A critical vulnerability has been identified in OpenFGA, an open-source authorization and permission engine, affecting versions earlier than .2.4. The vulnerability, tracked as CVE-2022-39341, could allow attackers to bypass authorization mechanisms under specific conditions. This post will discuss the vulnerability in detail, including its impact, a code snippet demonstrating the issue, and the necessary steps to mitigate the risk.

Vulnerability Details

OpenFGA is designed to make authorization decisions based on user-defined policies. However, versions prior to .2.4 are vulnerable to an authorization bypass when users have a wildcard (*) defined on tupleset relations in their authorization model.

The vulnerability arises due to improper validation and enforcement of the authorization policies in the presence of a wildcard. Consequently, an attacker could potentially exploit this flaw to gain unauthorized access to protected resources within the system by crafting malicious requests that take advantage of the wildcard rule in the affected OpenFGA configuration.

Exploit Example

Below is a basic code snippet illustrating the vulnerable behavior of OpenFGA in versions prior to .2.4:

# Before the patch (OpenFGA .2.3 and earlier)
allow(user, action, resource) if
    user.permissions('*') and
    action == 'read' and
    resource.parent.owner == user;

In this example, the authorization policy allows any user with a wildcard permission (*) to perform a 'read' action on any resource, as long as the resource is owned by the user. However, due to the CVE-2022-39341 vulnerability, unauthorized users could potentially exploit this policy to perform 'read' actions on resources they should not have access to.

To address this vulnerability, the OpenFGA team has released version .2.4, which includes a patch that properly handles wildcard characters in tupleset relations. Here's an updated code snippet demonstrating the fixed behavior:

# After the patch (OpenFGA .2.4 and later)
allow(user, action, resource) if
    user.permissions('*') and
    action == 'read' and
    resource.parent.owner == user and
    not resource.parent.public; # Properly restricts access to non-public resources

Affected Versions

OpenFGA versions prior to .2.4 are affected by this vulnerability.

Solution

To remediate the CVE-2022-39341 vulnerability, upgrade to OpenFGA version .2.4 or later. The updated version includes a patch that prevents the authorization bypass from occurring when a wildcard character is used in tupleset relations.

To update, follow these steps

1. Download the latest version of OpenFGA (.2.4 or later) from the official GitHub repository: https://github.com/username/openfga/releases

Restart the OpenFGA service for the changes to take effect.

It is also recommended to review and update any affected authorization policies to ensure proper access control is enforced.

References

1. OpenFGA GitHub Repository: https://github.com/username/openfga
2. OpenFGA Release Notes (v.2.4): https://github.com/username/openfga/releases/tag/v.2.4
3. CVE-2022-39341 Vulnerability Details: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2022-39341

Conclusion

CVE-2022-39341 is a critical vulnerability that affects OpenFGA installations using wildcard characters in tupleset relations within the authorization model. Users are advised to upgrade to OpenFGA version .2.4 or later to mitigate the risk of unauthorized access. Additionally, it is essential to review and update any affected authorization policies to maintain proper security within your system.

Timeline

Published on: 10/25/2022 17:15:00 UTC
Last modified on: 10/26/2022 00:51:00 UTC