Introduction: Modern threats need modern visibility
Virtualisation is now the backbone of modern IT environments, powering everything from cloud computing to virtual desktop infrastructures (VDI) and multi-tenant architectures. But as organisations scale these environments, they often carry forward legacy security solutions, designed for traditional, on-premises systems.
The problem? These traditional approaches aren’t keeping up with today’s threats. Most rely on in-guest agents that operate within the virtual machine itself – the same level as the threats they aim to detect. But modern attackers know how to work around these defences. Advanced threats – including rootkits and advanced persistent threats – can bypass, disable, or deceive in-guest security agents, leaving organisations blind to malicious activity.
This visibility gap poses a serious risk. Once an attacker compromises the VM, the security controls within it can no longer be trusted. To defend against modern threats, security teams need visibility that doesn't depend on the integrity of the guest operating system and in-guest agents.
This is where Virtual Machine Introspection (VMI) comes in.
VMI represents a shift in how we approach visibility in virtualised environments. Instead of placing trust in tools inside the machine, VMI operates from the hypervisor layer to monitor and analyse VM activity from the outside. It’s a fundamentally different method of looking into virtual machines – one that’s isolated, stealthy, and far more resistant to tampering – providing security teams a powerful new way to detect threats, investigate incidents, and protect workloads across their virtual infrastructure.
What is Virtual Machine Introspection (VMI) and how does it work?
Virtual Machine Introspection (VMI) is a technique that enables the monitoring and analysis of a virtual machine’s internal state – such as memory, CPU activity, running processes, and system calls – from outside the guest operating system. This is done at the hypervisor layer, which manages all VMs running on a host.
VMI is an entirely agentless approach. Unlike traditional tools that require software to be installed and maintained inside the virtual machine, security solutions that leverage the VMI capabilities of the hypervisor operate entirely from the outside. This means they are invisible and inaccessible to attackers who have compromised the VM, making them immune to tampering or evasion.
Leveraging the hypervisor’s privileged position, a core capability of VMI is its ability to directly observe the behaviour of guest VMs. It can inspect memory regions, detect unauthorised changes to kernel modules, monitor process creation, and watch for privilege escalation attempts – all without altering the VM or depending on its internal tools.
There are two primary modes of VMI:
- Live (real-time or ‘in-vivo’) introspection: This mode continuously monitors the VM while it’s running, providing immediate visibility into suspicious activities. It’s like having a security camera that’s always on, ready to catch malicious behaviour the moment it happens.
- Periodic (snapshot-based) introspection: In this mode, VMI captures a snapshot of the VM’s state, at intervals or on-demand, for analysis. Think of it like a scheduled security audit that provides a deep forensic look into what’s happened in a specific point in time to detect any suspicious changes.
VMI’s outside-in approach transforms the hypervisor into a strategic observation point, offering a clearer, more trustworthy view of what’s really happening inside virtual machines, which helps security teams detect threats that in-guest tools might miss.
How organisations use VMI to strengthen security
VMI isn’t just a promising concept, it’s a practical technology already in use. By moving security monitoring outside the virtual machine, it provides distinct advantages that are especially valuable against advanced threats in virtualised environments.
Unlike traditional tools that rely on cooperation from the operating system, VMI operates with complete isolation. It cannot be disabled by in-guest malware, and it remains undetectable by attackers who have gained control of a system. This out-of-band monitoring delivers full visibility, tamper-resistance, and stealth – capabilities that traditional security approaches simply can’t offer.
This approach is also backed by independent security guidance. The U.S. National Institute of Standards and Technology (NIST), in its Security Recommendations for Server-Based Hypervisor Platforms, advises that “solutions for security monitoring and security policy enforcement of VMs should be based outside of VMs and leverage the virtual machine introspection capabilities of the hypervisor” (HY-SR-15).
Here’s how VMI can be used across key security use cases.
