Network Security & Network Security Management
Cyber Security Operations Consulting is ushering in a new era of security operations and response with the industry’s first overall security program. This innovative, end-to-end computer network security operations and response architecture leverages advanced technology and dark web data detection technology to provide rapid and accurate security insights and response across endpoint, network, cloud and users.
Communications encompasses the breadth of digital data flows both within an organization and between external entities across network infrastructures. These flows now include data, voice, video, and all of their associated signaling protocols. Securing these information flows as they traverse Intranets, Extranets, and Internet requires effective network infrastructure management as well as controls, policies, and procedures. This chapter provides guidance in planning, developing, and implementing the most essential elements of a Communications Security strategy.
information that flows across internal networks and to/from the Internet, organization need to effectively manage their physical and logical network infrastructure. The protection of networked information assets requires policies, standards, and a sound network control strategy. If you are just getting started in this area of your security program, CyberSecOp can help you:
Develop policies and standards that support the:
Establishment of clear authority and accountability for network management.
Risk based segregation of groups of systems, users, and information systems
Authority to control, actively monitor, and log traffic traversing designated ingress and egress points.
Identify threats related to the communications environment.
Evaluate threat scenarios and methods of network attack (reconnaissance, exploitation, data exfiltration)
Identify the most critical systems, data, or equipment within the network. (see Asset Management)
Use routing and firewalls to define the network perimeter.
Use a border firewall and/or Intrusion Detection/Prevention devices to limit entry/exit of network traffic.
Define the “demilitarized zone” of the network where the public can access limited network resources, as well as public access points to the network such as open access ports and public WiFi.
Define restricted portions of the network for use by authorized staff and facility personnel; use identity and access management controls for users and systems on the network.
Define highly restricted portions of the network such as within data centers, communications facilities, or other highly restricted areas.
Establish information transfer policies and encryption standards that address varied needs for confidentiality, integrity, and non-repudiation of internal and external data exchanges.
Establishing Responsibility and Procedures for Network Management and Operations
Information flowing across networks cannot be secured without effective management of the physical and logical network infrastructure, including physical cabling, logical typologies, network devices, and network services. A centralized entity with appropriate responsibility and authority is generally the most effective way to ensure consistency and manageability across the Intranet and Extranets. In many organications, achieving a single point of responsibility and authority for all network infrastructure can be challenging. Management of network infrastructure includes network operations, which is a separate function from data center or information processing operations. Network security operations is often another distinct function, but must coordinate closely with network operations.
The large scale and high complexity of modern networks in organisation contributes to a challenging environment for security professionals and network administrators. The fundamental aspects of network services and protocols were not designed with information confidentiality in mind. Network Controls have been designed and implemented to compensate for this lack of security and continue to evolve as threat actors and their attack methods become more sophisticated.
Methods of Attack
Before determining which controls should be implemented and in which order, it is helpful to understand the common methods of attack. Note that a risk management approach is recommended to fully analyze all threats and responses. See the section Risk Management in this guide for more information.
The ultimate goal of attackers is to gain access to or modify data of value. Their targets are typically servers, workstations, or other computers connected to your organisation's networks, but they will make use of networks, other computers, people, or any other tool to achieve their objectives. Their attack strategies typically involve some form of reconnaissance, followed by exploitation – attempts to bypass or disable network or host security controls by exploiting vulnerabilities, and finally data modification or exfiltration. A Denial of Service (DoS) is a specific type of attack designed to disrupt operations or make networks and systems unavailable.
Reconnaissance – Attackers use reconnaissance to discover networks, hosts, or vulnerabilities. A variety of freely available tools are available that allow scanning or probing of systems accessible to the Internet. In targeting a specific organisation, an attacker need only know publicly available information such as the range of IP subnets used by the school. Scanning often involves discovering what TCP or UDP ports are active on the various hosts within the organisation's networks. Firewalls, IDS/IPS, network isolation, authentication, and logging are some of the tools network or security administrators use to limit or detect reconnaissance activities.
