An unsafe deserialization issue exists in the WebDataset reader. An attacker can achieve remote code execution by providing a malicious tar archive to the `read webdataset()` function. The ` default decoder()` function in webdataset datasource.py unconditionally calls `pickle.loads()` on tar entries with .pkl or .pickle extensions and `torch.load()` with `weights only=False` on .pt or .pth entries. This results in the execution of arbitrary code within Ray remote workers on every worker that processes the malicious archive. Deserialization is the process of converting a data format back into an object, which becomes unsafe when untrusted data is processed without validation.