Postgres uses High CPU - unable to find

Question

I'm having Postgres 9.6.4 in Ubuntu 17. After every few hours (say 6 hours or so), the OS CPU utilization becomes very high (upto 98% or more). I did the following:

# ps aux | grep postgres

Whenever the process/CPU is high, the above command shows postgres processes like this:

31928     1 ./x3665600000                0.2 99.8

The process name with x3665600000 always consumes near to 100% CPU.

When I checked the pg_stat_activity table, it shows SQL query like this:

select Fun310280 ('./x3665600000 &')
select Fun310280 ('./ps3657178651 &')

What is this function causing Postgres to use very high CPU?