Exploitation – The protocols used across the Internet and within organisation Intranets and Extranets were designed for availability and openness rather than security and privacy. Attackers abuse and exploit the inherent lack of security of TCP/IP and the other various protocols and their associated network devices to their advantage. Their specific methods are numerous and varied, but can generally be categorized as follows:
- Sniffing – intercepting and examining network traffic
- Spoofing – impersonating a network host or user
- Man-in-the-Middle – covertly impersonating an intermediary host or network service such that the parties on either end of the connection are unaware that their communications are being captured and possibly altered
- Hijacking – taking over or re-routing one end of an otherwise valid communication between two parties
- Replay attacks – using intercepted communications or authentication interactions to falsely authenticate
- Password Cracking – using sophisticated or simple brute force attacks to guess weak passwords
- System or Application exploitation – once an attacker is in contact with a system at any of the application layer protocols such as FTP, Telnet, SSH, HTTP, HTTPS, SNMP, and others, weaknesses in the Operating System or the applications can be exploited to gain unauthorized access
Data Modification and Exfiltration – Once access to systems or data is gained, the data can be modified or copied (exfiltrated). While data owners might quickly know if data is modified, data exfiltration can take place in relative secrecy unless there are sufficient monitoring and controls in place to detect it. Most organisations have reasonable protections in place to prevent or detect external attacks, but are not as diligent in monitoring outbound traffic to detect confidential or sensitive data that is being copied by a successful attacker.
Like other types of security controls, network controls can be categorized into various types, depending on their primary function.
Preventive controls seek to stop or prevent attacks or intrusions before they occur. Firewalls, Intrusion Prevention Systems, Web Gateways, and physical Isolation of network cabling and devices are all examples of preventive controls.
Detective Controls seek to detect attacks or intrusions in progress or after (ideally very soon after!) they have already taken place. Intrusion Detection Systems, Log collection and review, Security Information and Event Management (SIEM) systems, AntiVirus software, and video surveillance in data centers and communications facilities are examples of detective controls.
Administrative controls direct users – employees, faculty, students, contractors, and partners – to follow specific procedures. Examples include policies against connecting rogue hubs, switches, or routers to the network, the use of network traffic sniffers, unauthorized network services, and procedures for provisioning network access accounts.
Technical controls often enforce administrative controls, but can also limit or prevent network activity/traffic, or isolate network segments or users to increase overall security. Examples include network access control, group policy objects, strong authentication, encryption, and Virtual Private Network (VPN) technology.
A sound network control strategy employs the concept of Defense In-Depth to provide optimal security. Firewalls at the network perimeter limit the traffic that is allowed in and out of the network. IDS/IPS devices detect and prevent traffic that is suspicious or known to be malicious. Internal network isolation limits the visibility of network traffic to devices and users by department or role. Access to wireless and wired networks are restricted to authenticated organisation faculty, staff, and students only. Strong passwords are enforced for all network computers. Computers run host-based firewalls and AntiVirus software. Certain sensitive network traffic is encrypted so that it cannot be intercepted. All of these controls are combined together to provide a layered or In-Depth defensive strategy.
Network Design and Architecture
Centralized management of organisation networks allows for a strategic network design and architecture that can be more readily optimized for performance, availability, and security. All endpoints should terminate to network switches to remove the possibility of internal network traffic sniffing by computers and users. Highly sensitive data and traffic such as for Data Centers or communications facilities should be isolated through virtual LAN (vLAN) technology and/or Firewalls. Highly unregulated traffic such as for student residence halls should also be isolated. For more information, see section 13.2 Network Isolation.
The architecture of the network should allow for the strategic placement of firewalls, demilitarized zones (DMZ's), and IDS/IPS devices such that all network traffic between the organisation Intranet and the Internet can be adequately controlled and monitored.
Perimeter controls must be strategically placed such that all network traffic flowing in and out of the organisation's internal networks, i.e. its Intranet, can be controlled and monitored. These controls are critical to network functionality and security and therefore must be fault-tolerant and have redundant backups available. In addition, they must be capable of processing the anticipated peak volume of network traffic. This is especially important for larger organisations with extremely high aggregate Internet bandwidth. Typical perimeter controls include:
- Routers – The border router is typically capable of allowing or denying connections, but it's primary purpose is to route traffic at the network border or DMZ
- Firewalls – firewalls (sometimes called border firewalls) block or limit traffic, typically by TCP/UDP port
- IDS/IPS – An Intrusion Detection System and/or Intrusion Prevention System adds an extra layer of protection, examining, limiting, or blocking traffic that was allowed through the border firewall, but is highly suspicious or known to be malicious
- Data Loss Prevention (DLP) – some DLP solutions inspect all network traffic to detect or block confidential data from leaving the Intranet
- "Next Generation" Firewalls – The term "NextGen" is a marketing term used by some vendors to imply a higher level of sophistication and thus a higher level of protection. While many of these products do perform as advertised, they are essentially serving the same or combined functions as firewall and IDS/IPS technology.
