Postgresql regex replace numbers to asterisks

I use Postgresql and need to replace numbers to asterisk at database layer. Howerver I’m new to learn regex and seems to be hard to do this with my current knowledge.

I will have in my database 16 numbers varchar and I need to replace middle numbers with asterisk.

Example.
123467812345678 -> 12**********5678

Could someone tell me how regex for this should look like in postgresql ?
Thanks in advance

>Solution :

Thanks to @Wiktor Stribiżew:

SELECT regexp_replace('123467812345678', '(?<=..).(?=....)', '*','g');