| Internet Engineering Task Force | T. Mizrahi |
| Internet-Draft | MARVELL |
| Intended status: Informational | E. Grossman, Ed. |
| Expires: September 14, 2017 | DOLBY |
| A. Hacker | |
| MISTIQ | |
| S. Das | |
| Applied Communication Sciences | |
| J. Dowdell | |
| Airbus Defence and Space | |
| March 13, 2017 |
Deterministic Networking (DetNet) Security Considerations
draft-sdt-detnet-security-00
A deterministic network is one that can carry data flows for real-time applications with extremely low data loss rates and bounded latency. Deterministic networks have been successfully deployed in real-time operational technology (OT) applications for some years (for example [ARINC664P7]). However, such networks are typically isolated from external access, and thus the security threat from external attackers is low. IETF Deterministic Networking (DetNet) specifies a set of technologies that enable creation of deterministic networks on IP-based networks of potentially wide area (on the scale of a corporate network) potentially bringing the OT network into contact with Information Technology (IT) traffic and security threats that lie outside of a tightly controlled and bounded area (such as the internals of an aircraft). These DetNet technologies have not previously been deployed together on a wide area IP-based network, and thus can present security considerations that may be new to IP-based wide area network designers. This draft, intended for use by DetNet network designers, provides insight into these security considerations. In addition, this draft collects all security-related statements from the various DetNet drafts (Architecture, Use Cases, etc) into a single location Section 4.
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Security is of particularly high importance in DetNet networks because many of the use cases which are enabled by DetNet [I-D.ietf-detnet-use-cases] include control of physical devices (power grid components, industrial controls, building controls) which can have high operational costs for failure, and present potentially attractive targets for cyber-attackers.
This situation is even more acute given that one of the goals of DetNet is to provide a "converged network", i.e. one that includes both IT traffic and OT traffic, thus exposing potentially sensitive OT devices to attack in ways that were not previously common (usually because they were under a separate control system or othewise isolated from the IT network). Security considerations for OT networks is not a new area, and there are many OT networks today that are connected to wide area networks or the Internet; this draft focuses on the issues that are specific to the DetNet technologies and use cases.
This initial version of this draft consists of a threat model and analysis, and in the future will be expanded to include mitigation strategies.
This draft also provides context for the DetNet security considerations by collecting into one place Section 4 the various remarks about security from the various DetNet drafts (Use Cases, Architecture, etc). This text is duplicated here primarily because the DetNet working group has elected not to produce a Requirements draft and thus collectively these statements are as close as we have to "DetNet Security Requirements".
The DetNet technologies include ways to:
IT Information technology (the application of computers to store, study, retrieve, transmit, and manipulate dataor information, often in the context of a business or other enterprise - Wikipedia).
OT Operational Technology (the hardware and software dedicated to detecting or causing changes in physical processes through direct monitoring and/or control of physical devices such as valves, pumps, etc. - Wikipedia)
MITM Man in the Middle
SN Sequence Number
STRIDE Addresses risk and severity associated with threat categories: Spoofing identity, Tampering with data, Repudiation, Information disclosure, Denial of service, Elevation of privilege.
DREAD Compares and prioritizes risk represented by these threat categories: Damage potential, Reproducibility, Exploitability, how many Affected users, Discoverablility.
PTP Precision Time Protocol [IEEE1588]
This section presents a threat model, and analyzes the possible threats in a DetNet-enabled network.
We distinguish control plane threats from data plane threats. The attack surface may be the same, but the types of attacks are different. For example, a delay attack is more relevant to data plane than to control plane. There is also a difference in terms of security solutions: the way you secure the data plane is often different than the way you secure the control plane.
The threat model used in this memo is based on the threat model of Section 3.1 of [RFC7384]. This model is briefly presented in this subsection.
The model classifies attackers based on two criteria:
An attacker can maliciously delay DetNet data flow traffic. By delaying the traffic, the attacker can compromise the service of applications that are sensitive to high delays or to high delay variation.
