public int fibonacci ( int n ) { if ( n == 0 ) return 0 ; else if ( n == 1 ) return 1 ; else return fibonacci ( n - 1 ) + fibonacci ( n - 2 ); } Fibonacci function from Figure 1: Recursivefunction from Stack Overflow While Protobuf parsing is usually resilient against recursion attacks (using depth counters), Google forgot about this one code path during development.