Depends on implementation. CPython may have problems due to C bugs. Java is self-bootstrapping, though, and has no relation to C except for interfacing with external programs using C calling conventions. In this case problems are not hidden, they are truly not existing, except for problems introduced by other programs you interface with - but not your code.

You're quite wrong regarding Java. Much of its standard library is implemented in C and C++, and there have been frequent security vulnerabilities found in the language that are a result of buffer overflows or similar memory corruption bugs within the underlying C/C++ implementation.

There are many, but here's one such example from last year: http://osvdb.org/show/osvdb/94336