CVE-2020-15233: OAuth2 Redirect URL validity does not respect query parameters and character casing for loopback addresses in github.com/ory/fosite
Summary
CVE-2020-15233: Impact fosite#400 (released as v0.30.2) introduced a new feature for handling redirect URLs pointing to loopback interfaces (rfc8252#section-7.3). Affects github.com/ory/fosite versions >= 0.30.3, < 0.34.1. Fixed in 0.34.1. How to fix ↓
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Background
github.com/ory/fosite is a Go package that provides a secure and flexible OAuth2 server implementation. It allows developers to easily integrate OAuth2 authentication and authorization into their applications. The package is widely used in various Go projects and provides essential functionality for handling OAuth2 flows.
Vulnerability Detail
The vulnerability (CVE-2020-15233) in github.com/ory/fosite affects the handling of redirect URLs pointing to loopback interfaces. The issue arises from a new feature introduced in version 0.30.2, which fails to respect query parameters and character casing for loopback addresses. This means that an attacker who has control over the loopback interface can manipulate the redirect URL and potentially bypass security measures. For example, an attacker could register a client with a redirect URL of 'http://127.0.0.1/callback' and include additional query parameters. When the OAuth2 flow is performed and the redirect URL is requested, the browser is redirected to the manipulated URL without any error, potentially leading to a successful OAuth2 response. This vulnerability only affects scenarios where the attacker has control over the loopback interface where the OAuth2 flow is being executed.
How To Fix
Latest published version: v0.49.0 as of 23 Oct 2026
go get github.com/ory/fosite@v0.49.0Upgrading to it may include breaking changes; the version below is the minimum fixed release for this vulnerability.
If you need the minimum change
0.34.1
This is the first release that contains the fix.
go get github.com/ory/fosite@v0.34.1Tip — Not sure which version your app runs? Vulert can match this fix to it. Scan free →
Workaround
There is no known workaround for this vulnerability. It is recommended to upgrade to the fixed version of github.com/ory/fosite as soon as possible.
Conclusion
The vulnerability in github.com/ory/fosite (CVE-2020-15233) allows for the manipulation of redirect URLs pointing to loopback interfaces, potentially bypassing security measures. Developers should upgrade to version 0.34.1 or later to fix this vulnerability. It is important to apply the fix to prevent any potential exploitation. For further support on vulnerability remediation, you can reach out to DevNack.com.
See every vulnerability recorded for github.com/ory/fosite →
FAQ
The vulnerability allows an attacker to manipulate redirect URLs pointing to loopback interfaces, potentially bypassing security measures and obtaining unauthorized access to OAuth2 resources.
No, this vulnerability only affects loopback interfaces such as 'localhost', '127.0.0.1', and '[::1]'. Other loopback interfaces are not affected.
No, this vulnerability requires the attacker to have control over the loopback interface where the OAuth2 flow is being executed. Remote exploitation is not possible.
There are no known instances of this vulnerability being exploited in the wild. However, it is still important to apply the fix to prevent any potential exploitation.
If you suspect that your application is affected by this vulnerability, you can use Vulert's playground (https://vulert.com/scanner) to check if your application is vulnerable. Vulert monitors and alerts in real-time for open-source vulnerabilities, providing valuable insights without requiring access to the code or installation.
References
Related vulnerabilities
Recent vulnerabilities recorded for github.com/ory/fosite.