Threat hunting and real-time threat detection
Advanced threats don’t announce themselves. Today’s attackers are stealthy, evasive, and increasingly adept at hiding from traditional security agents. VMI changes the game by making that evasion much harder.
By observing VM behaviour in real time from outside the guest OS, VMI allows security teams to detect:
- Stealthy malware such as rootkits or advanced persistent threats that avoid conventional detection
- Suspicious system behaviours like unauthorised process creation, memory manipulation, unusual system calls, or privilege escalation
- Zero-day activity or attacks lacking known signatures, using behavioural cues instead of static rules
- Malicious activity of any kind – known or novel, sophisticated or simple – regardless of whether other visibility mechanisms are in place or not.
Because VMI isn’t running inside the VM, malware can’t see or subvert the monitoring system. This makes it possible to spot indicators of compromise early and respond faster – before an attacker gains full control or spreads laterally.
For high-risk or sensitive workloads that demand continuous protection, VMI offers a critical outside edge. Analysts can watch what’s happening as it happens – and trust that what they’re seeing reflects reality, not a manipulated version of it – giving them a fighting chance to stop attacks before damage is done.
Forensic investigations and incident response
After a security breach, response teams need reliable data to understand what happened and how to recover. But if the attacker has corrupted the guest OS and security agents, in-guest telemetry is no longer trustworthy, or even available.
That’s where VMI shines.
Because it captures system data externally, VMI ensures persistent visibility, even after compromise. And since it does not rely on the guest OS remaining intact or trustworthy, security teams can trust the integrity of collected data. This means analysts can:
- Reconstruct attacker behaviour using untouched, reliable telemetry
- Preserve tamper-proof evidence for audits, legal investigations, or post-incident reviews
- Accelerate root cause analysis and reduce the time needed to contain and remediate threats
With VMI, responders get an unfiltered, out-of-band view of what happened before, during, and after a breach.
For organisations under regulatory pressure or managing mission-critical systems, this forensic reliability is a major advantage.
VMI as a competitive advantage for cloud and infrastructure providers
In multi-tenant cloud and hosted data centre environments, VMI provides significant benefits for both providers and their customers.
For cloud and infrastructure providers, VMI enables enhanced visibility into their own virtualised infrastructure, helping protect critical systems and meet increasing security expectations from regulators and customers alike. In many countries, these providers are considered critical infrastructure and must adhere to stricter security controls. VMI offers a way to achieve this.
At the same time, providers can embed VMI into their platforms as part of a value-added security offering. This creates a competitive advantage and unlocks new revenue streams. Customers gain access to advanced threat detection, compliance-ready logs, and better forensics – without having to install or manage in-guest agents themselves.
In other words, it’s not just about hosting virtual machines anymore – it’s about offering a deeply secure environment and next-level security services to customers.
Conclusion: VMI can be a game-changer for virtualised security
As organisations increasingly rely on virtualisation to power their operations, the limitations of traditional, in-guest security become harder to ignore. Modern threats are more evasive, stealthier, and better equipped to bypass or disable legacy security solutions. To defend virtualised environments effectively, security teams need mechanisms that match the complexity and sophistication of the infrastructure they protect and the threats they defend it against.
Virtual Machine Introspection offers a compelling answer to this challenge.
By delivering agentless, hypervisor-based visibility into virtual machines, VMI enables security visibility and monitoring that is tamper-resistant, stealthy, and resilient. It gives security teams the ability to see into VMs without depending on potentially compromised operating systems or agents. From real-time threat detection and proactive threat hunting to forensic analysis and scalable cloud protection, VMI helps organisations secure their virtual infrastructure more effectively.
Now is the time to assess your current level of visibility in your virtualised environments. Are your security controls able to detect threats operating below the radar? Can you trust the data they give you after a compromise?
If the answer is uncertain, it may be time to consider how virtual machine introspection could help close the gap and harden your defences from the hypervisor up.
