If the definition of a recursive CTE r is used in the WITH clause without RECURSIVE and this clause is part of the query expression that defines another CTE then the server falls into an infinite recursion calling With_element::clone_parsed_spec() again and again. Ultimately it causes a crash of the server.
Here's a test case that causes such crash:

create table t1 (a int);

insert into t1 values (5), (7);

with cte_e as (

   with cte_r as ( 

      select a from t1   union  select a+1 as a from cte_r r where a < 10

   )   select * from cte_r 

) select * from cte_e;

It should be noted that the definition of cte_r is not considered as the definition of a recursive CTE. Rather it is considered as the definition of a non-recursive CTE referencing the base table or view with the name cte_r. This is because the WITH clause containing this definition lacks the keyword RECURSIVE.
So the expected reaction of the server should be similar to this:

MariaDB [test]>    with cte_r as ( 

    ->       select a from t1   union  select a+1 as a from cte_r r where a < 10

    ->    )   select * from cte_r 

    -> ;

ERROR 1146 (42S02): Table 'test.cte_r' doesn't exist