All those big security issues aren't in the Java language, they are in the JVM running untrusted Java byte code. Not to say that situation isn't bad, but you can't compare it to C++ because nobody ever thought running untrusted C++ code without some other sandboxing was a good idea.

That aside, memory safety is great for security. Of course there are 1000 other things that are important, too, and so I'd trust a C program written by a security expert much more then the same program written by someone who thinks his program is secure because he used Java. But I'd feel even better if the security expert used a memory-safe language because I am certain that all C programs above a certain size are vulnerable to memory attacks.