Security is hard. Network security is harder. Virtual machine (VM) security in cloud computing is harder still, because it inherits every problem from traditional hosted application security and physical network security — then layers on the additional complexities of virtual resources, software-defined networking and multi-tenant infrastructure.
The core challenge is virtual-to-resource mapping: the framework required to connect hosted software components to real underlying infrastructure. Security tools designed for physical devices were not built with virtual functions in mind, and that gap is where most cloud-VM security incidents originate.
The good news is that meaningful risk reduction is achievable through an incremental, structured approach. The four steps below address the most critical attack surfaces in cloud-virtual environments.
Step 1: Protect Hosted Elements by Segregating Them
The first and most foundational step is network isolation. Any virtual function or hosted component that does not need to be directly reachable by end users should live inside a private subnetwork with no publicly routable addresses.
Consider a simple example: three features hosted inside a virtual edge device can be deployed either directly on the service data plane (addresses visible to all network users) or inside a private subnetwork (invisible from outside). If you deploy them on the public data plane, any of those features can be probed, enumerated and attacked. Hosting and management processes also become visible and vulnerable. Isolating them behind a private subnetwork removes that exposure entirely.
This is already standard practice in container-based deployments, both on-premises and in the cloud. Application components run inside private subnetworks, and only the specific API endpoints that users are intended to reach are exposed. The same discipline must be applied to Virtual Network Functions (VNFs): expose only the user-facing interfaces, and protect everything else with non-routable, access-controlled addresses.
Practical actions
- Deploy all internal VNF components into private subnets or VPCs with no public IP assignment.
- Use security groups or firewall rules to allow inbound traffic only on explicitly required ports and from defined sources.
- Apply micro-segmentation so that compromising one hosted component does not grant lateral access to others.
Step 2: Test and Review All Components Before Deployment
External attacks get most of the attention, but an insider threat or a deliberately introduced back-door vulnerability in a hosted feature is often more dangerous. Once a compromised component is deployed into service infrastructure, it becomes a trusted insider with open pathways to other infrastructure elements.
Private subnetworks help here too. If a new component can only communicate with other components inside the same service instance, a piece of malware introduced through a back-door fault is less likely to pivot to other services or affect other tenants. The blast radius is contained.
However, containment is not a substitute for proper security testing. Operators must enforce a rigorous lifecycle management and compliance process for every hosted feature and function. This means:
- Requiring vendors and suppliers to demonstrate that all new code undergoes formal security testing before release.
- Establishing an auditable compliance workflow that operators can independently validate — not just a vendor’s self-attestation.
- Treating third-party VNF code with the same scrutiny applied to any external dependency entering a production environment.
- Performing static analysis, dynamic testing and, where possible, independent penetration testing of new virtual functions before they are admitted to the service plane.
A well-designed compliance pipeline reduces the probability of both accidental vulnerabilities and deliberately seeded back-door faults making it into production.
Step 3: Separate Management APIs from the Service Plane
Management and orchestration APIs are inherently high-value targets because they control features, functions and service behaviour at a fundamental level. Exposing infrastructure management APIs to the same network plane as service traffic — or failing to isolate them from VNF management paths — creates a direct route to catastrophic compromise.
In NFV (Network Functions Virtualization) architectures, the Virtual Network Functions Manager (VNFM) — as defined by the ETSI NFV Industry Specification Group — is a particularly critical component. The VNFM is typically supplied by the VNF vendor and requires access to both infrastructure APIs and orchestration or deployment tooling. Poor design in this component can inadvertently open a gateway between user-accessible service paths and privileged infrastructure management APIs.
Securing this layer requires the following:
- Require VNF providers to submit their VNFM architecture — particularly the connections it makes to infrastructure and deployment/management APIs — for formal review before deployment.
- Enforce the principle that no service user, VNF, or VNFM associated with one service can access the infrastructure management API of another.
- Place management and orchestration APIs on a dedicated, isolated management network that is completely unreachable from the service data plane.
- Log all access to infrastructure management and orchestration APIs. Implement alerting for any unexpected access patterns or configuration changes, and review logs regularly to detect management access leaks early.
Step 4: Keep Virtual Network Connections Secure and Tenant-Isolated
Virtual networking provides agile, software-defined connectivity that can be reconfigured rapidly as features scale or redeploy. That flexibility is also a security liability: every time a virtual network change is made, there is a risk of creating an inadvertent cross-tenant or cross-service connection.
These misconfigurations can cause three categories of harm:
- Data plane leaks — traffic from one tenant’s user network becomes visible to another.
- Control plane leaks — one tenant’s management traffic bleeds into another service’s control path.
- Influence attacks — one user gains the ability to affect the service behaviour experienced by another user.
Strict policies and change-control processes around virtual connectivity significantly reduce the probability of these errors, but they cannot eliminate it entirely. The indirect relationship between a virtual network (which connects software features) and the underlying physical network (which carries actual user traffic) makes it easy for a misconfiguration to go undetected.
A practical mitigation is to integrate a network scanner or inventory verification tool as the final step of every virtual network change procedure. The tool should:
- Enumerate all devices and virtual devices currently visible on the virtual network.
- Compare that inventory against the expected service topology.
- Fail the change and trigger an alert if any unexpected connections or devices are detected.
Automated topology validation closes the gap between the logical configuration an operator intends and the actual network state that exists.
Summary: Four Steps for Cloud VM Security
| Step | Action | Primary Risk Addressed |
|---|---|---|
| 1 | Isolate hosted elements in private subnetworks | External enumeration and direct attack |
| 2 | Certify all components before deployment | Back-door faults and insider threats |
| 3 | Separate management APIs from the service plane | Infrastructure takeover via VNFM exposure |
| 4 | Validate virtual network topology after every change | Cross-tenant data and control plane leaks |
Cloud-virtual networking is not simply traditional networking with a new label. It introduces an entirely different threat model — one that cannot be addressed by tools and practices designed for the era of purely physical network devices. Operators who treat these environments with the same security discipline they apply to physical infrastructure, while adding controls specific to the virtual layer, are best positioned to contain risk as cloud-native and NFV-based architectures continue to mature.
This article is based on a technical overview originally published by TechTarget SearchSecurity.