Select specific string with line break

Hello all,

I would like to only select "CN=*whatever*" from the line below

> C:\test\temp_523410.txt:18:Subject:
  C:\test\temp_523410.txt:19:    CN=domain.local
  C:\test\temp_523410.txt:20:    O=Test Organization
  C:\test\temp_523410.txt:21:    L=City