Methods and apparatus for secure data modification using segmented hashing are disclosed. An intermediate device on a data path between a storage service and a client receives a modification request for a data segment of a data chunk of a storage object. The device generates a new chunk hash value for the chunk based on an original chunk hash value of the chunk, an original segment hash value of the segment to be modified, and a new segment hash value computed based on the modification. The device generates a modified version of the chunk based on the modification request, and uploads the modified version and the new chunk hash value to the storage service.