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Open source and information security applications go together like peanut butter and jelly.
The transparency provided by open source in infosec applications -- what they monitor and how they work -- is especially important for packet sniffer and intrusion detection systems (IDSes) that monitor network traffic. It may also help explain the long-running dominance of Snort, the champion of open source enterprise network intrusion detection since 1998.
The transparency enabled by an open source license means anyone can examine the source code to see the detection methods used by packet sniffers to monitor and filter network traffic, from the OS level up to the application layer.
One problem with open source projects is that when leadership changes -- or when ownership of a project moves from individuals to corporations -- the projects don't always continue to be fully free to use, or support for the open source version of the project may take a back seat to a commercial version.
For example, consider Snort, first released as an open source project in 1998. Creator Martin Roesch started Sourcefire in 2001 in a move to monetize the popular IDS. But, in the years running up to Cisco's 2013 purchase of Sourcefire, the concern was that the company might allow the pursuit of profit to undermine development and support of the open source project. For example, Sourcefire sold a fully featured commercial version of Snort, complete with vendor support and immediate updates, a practice that has bedeviled other open source projects, as users often find the commercial entity gives the open source project short shrift to maximize profits.
Cisco has taken a different approach to the project, however. While the networking giant incorporates Snort technology in its Next-Generation Intrusion Prevention System (IPS) and Next-Generation Firewall products, Cisco "embraces the open source model and is committed to the GPL [GNU General Public License]." Cisco releases back to the open source project any feature or fixes to Snort technology incorporated in its commercial products.
What is an IDS and why is it important?
IDSes monitor network traffic and issue alerts when potentially malicious network traffic is detected. An IDS is designed to be a packet sniffer, a system able to monitor all packets sent on the organization's network, and IDSes use a variety of techniques to identify traffic that may be part of an attack. IDSes identify suspicious network traffic using the following detection methods:
- Network traffic signatures identify malicious traffic based on the protocols used, the source of the packets, the destination of the packet or some combination of these and other factors.
- Blocked lists of known malicious IP addresses enable the IDS to detect packets with an IP address identified as a potential threat.
- Anomalous network behavior patterns, similar to signatures, use information from threat intelligence feeds or authentication systems to identify network traffic that may be part of an attack.
IDSes can be host- or network-based. In a host-based IDS, software sensors are installed on endpoint hosts in order to monitor all inbound and outbound traffic, while, in a network-based IDS, the functionality is deployed in one or more servers that have connectivity to as many of the organization's internal networks as possible.
The intrusion detection function is an important part of a defense-in-depth strategy for network security that combines active listening, strong authentication and authorization systems, perimeter defenses and integration of security systems.
Snort, long the leader among enterprise network intrusion detection and intrusion prevention tools, is well-positioned to continue its reign with continued development from the open source community and the ongoing support of its corporate parent, Cisco.
In general terms, Snort offers three fundamental functions:
- Snort can be used as a packet sniffer, like TCPdump or Wireshark, by setting the host's network interface into promiscuous mode in order to monitor all network traffic on the local network interface and then write traffic to the console.
- Snort can log packets by writing the desired network traffic to a disk file.
- Snort's most important function is to operate as a full-featured network intrusion prevention system, by applying rules to the network traffic being monitored and issuing alerts when specific types of questionable activity are detected on the network.
Unlike Snort, which is a self-contained application, Security Onion is a complete Linux distribution that packages a toolbox of open source applications -- including Snort -- that are useful for network monitoring and intrusion detection, as well as other security functions, like log management. In addition to Snort, Security Onion includes other top intrusion detection tools, like Suricata, Zeek IDS and Wazuh.
Infosec professionals can install Security Onion on a desktop to turn it into a network security monitoring workstation or install the Security Onion distribution on endpoint systems and virtual environments to turn them into security sensors for distributed network intrusion monitors.
The Wazuh project offers enterprises a security monitoring application capable of doing threat detection, integrity monitoring, incident response and compliance. While it may be seen as a newcomer, the Wazuh project was forked from the venerable OSSEC project in 2015, and it has replaced OSSEC in many cases -- for example, in the Security Onion distribution.
Running as a host-based IDS, Wazuh uses both signatures and anomaly detection to identify network intrusions, as well as software misuse. It also can be used to collect, analyze and correlate network traffic data for use in compliance management and for incident response. Wazuh can be deployed in on-premises networks, as well as in cloud or hybrid computing environments.
First released in beta in 2009, Suricata has a respectable history as a Snort alternative. The platform shares architectural similarities with Snort. For example, it relies on signatures like Snort, and in many cases, it can even use the VRT Snort rules that Snort itself uses.
Like Snort, Suricata features IDS and IPS functionality, as well as support for monitoring high volumes of network traffic, automatic protocol detection, a scripting language and support for industry standard output formats. In addition, Suricata provides an engine for enterprise network security monitoring ecosystems.
The name may be unfamiliar, but the Zeek network security monitor is another mature open source IDS. The network analysis framework formerly known as Bro was renamed Zeek in 2018 to avoid negative associations with the old name, but the project is still as influential as ever.
More than a simple IDS/IPS, Zeek is a network analysis framework. While the primary focus is on network security monitoring, Zeek also offers more general network traffic analysis functionality.
Specifically, Zeek incorporates many protocol analyzers and is capable of tracking application layer state, which makes it ideal for flagging malicious or other harmful network traffic. It also offers a scripting language to enable greater flexibility and more powerful security.