An attacker can modify some header fields of en route packets in a way that causes the DetNet flow identification mechanisms to misclassify the flow. Alternatively, the attacker can inject traffic that is tailored to appear as if it belongs to a legitimate DetNet flow. The potential consequence is that the DetNet flow resource allocation cannot guarantee the performance that is expected when the flow identification works correctly.
Note that in some cases there may be an explicit DetNet header, but in some cases the flow identification may be based on fields from the L3/L4 headers. If L3/L4 headers are involved, for purposes of this draft we assume they are encrypted and/or integrity-protected from external attackers.
An attacker can inject traffic, consuming network device resources, thereby affecting DetNet flows. This can be performed using non-DetNet traffic that affects DetNet traffic, or by using DetNet traffic from one DetNet flow that affects traffic from different DetNet flows.
Redundancy is intended to increase the robustness and survivability of DetNet flows, and replication over multiple paths can potentially mitigate an attack that is limited to a single path. However, the fact that packets are replicated over multiple paths increases the attack surface of the network, i.e., there are more points in the network that may be subject to attacks.
An attacker can manipulate the replication-related header fields (R-TAG). This capability opens the door for various types of attacks. For example:
An attacker can maliciously change, add, or remove a path, thereby affecting the corresponding DetNet flows that use the path.
One of the possible consequences of a path manipulation attack is an increased attack surface. Thus, when the attack described in the previous subsection is implemented, it may increase the potential of other attacks to be performed.
An attacker can maliciously modify en route control packets in order to disrupt or manipulate the DetNet path/resource allocation.
An attacker can maliciously inject control packets in order to disrupt or manipulate the DetNet path/resource allocation.
A passive eavesdropper can gather information about en route DetNet flows, e.g., the number of DetNet flows, their bandwidths, and their schedules. The gathered information can later be used to invoke other attacks on some or all of the flows.
An attacker can use any of the threats described in [RFC7384] to attack the synchronization protocol, thus affecting the DetNet service.
A summary of the threats that were discussed in this section is presented in Figure 1. For each threat, the table specifies the type of attackers that may invoke the attack. In the context of this summary, the distinction between internal and external attacks is under the assumption that a corresponding security mechanism is being used, and that the corresponding network equipment takes part in this mechanism.
+-----------------------------------------+----+----+----+----+
| Attack | Attacker Type |
| +---------+---------+
| |Internal |External |
| |MITM|Inj.|MITM|Inj.|
+-----------------------------------------+----+----+----+----+
|Delay attack | + | | + | |
+-----------------------------------------+----+----+----+----+
|DetNet Flow Modification or Spoofing | + | + | | |
+-----------------------------------------+----+----+----+----+
|Inter-segment Attack | + | + | | |
+-----------------------------------------+----+----+----+----+
|Replication: Increased Attack Surface | + | + | + | + |
+-----------------------------------------+----+----+----+----+
|Replication-related Header Manipulation | + | | | |
+-----------------------------------------+----+----+----+----+
|Path Manipulation | + | + | | |
+-----------------------------------------+----+----+----+----+
|Path Choice: Increased Attack Surface | + | + | + | + |
+-----------------------------------------+----+----+----+----+
|Control or Signaling Packet Modification | + | | | |
+-----------------------------------------+----+----+----+----+
|Control or Signaling Packet Injection | | + | | |
+-----------------------------------------+----+----+----+----+
|Reconnaissance | + | | + | |
+-----------------------------------------+----+----+----+----+
|Attacks on Time Sync Mechanisms | + | + | + | + |
+-----------------------------------------+----+----+----+----+
Figure 1: Threat Analysis Summary
This section collects the various statements in the currently existing DetNet Working Group drafts. For each draft, the section name and number of the quoted section is shown. The text shown here is the work of the original draft authors, quoted verbatim from the drafts. The intention is to explicitly quote all relevant text, not to summarize it.
