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UNC3944 abused Azure Serial Console after compromising privileged identities: the console gave the group an out-of-band command path into selected virtual machines, where it established additional remote access. Serial Console does not bypass Azure authentication or grant access by itself; the danger is that a compromised identity with sufficient Azure permissions can reach a VM without relying on its usual RDP or SSH network path.
How UNC3944 gained access to Azure Serial Console
Mandiant has tracked UNC3944 as a financially motivated threat group since at least May 2022. In its May 16, 2023 report, Mandiant described an identity-compromise chain involving SMS phishing, SIM swapping, and help-desk social engineering. The attackers used the resulting access to reset multifactor authentication and obtain privileged credentials. Those credentials opened the Azure tenant; Serial Console was a later step, not the initial entry point.
How the Serial Console takeover worked
Microsoft’s Serial Console connects to a virtual machine’s serial port—ttyS0 on Linux or COM1 on Windows. It provides a text-based interface that operates independently of the VM’s network state. That makes it useful for troubleshooting, but it also offers an administrative route that does not depend on reaching the machine through ordinary RDP or SSH network connections.
- Select a VM: With compromised Azure privileges, the actor used the Azure control plane and portal to choose virtual machines.
- Open a command interface: Serial Console connected to the VM’s serial port. Mandiant reported that the first command it observed was
whoami. - Inspect and alter the host: The actor used PowerShell and Azure VM extensions. Mandiant also observed VMAccessAgent activity and Windows local administrator-group enumeration, including Event ID 4799.
- Add remote-management access: The attackers installed legitimate third-party remote-management tools, which could blend in with routine administration.
- Create another way back in: Mandiant documented a reverse SSH tunnel forwarding attacker traffic on port 12345 to the VM’s local RDP port 3389.
Mandiant characterized the technique this way: “This method of attack was unique in that it avoided many of the traditional detection methods employed within Azure and provided the attacker with full administrative access to the VM.” That describes the observed incident; Serial Console access alone should not be read as a universal guarantee of administrator-level access on every VM.
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What Serial Console does—and does not—bypass
Serial Console is an out-of-band path to a VM, not an authentication bypass into Azure. An attacker still needs a sufficiently privileged Azure identity and must satisfy the feature’s VM prerequisites. Once authorized, however, console access can avoid network controls and monitoring that focus only on RDP or SSH traffic. It can therefore expose a host even when its normal network route is restricted or unavailable.
The scope also matters: connecting to one VM does not automatically mean every VM or cloud service in the tenant is compromised. But Mandiant’s M-Trends 2024 reporting documents movement from Azure console access into Azure-hosted VMs, and its follow-on reporting describes UNC3944 targeting SaaS applications. Responders should therefore investigate the identity and tenant as well as the console session and individual VM.
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Permissions, prerequisites, and logging
Microsoft’s documentation, checked October 1, 2026, describes these access conditions and controls:
| Area | What Microsoft documents | Defensive significance |
|---|---|---|
| Azure authorization | Virtual Machine Contributor or higher rights on the VM; access to the boot-diagnostics storage account may also be required, depending on its configuration. | Limit role assignments and the Microsoft.SerialConsole/serialPorts/connect/action permission to identities that need console access. |
| VM prerequisites | Boot diagnostics must be enabled, and the VM must have a password-authenticated account. | Confirm that these prerequisites and their associated storage are configured and protected as intended. |
| Feature scope | Serial Console can be enabled or disabled at subscription scope, with access further constrained through VM-level RBAC. | Disable it where it is not needed and use narrow assignments where it is. |
| Transport and records | Microsoft documents TLS 1.2 transport and access logging in VM boot-diagnostics logs. Visible console output can also be captured there. | Protect diagnostic logs: console output may include secrets or personally identifiable information (PII) typed into the session. |
How to detect and investigate suspicious use
Do not treat a console connection event as proof of compromise on its own. Establish whether the access was expected, then correlate the identity, VM, timing, and activity that followed it.
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- Alert on
Microsoft.SerialConsole/serialPorts/connect/action. For unexpected connections, identify the initiating account, source IP, target VM, and time, then confirm whether the access matches an approved task. - Correlate Azure Activity Log records with the VM’s boot-diagnostics serial output, endpoint telemetry, and process-creation events. Review relevant VM extension and diagnostic records.
- Look for PowerShell execution, VM extension deployment, VMAccessAgent activity, newly installed remote-management software, and reverse-SSH processes. Investigate unexpected RDP enablement and forwarding from external port 12345 to local port 3389.
- Check for local administrator-group enumeration; Mandiant observed Windows Event ID 4799 in its case material. Treat it as a clue to correlate with other evidence, not as a standalone indicator.
- Protect and review boot-diagnostics logs, since they can record console output as well as access. Limit access to those logs and account for the possibility that they contain secrets or PII.
Containment and tenant-wide follow-up
- Contain compromised identities: Revoke or reset affected credentials, undo unauthorized MFA changes, and investigate the privileged account and its Azure role assignments.
- Remove access paths on affected VMs: Review and remove unauthorized extensions and remote-management tools; investigate and disable rogue reverse tunnels and unexpected RDP exposure.
- Rotate exposed secrets: Treat secrets entered into a console, or captured in its diagnostic output, as potentially exposed and rotate them as appropriate.
- Look beyond the first VM: Review other VMs and Azure activity for related access, extensions, and lateral movement. Examine federated identity and SaaS environments for follow-on activity, given Mandiant’s reporting on UNC3944’s broader cloud and SaaS targeting.
- Reduce recurrence risk: Restrict Serial Console permissions, disable the feature at subscription scope where it is unnecessary, and alert on unexpected connection actions.
The cited Mandiant reports do not publish an incident-specific victim count, VM count, or loss figure for this activity. The available reporting supports the attack method and observed behaviors, not a quantified estimate of its impact.
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Sources
- Mandiant, “SIM Swapping and Abuse of the Microsoft Azure Serial Console: Serial Is Part of a Well Balanced Attack,” May 16, 2023.
- Microsoft Learn, “Azure Serial Console – Virtual Machines” and “Azure Serial Console for Windows,” documentation checked October 1, 2026.
- Mandiant, M-Trends 2024 Special Report.
- Mandiant, “UNC3944 Targets SaaS Applications.”
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