How can you use the OSI model to identify security risks?

Layer Identification: Understand the OSI model's seven layers to pinpoint security risks at each level. Physical Layer (Layer 1): Risks involve unauthorized access to physical infrastructure, leading to data interception. Data Link Layer (Layer 2): Risks include MAC address spoofing, compromising network access. Network Layer (Layer 3): Concerns involve IP address spoofing and DoS attacks, impacting network integrity. Transport Layer (Layer 4): Risks include session hijacking, compromising ongoing communications. Session, Presentation, and Application Layers (Layers 5-7): Risks involve vulnerabilities in protocols and applications, leading to breaches.

Physically inspect the network infrastructure for any unauthorized devices or connections. Ensure that physical security measures such as access controls and surveillance systems are in place to prevent unauthorized access to network equipment.

This layer is considered to be the lowest layer out of the lot. The physical layer is responsible for the transmission of data bits via cables (fiber optics). The risk in this layer is that if the facility is not protected then a threat actor can tamper the cable to cause disruption in the service. Chances of intercepting and eavesdropping can be performed too via techniques such as tapping into network cables. Hence it's crucial to have strong perimeter security in place with regular inspections and audit of the assets.

This layer is primarily responsible for the transmission of the data frames with higher layers of the OSI stack. The risk of spoofing the protocol and address are high here, the prominent risk are Address Resolution Protocol (ARP) spoofing, Media Access Control (MAC) Address spoofing. There are also possibility of injection attacks too like Frame injection. To mitigate these risks, the organization needs to implement MAC address filtering, ACL, Network segmentation..etc.

You could implement MAC address filtering on switches so that only authorized devices can connect to the network. Note that you would need to monitor for any activity of spoofing attempts on authorized access

Network layer is responsible for the routing packets between the source and destination successfully. The various risk present in this layer are, IP spoofing where the attacker tries to copy the IP address of a legitimate user/asset in order to evade the detection and then cause DOS (Denial of Service), MiTM (Man in the middle) type of attack. To mitigate these risks, the organization needs to implement Firewall, IDS, access control list, strong encryption methods, VPN...etc.

Configure access control lists on routers and firewalls to restrict traffic based on source and destination IP addresses. Implement VPN access control to set users on the network

This layer handles end to end communication b/w devices inside the network. The risks associated with this layer are Session hijacking which also a MiTM attack where the threat actor manipulates the session to get access to services and applications. Use of outdated version of TLS (Transport layer security) v1.0/1.1 and SSL protocol is one of most common reason for Man in the middle attack. To mitigate these risks, organization needs to implement TLS v1.2/1.3, Firewall service IDS. regularly patch known vulnerabilities associated to the protocols.

Use security protocols such as TLS/SSL to encrypt data in transit between clients and servers. Implement intrusion detection systems, e.g. CISCO NGIPS, Cortex, etc...

Utilize secure session protocols for remote access to network devices. MFA(Multi Factor Authentication) is the go to for many organizations now.

I'll make a plug for a recent SANS Institute course that I took, SEC530: Defensible Security Architecture and Engineering: Implementing Zero Trust for the Hybrid Enterprise, where there was a strong and structured focus on attacks and security concerns that can easily be associated to risks for most of the OSI layers. This course did more to fill in gaps in my cyber security foundation than any other course I've taken, but be warned, achieving the certification will take a strong commitment from most.