int mbedtls_ssl_handshake_server_step( mbedtls_ssl_context *ssl )
{
    int ret = 0;

    if( ssl->state == MBEDTLS_SSL_HANDSHAKE_OVER || ssl->handshake == NULL )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

    MBEDTLS_SSL_DEBUG_MSG( 2, ( "server state: %d", ssl->state ) );

    if( ( ret = mbedtls_ssl_flush_output( ssl ) ) != 0 )
        return( ret );

#if defined(MBEDTLS_SSL_PROTO_DTLS)
    if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM &&
        ssl->handshake->retransmit_state == MBEDTLS_SSL_RETRANS_SENDING )
    {
        if( ( ret = mbedtls_ssl_resend( ssl ) ) != 0 )
            return( ret );
    }
#endif

    switch( ssl->state )
    {
        case MBEDTLS_SSL_HELLO_REQUEST:
            ssl->state = MBEDTLS_SSL_CLIENT_HELLO;
            break;

        /*
         *  <==   ClientHello
         */
        case MBEDTLS_SSL_CLIENT_HELLO:
            ret = ssl_parse_client_hello( ssl );
            break;

#if defined(MBEDTLS_SSL_PROTO_DTLS)
        case MBEDTLS_SSL_SERVER_HELLO_VERIFY_REQUEST_SENT:
            return( MBEDTLS_ERR_SSL_HELLO_VERIFY_REQUIRED );
#endif

        /*
         *  ==>   ServerHello
         *        Certificate
         *      ( ServerKeyExchange  )
         *      ( CertificateRequest )
         *        ServerHelloDone
         */
        case MBEDTLS_SSL_SERVER_HELLO:
            ret = ssl_write_server_hello( ssl );
            break;

        case MBEDTLS_SSL_SERVER_CERTIFICATE:
            ret = mbedtls_ssl_write_certificate( ssl );
            break;

        case MBEDTLS_SSL_SERVER_KEY_EXCHANGE:
            ret = ssl_write_server_key_exchange( ssl );
            break;

        case MBEDTLS_SSL_CERTIFICATE_REQUEST:
            ret = ssl_write_certificate_request( ssl );
            break;

        case MBEDTLS_SSL_SERVER_HELLO_DONE:
            ret = ssl_write_server_hello_done( ssl );
            break;

        /*
         *  <== ( Certificate/Alert  )
         *        ClientKeyExchange
         *      ( CertificateVerify  )
         *        ChangeCipherSpec
         *        Finished
         */
        case MBEDTLS_SSL_CLIENT_CERTIFICATE:
            ret = mbedtls_ssl_parse_certificate( ssl );
            break;

        case MBEDTLS_SSL_CLIENT_KEY_EXCHANGE:
            ret = ssl_parse_client_key_exchange( ssl );
            break;

        case MBEDTLS_SSL_CERTIFICATE_VERIFY:
            ret = ssl_parse_certificate_verify( ssl );
            break;

        case MBEDTLS_SSL_CLIENT_CHANGE_CIPHER_SPEC:
            ret = mbedtls_ssl_parse_change_cipher_spec( ssl );
            break;

        case MBEDTLS_SSL_CLIENT_FINISHED:
            ret = mbedtls_ssl_parse_finished( ssl );
            break;

        /*
         *  ==> ( NewSessionTicket )
         *        ChangeCipherSpec
         *        Finished
         */
        case MBEDTLS_SSL_SERVER_CHANGE_CIPHER_SPEC:
#if defined(MBEDTLS_SSL_SESSION_TICKETS)
            if( ssl->handshake->new_session_ticket != 0 )
                ret = ssl_write_new_session_ticket( ssl );
            else
#endif
                ret = mbedtls_ssl_write_change_cipher_spec( ssl );
            break;

        case MBEDTLS_SSL_SERVER_FINISHED:
            ret = mbedtls_ssl_write_finished( ssl );
            break;

        case MBEDTLS_SSL_FLUSH_BUFFERS:
            MBEDTLS_SSL_DEBUG_MSG( 2, ( "handshake: done" ) );
            ssl->state = MBEDTLS_SSL_HANDSHAKE_WRAPUP;
            break;

        case MBEDTLS_SSL_HANDSHAKE_WRAPUP:
            mbedtls_ssl_handshake_wrapup( ssl );
            break;

        default:
            MBEDTLS_SSL_DEBUG_MSG( 1, ( "invalid state %d", ssl->state ) );
            return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    }

    return( ret );
}

The product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. This occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number.