- Web Gateway – A secure web gateway does not necessarily sit at the perimeter, but does filter web-based traffic, providing more granular IDS/IPS functionality for web-based traffic or content
- Network Address Translation (NAT) – not strictly a security control, NAT limits the visibility of endpoints within the organisation Intranet from potential attackers on the Internet.
Note on encryption – while encryption is an effective control for data in transit, security administrators should also be aware that too much encryption of network traffic can severely limit many perimeter controls such as IDS/IPS, DLP, and Secure Web Gateways.
Many vendors are now providing cloud-based network protection, which can supplement or replace many of the on-premise perimeter or interior controls network and security administrators have used.
Isolation - Network segments or subnets within the organisation Intranet should be appropriately isolated according to the security requirements of the users and endpoints. Virtual LAN (vLAN) technology is the primary control used to isolate users and endpoints. Some typical segments might include Residence Halls, Research, PCIDSS, Data Center, Surveillance, Alarm Systems, and WiFi. See section 13.1.3 for more information on network isolation.
Endpoint Hardening - All network devices and endpoints should be hardened to reduce their attack surface. Hardening involves maintaining current patch levels, AntiVirus, host-based firewalls, host-based IDS/IPS, disabling unnecessary services, using strong passwords, and other protections as appropriate. Software whitelisting can also provide additional endpoint protection. Network and security administrators should not neglect printers, multi-function devices, and other network-attached devices which often have unsecure services opened up, such as FTP, Telnet, or SNMP.
Vulnerability Management - A Vulnerability Management System can help ensure that all endpoints on the network are adequately hardened. Vulnerability Management should ideally include web-based applications to reduce vulnerability to SQL-Injection, Cross-Site Scripting, and other web-based exploits.
Network Access Control (NAC) – Registering all endpoints before allowing connection to the network can prevent unauthorized devices from connecting as well as enforce security baselines. For instance, organisation IT Security Policies may state that all endpoints have automatic security updating enabled, authentication must be done via the central Active Directory domain, and AntiVirus and Firewall must be active. NAC can prevent systems which do not meet these requirements from accessing all or certain portions of the network.
WiFi Security Controls – WiFi should be protected and in most cases, isolated from all other internal networks, particularly when the organisation has chosen to make WiFi open-access. Open-access WiFi allows any computer within range to connect and therefore should be provided limited services such as Internet access only. WiFi that connects to more sensitive portions of the network should be limited to authorized users only. All WiFi should use WPA2 or stronger encryption. Note that enabling these levels of control across a large organisations can be costly and require sophisticated equipment.
Remote Access – remote access to internal or Intranet networks can be a high security risk if not properly planned and secured. While a Virtual Private Network (VPN) service is an excellent way to allow remote users to securely connect to your internal networks or Intranet, it provides no assurance that the connecting endpoint computer is itself secure. Security administrators should strongly consider enforcing Network Access Control for VPN connections or strictly limiting the use of VPN to selected trusted users. Outbound VPN can also introduce risk of opening up internal networks to potentially unsecure external networks. Many organisations chose to block outbound VPN at the firewall for this reason.
Other remote access tools and protocols need to be carefully controlled or limited. Remote Desktop Protocol (RDP) and Secure Shell (SSH) can introduce additional risk. RDP is best blocked at the firewall or provided through an RDP Gateway. While SSH is a secure protocol, the Linux and Unix systems that typically use SSH are often administered outside of the company directory service and can thus have weak passwords. External attackers routinely look for open SSH ports and attempt to use Rainbow tables or Brute Force to crack passwords.
Web-based services such as LogMeIn, VNC, GoToMyPC, etc. can also introduce risk of unauthorized remote access. Security administrators should carefully assess the risks associated with these services.
