Is this something new or ETERNALBLUE?
The fix disallows open on pipes with a name that starts with / : https://github.com/samba-team/samba/commit/02a76d86db0cbe79f...
status = smb_probe_module("rpc", pipename);
my guess is you can either pass in a pipename starting with / which will cause it to be treated absolutely or ../../ which will cause dlopen to do a relative lookup