From version X4 (14) on, the CDR file is a ZIP-compressed directory of several files, among them XML-files and the RIFF-structured riffdata.cdr with the familiar version signature in versions X4 (CDREvrsn) and X5 (CDRFvrsn), and a root.dat with Corel Draw X6, where the bytes 9 to 15 look slightly different -- "CDRGfver" in a file created with X6. "F" was the last valid hex digit, and the "fver" now indicates that the letter before does no longer stand for a hex digit.
There is no publicly available CDR file format specification.