It's sexual assault in the first degree.
Using the excuse you are looking for contraband doesn't change the law. There are other ways that don't involve the penetration of a persons anus with ones finger to detect the presence of contraband, like an x ray for instance. There is simply no excuse for this and anyone who says there is is a sick mother*&&**
For some odd reason police seem to be totally exempt from many laws without any provisions in said law to allow for it.