OpenFGA is an authorization/permission engine. OpenFGA v1.5.7 and v1.5.8 are vulnerable to authorization bypass when calling Check API with a model that uses `but not` and `from` expressions and a userset. Users should downgrade to v1.5.6 as soon as possible. This downgrade is backward compatible. As of time of publication, a patch is not available but OpenFGA's maintainers are planning a patch for inclusion in a future release.