Root Cause Analysis: Looking at the given vulnerable code line and its context, the CWE-476 (NULL Pointer Dereference) vulnerability exists in the code because the `addr` pointer is being dereferenced without first checking if it is NULL. If `hash_lookup` at line 6 fails to find a valid address and returns NULL, dereferencing `addr` at line 7 will result in a NULL pointer dereference vulnerability, which is CWE-476.