Techniques are provided for storing immutable snapshot copes in write once read many (WORM) storage. A snapshot of a volume may be stored into one or more objects formatted according to an object format. An expiry time may be assigned to the snapshot and the one or more objects based upon a creation time of the snapshot and a retention time. The one or more objects may be stored within a remote object store. The one or more objects are retained in an immutable state and cannot be deleted until expiration of the expiry time. In response to identifying an existing object within the remote object store comprising shared snapshot data referenced by the snapshot, an assigned expiry time of the existing object may be modified based upon the expiry time of the snapshot to create a modified expiry time for the existing object.