Improper Input Validation

Summary

Open Policy Agent (OPA) is an open source, general-purpose policy engine. The Rego compiler provides a (deprecated) `WithUnsafeBuiltins` function, which allows users to provide a set of built-in functions that should be deemed unsafe and as such rejected by the compiler if encountered in the policy compilation stage. A bypass of this protection has been found, where the use of the `with` keyword to mock such a built-in function (a feature introduced in OPA v0.40.0), isn't taken into account by `WithUnsafeBuiltins`. Multiple conditions need to be met in order to create an adverse effect. This issue affects versions 0.40.x prior to 0.43.1. As a workaround, avoid using the `WithUnsafeBuiltins` function and use the `capabilities` feature instead.