Affected versions of borsh cause undefined behavior when zero-sized-types (ZST) are parsed and the Copy/Clone traits are not implemented/derived. For instance if 1000 instances of a ZST are deserialized, and the ZST is not copy (this can be achieved through a singleton), then accessing/writing to deserialized data will cause a segmentation fault. There is currently no way for borsh to read data without also providing a Rust type. Therefore, if not ZST are used for serialization, then you are not affected by this issue.