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MediumElastic detection rulesElastic

Azure VM Serial Console Connection with Unusual User and ASN

Identifies a connection to the Azure Serial Console of a virtual machine (VM) by an identity and source network combination that has not been observed recently. The Serial Console provides text-based console access…

Description

Identifies a connection to the Azure Serial Console of a virtual machine (VM) by an identity and source network combination that has not been observed recently. The Serial Console provides text-based console access to a VM through the boot diagnostics serial port, independent of the VM's network state. Because it does not traverse the VM's network interface, a Serial Console session bypasses Network Security Groups (NSGs), Just-in-Time (JIT) access policies, and other network controls. An adversary with a privileged Azure RBAC role (for example Virtual Machine Contributor) and boot diagnostics enabled on the target can use the Serial Console to obtain an interactive session as SYSTEM (Windows) or root (Linux).

Detection logic

Its licence does not clear it for publishing here

Sunturai publishes a detection's own text where the licence it arrived under has been reviewed and permits it, and Elastic License 2.0 has not. The query as its source wrote it, its canonical form and the hash that pins this revision are in the workspace record.

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Detection requirements

Platform
ContainersESXiIaaSIdentity ProviderLinuxmacOSNetwork DevicesOffice SuiteSaaSWindows

The rule states no platform. This is derived from the 2 ATT&CK techniques it maps to.

Log source category
event_index

Known benign triggers

  • System or platform administrators may legitimately use the Serial Console to troubleshoot a VM that is unreachable over the network (boot failures, misconfigured firewall/NSG, lost SSH/RDP access). The first connection per identity and source ASN will alert; baseline expected break-glass principals and their corporate/VPN networks and exclude them if verified as authorized.

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