CVE-2020-11053: Open Redirect in OAuth2 Proxy

Severity: medium (CVSS 6.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.8% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2020-05-07 · updated 2026-06-17
Weakness: CWE-601

Description

In OAuth2 Proxy before 5.1.1, there is an open redirect vulnerability. 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. However, by crafting a redirect URL with HTML encoded whitespace characters the validation could be bypassed and allow a redirect to any URL provided. This has been patched in 5.1.1.

Affected products

oauth2-proxy: before 5.1.1 — fixed in 5.1.1

How to fix

Upgrade to a fixed version: oauth2-proxy 5.1.1. Check the vendor advisory for mitigations.

References

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