Vulnerability · Published Nov 10, 2025 · Assigned by GitHub_M
CVE-2025-64484OAuth2-Proxy vulnerable to header smuggling via underscore, leading to potential privilege escalation
High 8.5
In plain English
A high-severity security flaw 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 0.7% (higher than 52% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
OAuth2-Proxy is an open-source tool that can act as either a standalone reverse proxy or a middleware component integrated into existing reverse proxy or load balancer setups. In versions prior to 7.13.0, all deployments of OAuth2 Proxy in front of applications that normalize underscores to dashes in HTTP headers (e.g., WSGI-based frameworks such as Django, Flask, FastAPI, and PHP applications). Authenticated users can inject underscore variants of X-Forwarded-* headers that bypass the proxy’s filtering logic, potentially escalating privileges in the upstream app. OAuth2 Proxy authentication/authorization itself is not compromised. The problem has been patched with v7.13.0. By default all specified headers will now be normalized, meaning that both capitalization and the use of underscores (_) versus dashes (-) will be ignored when matching headers to be stripped. For example, both `X-Forwarded-For` and `X_Forwarded-for` will now be treated as equivalent and stripped away. For those who have a rational that requires keeping a similar looking header and not stripping it, the maintainers introduced a new configuration field for Headers managed through the AlphaConfig called `InsecureSkipHeaderNormalization`. As a workaround, ensure filtering and processing logic in upstream services don't treat underscores and hyphens in Headers the same way.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Go | github.com/oauth2-proxy/oauth2-proxy | no fix listed | GO-2025-4113 |
| Go | github.com/oauth2-proxy/oauth2-proxy/v7 | 7.13.0 | GHSA-vjrc-mh2v-45x6 |
| Go | github.com/oauth2-proxy/oauth2-proxy/v7 | 7.13.0 | GO-2025-4113 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| oauth2-proxy | oauth2-proxy | < 7.13.0 |
Weakness: CWE-644 · Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:L/A:N
References
- https://github.com/oauth2-proxy/oauth2-proxy/security/advisories/GHSA-vjrc-mh2v-45x6 x_refsource_CONFIRM
- https://datatracker.ietf.org/doc/html/rfc2616#section-4.2 x_refsource_MISC
- https://datatracker.ietf.org/doc/html/rfc822#section-3.2 x_refsource_MISC
- https://github.security.telekom.com/2020/05/smuggling-http-headers-through-reverse-proxies.html x_refsource_MISC
- https://www.uptimia.com/questions/why-are-http-headers-with-underscores-dropped-by-nginx x_refsource_MISC