OAuth2 Proxy has an Authentication Bypass via X-Forwarded-Uri Header Spoofing

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

9.1 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

EPSS

• CVE-2026-40575: 0.48% estimated exploitation activity in the next 30 days; percentile 41.26 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Impact A configuration-dependent authentication bypass exists in OAuth2 Proxy. Deployments are affected when all of the following are true: OAuth2 Proxy is configured with --reverse-proxy and at least one rule is defined with --skipauthroutes or the legacy --skip-auth-regex OAuth2 Proxy may trust a client-supplied X-Forwarded-Uri header when --reverse-proxy is enabled and --skip-auth-route or --skip-auth-regex 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. Patches This issue is addressed as part of the newly introduced --trusted-proxy-ip flag in v7.15.2. If you leave it unset, OAuth2 Proxy will continue to trust ALL source IPs (0.0.0.0/0) for backwards compatibility, which means a client may still be able to…

Published by the source

15 Apr 2026, 19:21 UTC

Last modified by the source

21 Jul 2026, 13:50 UTC

Source last checked

26 Oct 2026, 15:27 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-7x63-xv5r-3p2x

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# Patch Next advisory brief: CVE-2026-40575

Advisory: OAuth2 Proxy has an Authentication Bypass via X-Forwarded-Uri Header Spoofing
IDs: CVE-2026-40575, GHSA-7x63-xv5r-3p2x
Record: https://patchnext.com/advisories/cve-2026-40575 (revision 1, source checked 26 Oct 2026, 15:27 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Critical (CVSS 9.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/oauth2-proxy/oauth2-proxy/v7 7.15.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/oauth2-proxy/oauth2-proxy/v7: affected >= 7.5.0, < 7.15.2; fixed in 7.15.2

## Suggested inspection (read-only)
- Go github.com/oauth2-proxy/oauth2-proxy/v7: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/oauth2-proxy/oauth2-proxy/v7.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-7x63-xv5r-3p2x (GitHub-reviewed advisory GHSA-7x63-xv5r-3p2x lists affected ranges: Go github.com/oauth2-proxy/oauth2-proxy/v7 >=7.5.0 <7.15.2)

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