static void append_cs_return(cs_entry * ptr)
{
    unsigned short cr;
    int i;
    byte *p, *q, *data, *new_data;
    /*tex Decrypt the cs data to |t1_buf_array|, append |CS_RETURN|. */
    p = (byte *) t1_buf_array;
    data = ptr->data + 4;
    cr = 4330;
    for (i = 0; i < ptr->cslen; i++)
        *p++ = cs_getchar();
    *p = CS_RETURN;
    /*tex Encrypt the new cs data to |new_data|. */
    new_data = xtalloc((unsigned) (ptr->len + 1), byte);
    memcpy(new_data, ptr->data, 4);
    p = new_data + 4;
    q = (byte *) t1_buf_array;
    cr = 4330;
    for (i = 0; i < ptr->cslen + 1; i++)
        *p++ = cencrypt(*q++, &cr);
    memcpy(p, ptr->data + 4 + ptr->cslen, (size_t) (ptr->len - ptr->cslen - 4));
    /*tex Update |*ptr|. */
    xfree(ptr->data);
    ptr->data = new_data;
    ptr->len++;
    ptr->cslen++;
}

The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.