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Introduction:
A newly disclosed high-severity vulnerability, CVE-2026-26117, exposes a critical flaw in the Azure Connected Machine Agent for Windows, allowing low-privileged local users to escalate to SYSTEM and subsequently hijack the machine’s cloud identity. This authentication bypass (CWE-288) transforms a managed hybrid asset into a potential beachhead for lateral movement into an organization’s Azure tenant . With a CVSS score of 7.8, this vulnerability underscores the inherent risks of hybrid management tools, where a compromise on-premises can directly translate to cloud privilege escalation .
Learning Objectives:
- Understand the technical mechanics of CVE-2026-26117 and why the Azure Arc service principal becomes a prime target.
- Learn how to enumerate Azure Arc installations and identify misconfigured service principals in a hybrid environment.
- Master the step-by-step commands and procedures to detect, mitigate, and audit against this specific escalation path.
You Should Know:
1. Understanding CVE-2026-26117: The Authentication Bypass
The vulnerability resides in how the Azure Connected Machine Agent (versions below 1.61) handles specific inter-process communication (IPC) channels on Windows hosts. An attacker with local access (or via a previously compromised low-privilege account) can exploit this flaw to bypass authentication checks for a specific named pipe or service endpoint.
Step‑by‑step guide explaining what this does and how to use it:
While a public exploit is not yet available, the theory relies on interacting with the Azure Arc agent’s local endpoints. Security researchers often probe these using tools like `AccessChk` or custom PowerShell to identify weak service permissions.
- Identify Arc Services: On a target Windows machine, list services related to Azure Arc.
Get-Service -Name Azure , himds , gc , ext
Look for services like `himds` (Hybrid Instance Metadata Service) or
GCArcService. -
Check Service Permissions: Use `sc.exe` or `AccessChk` from Sysinternals to see if low-privilege users can control the service.
accesschk64.exe -ucqv himds
If the output shows that `BUILTIN\Users` has `SERVICE_CHANGE_CONFIG` or `SERVICE_STOP` permissions, the host is misconfigured.
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Abnormal Interaction (Conceptual): An exploit would likely force the agent to re-authenticate with Azure using its managed identity, then intercept or redirect that token request to an attacker-controlled endpoint, thereby stealing the cloud identity.
2. Hunting for Azure Arc in the Environment
Before exploiting or patching, you must identify all Arc-joined machines. In a red team scenario, identifying Arc is crucial for pivoting. For blue teams, it is essential for asset inventory.
Step‑by‑step guide explaining what this does and how to use it:
A. On-Premises / Local Reconnaissance:
On a compromised host, check for the Arc agent installation folder and specific registry keys.
Check for Installation Directory Test-Path "C:\Program Files\AzureConnectedMachineAgent" Check Registry for Arc Agent Configuration Get-ItemProperty -Path "HKLM:\Software\Microsoft\AzureConnectedMachineAgent"
B. Azure Cloud Reconnaissance:
If you have read access to an Azure tenant, you can enumerate Arc resources directly.
List all Azure Arc-enabled servers in a subscription az connectedmachine list --output table Using PowerShell Get-AzConnectedMachine | Select-Object Name, Location, Status, ProvisioningState
C. Entra ID Enumeration:
Azure Arc creates service principals (managed identities) for each server. These can be identified by their Resource ID.
List all service principals and filter for Arc (HybridCompute)
az ad sp list --all --query "[?contains(appOwnerOrganizationId, 'microsoft')].{DisplayName:displayName, AppId:appId}" --output table
Look for names matching the server name or the specific Arc naming convention.
- The Service Principal Trap: Abusing the Onboarding Key
As highlighted by IBM X-Force research, the most dangerous aspect of an Arc compromise is not just local SYSTEM access, but the cloud identity . Often, the service principal used to onboard servers is over-privileged, sometimes holding the “Azure Connected Machine Resource Administrator” role.
Step‑by‑step guide explaining what this does and how to use it:
If you compromise a machine and extract the service principal credentials (often via DPAPI or from deployment scripts), you can use them to move laterally.
- Extract Credentials (Red Team): Deployment scripts often leave hardcoded secrets. Check common staging directories.
Search for common deployment script extensions containing credentials findstr /si "clientsecret" C:\Windows\Temp.ps1 C:\ProgramData.json
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Validate the Service Principal (Red Team): Once you have a Tenant ID, Client ID, and Secret, authenticate to Azure.
az login --service-principal -u <CLIENT_ID> -p <CLIENT_SECRET> --tenant <TENANT_ID> az account show
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Check Assigned Roles (Red Team): Determine the scope of the compromise.
Get the role assignments for this service principal az role assignment list --assignee <CLIENT_ID> --all --output table
If the output includes `Azure Connected Machine Resource Administrator` or
Contributor, you can run commands on all Arc-enabled servers.
