CVE-2021-21291 Explained : Impact and Mitigation

OAuth2 Proxy is an open-source reverse proxy and static file server that provides authentication using Providers (Google, GitHub, and others) to validate accounts by email, domain, or group. In OAuth2 Proxy before version 7.0.0, a vulnerability in the whitelist domain feature could allow unintended redirects. This CVE has a base score of 4.7, indicating a medium severity.

Understanding CVE-2021-21291

This CVE highlights a security issue in OAuth2 Proxy related to the handling of whitelisted domains.

What is CVE-2021-21291?

The vulnerability in OAuth2 Proxy versions prior to 7.0.0 allowed domains with similar endings to be erroneously allowed for redirection, impacting the security of whitelisted domains.

The Impact of CVE-2021-21291

The impact of this CVE is medium, with a CVSS base score of 4.7. If exploited, it could lead to potentially unintended redirects to untrusted sites.

Technical Details of CVE-2021-21291

This section delves into the specifics of the vulnerability.

Vulnerability Description

The vulnerability allowed domains with similar endings to the intended whitelisted domain to be considered valid, potentially leading to unauthorized redirects.

Affected Systems and Versions

OAuth2 Proxy versions prior to 7.0.0 are affected by this vulnerability.

Exploitation Mechanism

Attackers could exploit the vulnerability by crafting URLs with domains that mimic the intended whitelisted domains.

Mitigation and Prevention

To mitigate the risks associated with CVE-2021-21291, immediate steps and long-term security practices can be implemented.

Immediate Steps to Take

Disable the whitelist domain feature in affected OAuth2 Proxy instances and consider running separate instances for each subdomain.

Long-Term Security Practices

Regularly update OAuth2 Proxy to the latest version to ensure all security patches are applied promptly.

Patching and Updates

Update to OAuth2 Proxy version 7.0.0 or newer to address the vulnerability and prevent unintended redirects.