CVE-2021-21291

What it is

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, for users that use the whitelist domain feature, a domain that ended in a similar way to the intended domain could have been allowed as a redirect. For example, if a whitelist domain was configured for ".example.com", the intention is that subdomains of example.com are allowed. Instead, "example.com" and "badexample.com" could also match. This is fixed in version 7.0.0 onwards. As a workaround, one can disable the whitelist domain feature and run separate OAuth2 Proxy instances for each subdomain.

At a glance

Exploitability

Can be exploited over the network without logging in, but needs a user to act. Limited direct impact.

Exploit odds

1.6% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2021-02-02 19:15 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-06-17 03:35 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 1.6% in the next 30 days (EPSS).
• Severity: 4.7 MEDIUM (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2021-02-02 19:15 UTC

Last modified

2026-06-17 03:35 UTC

Exploit probability

1.6% · EPSS, next 30 days

Weakness

CWE-601

Record status

Modified

Affected

• oauth2 Proxy Project oauth2 Proxy < 7.0.0

Attack profile CVSS 3.1 · 4.7

Attack vector

Network

Complexity

High

Privileges needed

None

User interaction

Required

Scope

Changed

Confidentiality

Low

Integrity

Low

Availability

None

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2021-21291.md and follow it. Check whether this project is affected by CVE-2021-21291. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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