CVE-2020-15234 Redirect URL matching ignores character casing

Medium 6.1 Published 2 Oct 2020 Updated 4 Aug 2024

An attacker can bypass redirect URL validation by exploiting case-insensitive matching, potentially redirecting users to malicious sites during OAuth2 flows.

Exploited in the wild: Not known
Login needed: An administrator
Attackable: Over the internet
Victim action needed: A user has to click or open something
Fix: Available

What is CVE-2020-15234?

CVE-2020-15234 is a medium-severity vulnerability in ory fosite, published on 2 Oct 2020. An attacker needs administrator access to exploit it, and only if a user opens a file or follows a link.

Official description

ORY Fosite is a security first OAuth2 & OpenID Connect framework for Go. In Fosite before version 0.34.1, the OAuth 2.0 Client's registered redirect URLs and the redirect URL provided at the OAuth2 Authorization Endpoint where compared using strings.ToLower while they should have been compared with a simple string match. This allows an attacker to register a client with allowed redirect URL https://example.com/callback. Then perform an OAuth2 flow and requesting redirect URL https://example.com/CALLBACK. Instead of an error (invalid redirect URL), the browser is redirected to https://example.com/CALLBACK with a potentially successful OAuth2 response, depending on the state of the overall OAuth2 flow (the user might still deny the request for example). This vulnerability has been patched in ORY Fosite v0.34.1.

Weakness: CWE-178, CWE-601, CWE-20

Which versions are affected by CVE-2020-15234?

2 open source packages ship an affected version, including github.com/ory/fosite. It affects 1 product.

Package	Affected	Fixed in
`github.com/ory/fosite` Go	All versions	`0.34.1`
`github.com/ory/fosite` Go	All versions	`0.34.1`

Products include Ory Fosite.

How do I fix CVE-2020-15234?

Upgrade github.com/ory/fosite to 0.34.1 or later.

Is CVE-2020-15234 being exploited?

There is no known exploitation of CVE-2020-15234 in the wild and no public exploit code.

Sources

Also known as GHSA-grfp-q2mm-hfp6.