C ++ dynamic segfault library

I am writing a network application in C ++ and I want to enable the creation of plugins, but I do not know what to do to protect my application from errors like segfault. For example: I have an interface:

class IPlugin{
public:
  IPlugin();
  virtual ~IPlugin();
  virtual void callPlugin() = 0;
}

And someone will write a dynamic library:

class Plugin : public IPlugin{
public:
  Plugin();
  virtual ~Plugin();
  virtual void callPlugin();
}

void Plugin::callPlugin(){
  int* a = NULL;
  *a = 5;
}

The call to this function in my application will end with the completion of everything. I know that I can use fork (), but the functions in the plugins will be short and will be used many times, so I think fork () is too slow. Any ideas?

PS. And sorry for my english.