CVE-2020-4037 Open Redirect in OAuth2 Proxy
Attackers can exploit insufficient validation of redirect URLs in OAuth2 Proxy to send authenticated users to malicious sites.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2020-4037?
CVE-2020-4037 is a medium-severity vulnerability in OAuth2 Proxy, published on 29 Jun 2020. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
In OAuth2 Proxy from version 5.1.1 and less than version 6.0.0, users can provide a redirect address for the proxy to send the authenticated user to at the end of the authentication flow. This is expected to be the original URL that the user was trying to access. This redirect URL is checked within the proxy and validated before redirecting the user to prevent malicious actors providing redirects to potentially harmful sites. This has been fixed in version 6.0.0.
Weakness: CWE-601
Which versions are affected by CVE-2020-4037?
3 open source packages ship an affected version, including github.com/oauth2-proxy/oauth2-proxy and oauth2-proxy. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
github.com/oauth2-proxy/oauth2-proxy Go | From 5.1.1 | 6.0.0 |
github.com/oauth2-proxy/oauth2-proxy Go | From 5.1.1 | 6.0.0 |
oauth2-proxy Bitnami | From 5.1.1 | 6.0.0 |
Products include Oauth2 Proxy Project Oauth2 Proxy.
How do I fix CVE-2020-4037?
Upgrade github.com/oauth2-proxy/oauth2-proxy to 6.0.0 or later.
Is CVE-2020-4037 being exploited?
There is no known exploitation of CVE-2020-4037 in the wild and no public exploit code.
Other vulnerabilities in OAuth2 Proxy
- CVE-2026-40575 OAuth2 Proxy has an Authentication Bypass via X-Forwarded-Uri Header Spoofing
- CVE-2026-34457 OAuth2 Proxy: Health Check User-Agent Matching Bypasses Authentication in auth_request Mode
- CVE-2025-54576 OAuth2-Proxy has authentication bypass in oauth2-proxy skip_auth_routes due to Query Parameter inclusion
- CVE-2017-1000069 Cross-site Request Forgery (CSRF)
- CVE-2026-41059 OAuth2 Proxy has an Authentication Bypass via Fragment Confusion in skip_auth_routes and skip_auth_regex
Sources
Also known as BIT-oauth2-proxy-2020-4037, GHSA-5m6c-jp6f-2vcv.