4. Running Commands Across the Fleet (Lateral Movement)
With the “Azure Connected Machine Resource Administrator” role or similar, an attacker can leverage the Arc control plane to execute commands on any Arc-connected machine without ever touching the local network.
Step‑by‑step guide explaining what this does and how to use it:
1. Enumerate Arc Machines: Use the hijacked service principal to list all machines under management.
az connectedmachine list --resource-group <RG_NAME> --query "[].{Name:name}" -o tsv
- Execute a Command Remotely: Use the `connectedmachine run-command` feature to deploy malware or tools. This runs with SYSTEM privileges on the target host.
az connectedmachine run-command create ` --name "Persistence" ` --machine-name "TARGET-SERVER-01" ` --resource-group "HYBRID-RG" ` --script "powershell.exe -Command Add-LocalGroupMember -Group 'Administrators' -Member 'arc_temp_user'"
5. Mitigation: Patching and Hardening the Arc Agent
Defenders must act quickly to patch the agent and harden the associated identities.
Step‑by‑step guide explaining what this does and how to use it:
1. Verify Current Version: Check the agent version on Windows.
Get-ItemProperty "HKLM:\SOFTWARE\Microsoft\AzureConnectedMachineAgent" | Select-Object -ExpandProperty Version
If the version is below 1.61, it is vulnerable .
- Update the Agent: You can update manually or enable auto-upgrades.
Download the latest Windows agent from Microsoft Start-BitsTransfer -Source "https://aka.ms/AzureConnectedMachineAgent" -Destination "AzureConnectedMachineAgent.msi" Install silently msiexec /i AzureConnectedMachineAgent.msi /qn /norestart
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Audit Service Principal Permissions (The most critical step):
– Go to the Azure Portal -> Azure Arc -> Service Principals.
– Identify any service principal used for onboarding.
– Remove the `Azure Connected Machine Resource Administrator` role from the service principal used for onboarding if it is not strictly necessary. Replace it with the least-privilege role, `Azure Connected Machine Onboarding` .
6. Linux/Windows Command Reference for Auditing
To ensure a robust defense, use these commands to create a baseline of your hybrid environment.
Step‑by‑step guide explaining what this does and how to use it:
– Windows (PowerShell): Check for modifications to the Arc agent configuration file (a known issue in v1.61 downgrade scenarios).
Check if the agent config is read-only (which can cause disconnects) attrib "C:\ProgramData\AzureConnectedMachineAgent\Config\agentconfig.json" If it is read-only, remove the attribute attrib -r "C:\ProgramData\AzureConnectedMachineAgent\Config\agentconfig.json"
– Linux (Bash): Validate GPG signatures for Arc extensions (improved in v1.61).
sudo grep -i "signature" /var/log/azure/arc.log sudo journalctl -u himds | grep -i "extension"
– KQL Query (Azure Sentinel): Hunt for suspicious run-command usage.
AzureActivity | where OperationNameValue contains "MICROSOFT.HYBRIDCOMPUTE/MACHINES/RUNCOMMANDS/ACTION" | where TimeGenerated > ago(24h) | project Caller, Resource, OperationNameValue, _ResourceId
What Undercode Say:
- Key Takeaway 1: The management plane is the new attack surface. CVE-2026-26117 demonstrates that cloud management tools (Arc, AWS SSM, etc.) are high-value targets. Compromising the tool gives attackers a “push-button” way to compromise all connected assets.
- Key Takeaway 2: Identity is the ultimate prize. The ability to escalate from a local Windows user to a cloud service principal (managed identity) breaks the traditional perimeter. Defenders must treat the Azure Arc agent’s identity with the same sensitivity as a Domain Admin credential, applying strict RBAC controls and monitoring its activity .
This vulnerability serves as a critical reminder that hybrid security is not just about securing the endpoint or the cloud separately, but about securing the bridge between them. The assumption that a local compromise cannot affect the cloud is no longer valid. Security teams must implement just-in-time access for Arc administrators and continuously monitor for anomalous behavior from these hybrid machine identities.
Prediction:
We will see an increase in attack chains that specifically target “hybrid management agents.” As EDR solutions improve at detecting traditional malware on endpoints, adversaries will shift to using trusted management protocols (like Azure Arc’s run-command) for post-exploitation. This “living-off-the-land” approach in the cloud management landscape will become a standard TTP for ransomware groups looking to rapidly encrypt hybrid environments. Expect tooling like Cobalt Strike to integrate modules for interacting with Azure IMDS and Arc endpoints within the next 6–12 months to facilitate this kind of cloud-to-ground pivot.
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IT/Security Reporter URL:
Reported By: Ilan Kalendarov – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