One key to building robust real-time systems is to reduce the infinite variety of possible failures to a number that can be analyzed with reasonable confidence. DetNet aids in the process by providing filters and policers to detect DetNet packets received on the wrong interface, or at the wrong time, or in too great a volume, and to then take actions such as discarding the offending packet, shutting down the offending DetNet flow, or shutting down the offending interface.
It is also essential that filters and service remarking be employed at the network edge to prevent non-DetNet packets from being mistaken for DetNet packets, and thus impinging on the resources allocated to DetNet packets.
There exist techniques, at present and/or in various stages of standardization, that can perform these fault mitigation tasks that deliver a high probability that misbehaving systems will have zero impact on well-behaved DetNet flows, except of course, for the receiving interface(s) immediately downstream of the misbehaving device. Examples of such techniques include traffic policing functions (e.g. [RFC2475]) and separating flows into per-flow rate- limited queues.
Security in the context of Deterministic Networking has an added dimension; the time of delivery of a packet can be just as important as the contents of the packet, itself. A man-in-the-middle attack, for example, can impose, and then systematically adjust, additional delays into a link, and thus disrupt or subvert a real-time application without having to crack any encryption methods employed. See [RFC7384] for an exploration of this issue in a related context.
Furthermore, in a control system where millions of dollars of equipment, or even human lives, can be lost if the DetNet QoS is not delivered, one must consider not only simple equipment failures, where the box or wire instantly becomes perfectly silent, but bizarre errors such as can be caused by software failures. Because there is essential no limit to the kinds of failures that can occur, protecting against realistic equipment failures is indistinguishable, in most cases, from protecting against malicious behavior, whether accidental or intentional.
Security must cover:
This document does not add any new security considerations beyond what the referenced technologies already have.
Security in the context of Deterministic Networking has an added dimension; the time of delivery of a packet can be just as important as the contents of the packet, itself. A man-in-the-middle attack, for example, can impose, and then systematically adjust, additional delays into a link, and thus disrupt or subvert a real-time application without having to crack any encryption methods employed. See [RFC7384] for an exploration of this issue in a related context.
Typical control networks today rely on complete physical isolation to prevent rogue access to network resources. DetNet enables the virtualization of those networks over a converged IT/OT infrastructure. Doing so, DetNet introduces an additional risk that flows interact and interfere with one another as they share physical resources such as Ethernet trunks and radio spectrum. The requirement is that there is no possible data leak from and into a deterministic flow, and in a more general fashion there is no possible influence whatsoever from the outside on a deterministic flow. The expectation is that physical resources are effectively associated with a given flow at a given point of time. In that model, Time Sharing of physical resources becomes transparent to the individual flows which have no clue whether the resources are used by other flows at other times.
Security must cover:
Grid monitoring and control devices are already targets for cyber attacks, and legacy telecommunications protocols have many intrinsic network-related vulnerabilities. For example, DNP3, Modbus, PROFIBUS/PROFINET, and other protocols are designed around a common paradigm of request and respond. Each protocol is designed for a master device such as an HMI (Human Machine Interface) system to send commands to subordinate slave devices to retrieve data (reading inputs) or control (writing to outputs). Because many of these protocols lack authentication, encryption, or other basic security measures, they are prone to network-based attacks, allowing a malicious actor or attacker to utilize the request-and-respond system as a mechanism for command-and-control like functionality. Specific security concerns common to most industrial control, including utility telecommunication protocols include the following:
Although advanced telecommunications networks can assist in transforming the energy industry by playing a critical role in maintaining high levels of reliability, performance, and manageability, they also introduce the need for an integrated security infrastructure. Many of the technologies being deployed to support smart grid projects such as smart meters and sensors can increase the vulnerability of the grid to attack. Top security concerns for utilities migrating to an intelligent smart grid telecommunications platform center on the following trends:
This development of a diverse set of networks to support the integration of microgrids, open-access energy competition, and the use of network-controlled devices is driving the need for a converged security infrastructure for all participants in the smart grid, including utilities, energy service providers, large commercial and industrial, as well as residential customers. Securing the assets of electric power delivery systems (from the control center to the substation, to the feeders and down to customer meters) requires an end-to-end security infrastructure that protects the myriad of telecommunications assets used to operate, monitor, and control power flow and measurement.
