CAMediaTimingFunctionBuiltin is a class in QuartzCore. Its initWithCoder: method
reads an Int "index" then passes that to builtin_function

  mov     ebx, edi <-- controlled unsigned int
  mov     r14d, ebx
  lea     r15, __ZL9functions_0 ; functions
  mov     rax, [r15+r14*8]

if rax is non-null it's returned as an objective-c object pointer and the objective-c retain
selector is sent to it.

Serialized poc in attached file with an index of 12345678.

tested on MacOS 10.12.3 (16D32)
 

functionbuiltin.zip 1.2 KB Download