**Root Cause Analysis:**
The CWE-476 vulnerability in the given code slice exists because it is accessing the `sp->do_auto_asconf` field without first checking if `sp` itself is NULL. If `sk` is NULL, then dereferencing it to access `sp` will result in a NULL pointer dereference, which is CWE-476.

This vulnerability can be fixed by adding a check for `sk` being NULL before accessing `sp`. For example:

```
if (sk != NULL) {
    struct sctp_sock *sp = sctp_sk(sk);
    // ... rest of the code ...
}
```