Struggling to find a way to extract data between 2 strings

[sourabhkrishna]

Sample Data:

**** GUID1 START **** data1 data2 **** GUID1 END ****

**** GUID2 START **** data1 data2 data3 **** GUID2 END ****

**** GUID3 START **** data1 data2

**** GUID4 START **** data1 data2 data3 data4 **** GUID4 END ****

The above is how my input data in txt file format is generated. How do I extract data between start and end Guids and ignore all guid that do not have an end mentioned in the data.