Back Doors – Remote Access protocols and services can create "back doors" of access into internal networks and should be carefully administered. Other back doors include analog modems, cellular services on smartphones and tablets, Bluetooth personal area networks, and removable media such as USB and CD/CDRW drives.
Encryption of certain network traffic is an essential network control. All confidential or sensitive information leaving the network should be encrypted with proven strong encryption algorithms. Authentication protocols that transmit passwords or encryption keys over the network should also be encrypted. Secure Sockets Layer (SSL) is a common encryption protocol used for web traffic.
Network Security Policies
A strong set of network security policies complements technical controls. While policies cannot always be technically enforced, users need to be aware of behaviors that are unacceptable by policy. Examples include:
- Use of strong passwords
- No sharing of user account credentials
- Users are not allowed to install and run illegal software, such as network sniffing/scanning or P2P File Sharing software
- All user accounts must be centrally managed and issued
- Prohibition of rogue switches, routers, hubs
- All network cabling and outlets must be installed by central network services
- Limited expectation of privacy
Security policies provide a means of enforcement in the event of known violations.
Log Management and Auditing
Routers, switches, IDS/IPS, firewalls, Directory Services controllers, and other network devices have a wealth of information about activity on the network. However, the massive amount of data they produce makes it difficult to adequately correlate and review for possible intrusions or perform forensic investigations. A Security Information and Event Management (SIEM) solution can greatly reduce the effort and expense involved and provide a much higher level of visibility for security. Network Access Control
All network controls should be routinely validated by an authorized external third party. The process is typically referred to as Penetration Testing (Pen Tests). A qualified Pen Tester can help ensure that the controls you have carefully implemented are working effectively. Many organisations are required to perform such testing on an annual or biennial basis.
Security of network services
Network services include Directory services, Domain Name Service (DNS), Dynamic Host Configuration Protocol (DHCP), authentication services, messaging/email, remote access, and others. These services have traditionally been provided on premise by network and/or security administrators. Today, many organisations are turning to outsourced cloud providers for many of these services.
On Premise Services
Most organization utilize some form of Directory Service, such as Microsoft Active Directory. Other essential services include DHCP, DNS, and remote access service such as VPN. Because these services operate at the network and IP layers of the OSI stack, and they perform essential functionality for all network hosts, they must be well-managed and secured. Only a very small number of network administrators should have administrative access to the underlying servers. These servers must also be hardened and kept up to date with security patches. Logging to an external aggregator or SIEM is also strongly recommended.
External Network Services
Highly available Internet connectivity has opened the door for organisations and other organizations to shift network and other application services to external cloud providers. While there are many reputable and very capable providers, it is nonetheless more difficult to hold an external entity accountable at the same levels possible with internal staff. organisations entering into agreements with cloud providers need to carefully review and negotiate the specific terms and conditions of these agreements. Service Level Agreements, Confidentiality Statements, and Privacy Policies are among the types of documents that must be carefully reviewed and updated. The default versions of these documents will typically be written in favor of the external provider rather than their customers. External service providers should be held to the same level of security controls as those that apply to internal services. organisations should write into their agreements language that specifies required security controls, limitation of access by provider's employees, confidentiality statements, the right of the organisation to audit security controls, and any other provisions that reduce risks of data disclosure, alteration, or loss.
Segregation in networks
One way to protect your confidential and/or critical systems is to segregate your networks along physical or logical lines. Using VLANs to separate your systems creates an additional layer of security between your regular network and your most sensitive systems. This method is often utilized in order to protect data centers, credit card processing systems covered by PCI DSS, SCADA systems, and other systems considered to be sensitive or mission critical.
In order to properly control access to your segregated networks, you should place a firewall or router at the perimeter of each network. That way, different networks can have different access control policies based on the sensitivity classification of the data that they create, transmit, and/or store. Special consideration should be given to wireless networks that allow anyone to connect for Internet access – if you offer an unsecured connection to your wireless network, you should take steps to ensure that wireless traffic is kept separate from the rest of your network or networks. Wireless users should not be able to access domain resources on your wired network without authenticating first, at least; most organizations now offer a secure wireless option (sometimes in addition to a separate, cordoned-off unsecure wireless option) to help maintain the confidentiality and integrity of their wired network.