Feast before version 0.63.0 contains a critical unsafe deserialization vulnerability. The vulnerability occurs in the registry server component where the user_defined_function.body field of an OnDemandFeatureView specification is base64 decoded and deserialized using dill.loads() prior to any authorization checks. An attacker can exploit this by sending a crafted gRPC request embedding a malicious serialized Python object with an arbitrary __reduce__ method, enabling remote code execution with the privileges of the feast service account. This vulnerability requires no authentication or user interaction and has a CVSS 4.0 score of 9.3, indicating high impact on confidentiality, integrity, and availability.

Successful exploitation allows unauthenticated remote attackers to execute arbitrary operating system commands on the feast registry server with the privileges of the feast service account. This can lead to full compromise of the affected system, including data theft, service disruption, or further lateral movement within the environment.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until an official fix is available, restrict network access to the feast registry server to trusted users only and monitor for suspicious gRPC requests. Avoid deploying vulnerable versions in untrusted environments.