const struct Curl_handler *Curl_builtin_scheme(const char *scheme)
{
  const struct Curl_handler * const *pp;
  const struct Curl_handler *p;
  /* Scan protocol handler table and match against 'scheme'. The handler may
     be changed later when the protocol specific setup function is called. */
  for(pp = protocols; (p = *pp) != NULL; pp++)
    if(strcasecompare(p->scheme, scheme))
      /* Protocol found in table. Check if allowed */
      return p;
  return NULL; /* not found */
}

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.