Summary

faker.helpers.fake can be tricked into arbritary code execution.

Details

fakeEval.resolveProperty resolves properties on functions itself instead of resolving the nested function first. This can be addressed by recursively calling resolveProperty instead of accessing the property after one iteration.

PoC

Go to https://fakerjs.dev/ Open Browser console and run

ts await enableFaker(); // or import faker faker.rawDefinitions.test = (() => () => {}); // Any function that returns a function faker.helpers.fake({{test.constructor(alert('PowerLevel: Eval'))}});

Impact

The Fake method claims:

It is also NOT possible to use any non-faker methods or plain javascript in such patterns.

Which is objectively false, since any global gets fully accessible in the fake string.