Segmentation and Lateral Movement in a Hybrid Network
A healthcare provider, HealthNet, has a hybrid network with on-premises data centers and AWS cloud. The on-premises network uses a flat VLAN for all servers (500 servers) and workstations (2,000). The AWS environment uses a VPC with public and private subnets, but security groups allow all traffic between the private subnets. A recent ransomware incident started on a workstation, spread to a server, and then to AWS via a VPN connection. The incident response team found that the attackers moved laterally using SMB and RDP. HealthNet's CISO wants to implement network segmentation to prevent future lateral movement. The network team proposes using VLANs and ACLs on-premises and AWS security groups and NACLs in the cloud. The application teams are concerned about breaking existing applications that rely on broad connectivity. The compliance team requires adherence to HIPAA and PCI DSS (for payment processing). The project has a budget of $200,000 and a timeline of 6 months.
1. What are the critical network segmentation gaps that enabled the ransomware spread, and how should they be addressed?
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Critical gaps: (1) Flat on-premises network: All servers and workstations on one VLAN allowed unrestricted lateral movement via SMB and RDP. (2) Overly permissive AWS security groups: Allowing all traffic between private subnets enabled attackers to move from the compromised server to AWS resources. (3) Insufficient egress filtering: The VPN connection allowed unrestricted traffic from on-prem to AWS, facilitating the spread. Addressing them: On-premises, implement micro-segmentation using VLANs based on function (e.g., workstations, servers, database, management) and enforce ACLs between VLANs, allowing only required ports and protocols. For critical servers, consider host-based firewalls. In AWS, replace broad security group rules with least-privilege rules, use NACLs for subnet-level control, and implement a transit gateway with segmentation. Also, restrict VPN traffic to only necessary destinations. Given the budget and timeline, prioritize segmentation of the most critical assets (e.g., EHR servers, payment systems) first, then expand. Use a phased approach to avoid disruption: start with monitoring mode to map dependencies, then enforce policies in stages.
2. How would you balance security requirements with application team concerns and compliance mandates?
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Balance by: (1) Engaging application teams early: Conduct workshops to map application dependencies and identify required flows. Use tools like network flow analysis to discover actual traffic patterns, reducing guesswork. (2) Phased enforcement: Begin with a 'monitor only' phase where new ACLs and security groups log but do not block, allowing teams to identify and fix issues. Then move to enforcement in stages, starting with non-critical applications. (3) Compliance alignment: HIPAA requires protecting ePHI, and PCI DSS requires network segmentation to reduce CDE scope. Document segmentation as a compensating control and use it to simplify compliance audits. (4) Budget allocation: Allocate funds for professional services to assist with dependency mapping and for next-generation firewalls if needed. Use open-source tools for monitoring to save costs. (5) Communication: Establish a regular cadence with stakeholders, provide clear timelines, and offer a exception process for urgent needs. This approach addresses application teams' fears by minimizing disruption and provides evidence of compliance.