OAuth2 Proxy has an Authorization Bypass in Email Domain Validation via Malformed Multi-@ Email Claims

Exploitation

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

CVSS

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

EPSS

• CVE-2026-40574: 0.21% estimated exploitation activity in the next 30 days; percentile 11.03 (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 An authorization bypass exists in OAuth2 Proxy as part of the emaildomain enforcement option. An attacker may be able to authenticate with an email claim such as attacker@evil.com@company.com and satisfy an allowed domain check for company.com, even though the claim is not a valid email address. The issue ONLY affects deployments that rely on emaildomain restrictions and accept email claim values from identity providers or claim mappings that do not strictly enforce normal email syntax. The practical risk ONLY exists in self-hosted or custom OIDC environments and federated setups where unexpected claim values can reach oauth2-proxy. Standard hosted providers that enforce valid email formatting ARE NOT effected. Patches Users should upgrade to v7.15.2 or later once available. Workarounds The most effective workaround is to ensure the configured identity provider cannot emit malformed or attacker-controlled email claim values.

Published by the source

15 Apr 2026, 19:23 UTC

Last modified by the source

27 Apr 2026, 16:15 UTC

Source last checked

26 Oct 2026, 15:19 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-c5c4-8r6x-56w3

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# Patch Next advisory brief: CVE-2026-40574

Advisory: OAuth2 Proxy has an Authorization Bypass in Email Domain Validation via Malformed Multi-@ Email Claims
IDs: CVE-2026-40574, GHSA-c5c4-8r6x-56w3
Record: https://patchnext.com/advisories/cve-2026-40574 (revision 1, source checked 26 Oct 2026, 15:19 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.8)
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 < 7.15.2; 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-c5c4-8r6x-56w3 (GitHub-reviewed advisory GHSA-c5c4-8r6x-56w3 lists affected ranges: Go github.com/oauth2-proxy/oauth2-proxy/v7 >=0 <7.15.2)

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