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THE IoT Tiny Firewalls for Tiny Things


Alan Grau, VP of IoT at Sectigo considers security integration for IoT devices


here are now billions of intelligent, connected devices showing up in almost every area imaginable, and our reliance on embedded devices is growing. The IoT encompasses the Smart Grid, networked cars, medical instruments for home and hospital use, factory control systems, and military equipment. While these devices make our lives easier and more productive, our reliance on them makes us increasingly vulnerable should these devices fail.


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As IoT devices proliferate, new vulnerabilities continue to be reported and attacks against embedded devices are on the rise. Despite this fact, almost none of these devices include a firewall to protect against Internet-based threats. Firewall technology is the foundation for network security in home and corporate networks, yet they are virtually absent in embedded systems. The number of attacks against embedded devices continues to rise. An F-Secure Report showed a 600% increase in attacks from 2018 to 2019. Reported attacks on embedded devices include:


• Attacks against web interfaces on IP cameras • Printers reprogrammed with malicious firmware that cause it to forward documents to a remote computer, or to run continuously, heating up and physically damaging the printer


• Computerised IV drips that were shut off due to a DoS attack (in a lab setting)


• Embedded devices failing from packet floods • Widespread IoT botnets, including the Mirai botnet


Filtering options


A Firewall protects an Iot device by controlling which packets pass through the firewall and are processed by the device. There are three types of filtering firewalls can provide:


• Static filtering: filter packets based only on the information in the packet. This includes filtering based on port number, protocol, IP address, etc.


• Dynamic filtering or Stateful Packet Inspection (SPI): filters packets based on the state of the connection, allowing packets to be blocked or rejected based on the connection state as well as the filtering rules


• Threshold-based filtering: keeps statistics on the number of packets received and uses threshold crossings to detect and block packet floods and DoS attacks


Depending on system requirements, an engineer may elect to use one, two or all three filtering methods.


Blocking attacks with a firewall


In a system without a firewall, a hacker may attempt to remotely access the device using default passwords, dictionary attacks, or even using stolen passwords. Such attacks are often automated, allowing a huge number of attempts to break the system’s password. An embedded firewall, configured with an IP address whitelist of trusted hosts, will block this attack. Login attempts from the hacker will be blocked by the IP address filter before a login is even attempted.


A firewall that supports complex rules allows fine grained control over the packets processed by the device for greater flexibility in the


configuration of the device. For example, the firewall for a printer could be configured with a rule that allows printer commands from any IP address. A second rule could specify that firmware upgrades are only accepted from a known list of upgrade servers. Together these rules would block malicious firmware download attacks. Embedded devices often do not have the memory, available CPU cycles or other resources found in desktop or enterprise systems. As a result, traditional firewall technology does not work well in an embedded environment. Engineers need a firewall designed specifically for smaller systems.


An embedded firewall must be small, efficient, and easily integrated with the operating system and TCP/IP stack of the embedded device.


A firewall for embedded systems An embedded firewall is designed to meet the specific requirements of embedded applications. It needs to provide static filtering, threshold-based filtering, and Stateful Packet Inspection to protect embedded devices from Internet-based threats. The firewall has a small memory footprint, low CPU processing impact and is easily integrated with any embedded IP stack.


Despite the growing risks, most embedded devices still do not include a firewall. The unique requirements of an embedded device make porting a desktop firewall impractical. A tiny embedded firewall solves this problem, providing an easy, affordable means to include a firewall in embedded devices.


Sectigo www.sectigo.com


MAY 2021 | ELECTRONICS TODAY 31


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