"Cyber security" refers to all the security issues in automation and telecommunications that affect any functions related to the operation of the electric power systems. Specifically, it involves the concepts of:
When designing and deploying new smart grid devices and telecommunications systems, it is imperative to understand the various impacts of these new components under a variety of attack situations on the power grid. Consequences of a cyber attack on the grid telecommunications network can be catastrophic. This is why security for smart grid is not just an ad hoc feature or product, it's a complete framework integrating both physical and Cyber security requirements and covering the entire smart grid networks from generation to distribution. Security has therefore become one of the main foundations of the utility telecom network architecture and must be considered at every layer with a defense-in-depth approach. Migrating to IP based protocols is key to address these challenges for two reasons:
Securing OT (Operation technology) telecommunications over packet- switched IP networks follow the same principles that are foundational for securing the IT infrastructure, i.e., consideration must be given to enforcing electronic access control for both person-to-machine and machine-to-machine communications, and providing the appropriate levels of data privacy, device and platform integrity, and threat detection and mitigation.
When BAS field networks were developed it was assumed that the field networks would always be physically isolated from external networks and therefore security was not a concern. In today's world many BASs are managed remotely and are thus connected to shared IP networks and so security is definitely a concern, yet security features are not available in the majority of BAS field network deployments .
The management network, being an IP-based network, has the protocols available to enable network security, but in practice many BAS systems do not implement even the available security features such as device authentication or encryption for data in transit.
On top of the classical requirements for protection of control signaling, it must be noted that 6TiSCH networks operate on limited resources that can be depleted rapidly in a DoS attack on the system, for instance by placing a rogue device in the network, or by obtaining management control and setting up unexpected additional paths.
Establishing time-sensitive streams in the network entails reserving networking resources for long periods of time. It is important that these reservation requests be authenticated to prevent malicious reservation attempts from hostile nodes (or accidental misconfiguration). This is particularly important in the case where the reservation requests span administrative domains. Furthermore, the reservation information itself should be digitally signed to reduce the risk of a legitimate node pushing a stale or hostile configuration into another networking node.
Note: This is considered important for the security policy of the network, but does not affect the core DetNet architecture and design.
Industrial network scenarios require advanced security solutions. Many of the current industrial production networks are physically separated. Preventing critical flows from be leaked outside a domain is handled today by filtering policies that are typically enforced in firewalls.
This memo includes no requests from IANA.
The security considerations of DetNet networks are presented throughout this document.
| [ARINC664P7] | ARINC, "ARINC 664 Aircraft Data Network, Part 7, Avionics Full-Duplex Switched Ethernet Network", 2009. |
| [I-D.ietf-detnet-use-cases] | Grossman, E., Gunther, C., Thubert, P., Wetterwald, P., Raymond, J., Korhonen, J., Kaneko, Y., Das, S., Zha, Y., Varga, B., Farkas, J., Goetz, F., Schmitt, J., Vilajosana, X., Mahmoodi, T., Spirou, S. and P. Vizarreta, "Deterministic Networking Use Cases", Internet-Draft draft-ietf-detnet-use-cases-11, October 2016. |
| [IEEE1588] | IEEE, "IEEE 1588 Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems Version 2", 2008. |
| [RFC7384] | Mizrahi, T., "Security Requirements of Time Protocols in Packet Switched Networks", RFC 7384, DOI 10.17487/RFC7384, October 2014. |