Vulnerability · Published Apr 21, 2026 · Assigned by GitHub_M
CVE-2026-40574OAuth2 Proxy has an Authorization Bypass in Email Domain Validation via Malformed Multi-@ Email Claims
Medium 6.8
In plain English
A medium-severity incorrect authorization in oauth2-proxy from oauth2-proxy. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 11% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Go | github.com/oauth2-proxy/oauth2-proxy | no fix listed | GO-2026-5314 |
| Go | github.com/oauth2-proxy/oauth2-proxy/v7 | 7.15.2 | GHSA-c5c4-8r6x-56w3 |
| Go | github.com/oauth2-proxy/oauth2-proxy/v7 | 7.15.2 | GO-2026-5314 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| oauth2-proxy | oauth2-proxy | < 7.15.2 |
Weakness: CWE-863 · Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N