A: Root Cause Analysis: Looking at the given vulnerable code line and its context, the CWE-787 (Out-of-bounds Write) vulnerability exists because the `realloc` function is used to reallocate memory for the `*data` pointer without checking if the reallocation was successful. If the `realloc` operation fails, the `*data` pointer will be set to `NULL`, and accessing it will result in a use-after-free vulnerability, which is CWE-787.