This code will cause InDesign 17.1 to hang and consume all available resources until the computer eventually runs out of both real and virtual memory and then crashes.

app.findGrepPreferences = app.changeGrepPreferences = null;
app.findChangeGrepOptions.properties = { includeMasterPages: true, kanaSensitive: true, widthSensitive: true };
app.findGrepPreferences = null;
app.findGrepPreferences.findWhat = '^(.*)$';

var found = app.documents[0].changeObject.findGrep();

If the runaway app is terminated using Task Manager (Windows 10), a stack of message boxes appear with the following message:
Unable to terminate process
The operation could not be completed
The operation is not valid for this process