Root Cause Analysis: Looking at the given vulnerable code line and its context, the CWE-787 (Out-of-bounds Write) vulnerability exists in the code because the `realloc` function is used to allocate memory for the `p` pointer without checking if the resulting pointer is `NULL`. If the `realloc` function fails to allocate memory, then the `p` pointer will be `NULL`, and accessing the memory at the `p` pointer will result in an out-of-bounds write vulnerability, which is CWE-787.