GHSA-7hxc-f267-h5q7

The `ensurePathIsContained` function of the `Local` file system class is theoretically vulnerable to path traversal, although no exploitable scenario has been discovered.

When a file is read, an `Asset` object uses the `getFileStream` method of the `Volume` where the asset file is stored, which in turn uses the `getFileStream` method of the file system class used by that `Volume`. For the `Local` file system, this function returns a stream to a file on the local disk after verifying and creating the correct file path.

The file path is constructed by first validating the path and then adding a prefix to the validated and normalized path. The prefix is the path to the local directory that houses the particular volume. The order of operations matters here: first, a validation step, afterward a normalization step, and finally the construction of the resulting file path. This opens the possibility of a desanitization-style vulnerability, where the normalization invalidates the assumptions made by the validation or sanitization that preceded it.

## Impact

The issue is not directly exploitable, but for hardening, a fix is recommended regardless.