has an Authentication Bypass via Fragment Confusion in skip_auth_routes and skip_auth_regex](https://junglewise.ai/threats/cve-2026-41059-oauth2-proxy-has-an-authentication-bypass-via-fragment-confusion)
- [OAuth2 Proxy has an Authorization Bypass in Email Domain Validation via Malformed Multi-@ Email Claims](https://junglewise.ai/threats/cve-2026-40574-oauth2-proxy-has-an-authorization-bypass-in-email-domain)
- [OAuth2 Proxy authentication bypass via health check User-Agent spoofing](https://junglewise.ai/threats/cve-2026-34457-oauth2-proxy-authentication-bypass-via-health-check-user-agent)
- [OAuth2 Proxy insufficient session expiration in sign-in page handler](https://junglewise.ai/threats/cve-2026-34454-oauth2-proxy-insufficient-session-expiration-in-sign-in-page)