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Monitor OS Vulnerabilities

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Risk Level: Medium (should be achieved)
Rule ID: SecurityCenter-004

Ensure that monitoring for operating system (OS) vulnerabilities is enabled within the Microsoft Defender for Cloud security policy in order to determine if your Azure virtual machines are vulnerable to attacks. Microsoft Defender for Cloud analyzes daily the operating system of your virtual machines for configurations that could make these VMs more vulnerable to cyberattacks. Microsoft Defender for Cloud also recommends specific configuration changes that you can apply in order to address any OS vulnerability found.

This rule resolution is part of the Conformity Security & Compliance tool for Azure.

Security

When the monitoring feature is enabled, Microsoft Defender for Cloud analyzes operating system (OS) configurations on a daily basis to identify security issues that could make your organization's systems vulnerable to attacks.

Audit

To determine if the OS vulnerabilities monitoring is enabled within the Microsoft Defender for Cloud security policy, perform the following operations:

Using Azure Console

01 Sign in to the Microsoft Azure Portal.

02 Navigate to Microsoft Defender for Cloud blade at https://portal.azure.com/#blade/Microsoft_Azure_Security/SecurityMenuBlade/0.

03 In the main navigation panel, under Management, choose Environment settings.

04 Click on the name (link) of the Azure subscription that you want to examine.

05 In the navigation panel, under Policy settings, choose Security policy.

06 In the Default initiative section, click on the name of the default initiative enabled for the selected subscription (i.e. ASC Default (subscription: <subscription-id>)).

07 Choose the Parameters tab, uncheck Only show parameters that need input or review, and search for the following parameter: Vulnerabilities in security configuration on your machines should be remediated. If the Vulnerabilities in security configuration on your machines should be remediated parameter is set to Disabled, the OS vulnerabilities monitoring (based on a configured baseline) is not enabled for the selected Azure subscription.

08 Repeat steps no. 4 – 7 for each Microsoft Azure subscription created within your Azure account.

Using Azure CLI

01 Run account get-access-token command (Windows/macOS/Linux) using custom query filters to determine if the Operating System (OS) vulnerabilities monitoring is enabled within the current Azure subscription by checking the systemConfigurationsMonitoringEffect configuration parameter value: 

az account get-access-token
  --query "{subscription:subscription,accessToken:accessToken}"
  --out tsv | xargs -L1 bash -c 'curl -X GET -H "Authorization: Bearer $1" -H "Content-Type: application/json" https://management.azure.com/subscriptions/$0/providers/Microsoft.Authorization/policyAssignments/SecurityCenterBuiltIn?api-version=2018-05-01' | jq 'select(.name=="SecurityCenterBuiltIn")'|jq '.properties.parameters.systemConfigurationsMonitoringEffect.value'

02 The command output should return the requested parameter value: 

"Disabled"

If the account get-access-token command output returns "Disabled", as shown in the output example above, the OS vulnerabilities monitoring (based on a configured baseline) is not enabled within the current Azure subscription.

03 Repeat steps no. 1 and 2 for each Microsoft Azure subscription available in your Azure cloud account.

Remediation / Resolution

To enable OS vulnerabilities monitoring and recommendations for your Microsoft Azure virtual machines (VMs), perform the following operations:

Using Azure Console

01 Sign in to the Microsoft Azure Portal.

02 Navigate to Microsoft Defender for Cloud blade at https://portal.azure.com/#blade/Microsoft_Azure_Security/SecurityMenuBlade/0.

03 In the main navigation panel, under Management, choose Environment settings.

04 Click on the name (link) of the Azure subscription that you want to access.

05 In the navigation panel, under Policy settings, choose Security policy.

06 In the Default initiative section, click on the name of the default initiative enabled for the selected subscription (i.e. ASC Default (subscription: <subscription-id>)).

07 Choose the Parameters tab and uncheck the Only show parameters that need input or review checkbox to list all the initiative parameters.

08 Select AuditIfNotExists from the Vulnerabilities in security configuration on your machines should be remediated parameter dropdown list to enable the OS vulnerabilities monitoring for Azure virtual machines (VMs), in the selected Azure subscription.

09 Select Review + save to review the configuration changes, then choose Save to apply the new changes. If the operation is successful, the following confirmation message should be displayed: "Updating policy assignment succeeded".

10 Repeat steps no. 4 – 9 for each Microsoft Azure subscription available within your Azure account.

Using Azure CLI

01 Define the configuration parameters for the account get-access-token command, where the systemConfigurationsMonitoringEffect parameter is enabled to turn on the monitoring feature. Save the configuration document to a JSON file named enable-system-configurations-monitoring.json and replace the highlighted details, i.e. <azure-subscription-id> and <policy-definition-id>, with your own Azure account subscription details: 

{
  "properties":{
     "displayName":"ASC Default (subscription: <azure-subscription-id>)",
     "policyDefinitionId":"/providers/Microsoft.Authorization/policySetDefinitions/<policy-definition-id>",
     "scope":"/subscriptions/<azure-subscription-id>",
     "parameters":{
        "systemConfigurationsMonitoringEffect":{
           "value":"AuditIfNotExists"
        }
     }
  },
  "id":"/subscriptions/<azure-subscription-id>/providers/Microsoft.Authorization/policyAssignments/SecurityCenterBuiltIn",
  "type":"Microsoft.Authorization/policyAssignments",
  "name":"SecurityCenterBuiltIn",
  "location":"eastus"
}

02 Run account get-access-token command (Windows/macOS/Linux) using the configuration document defined at the previous step (i.e. enable-system-configurations-monitoring.json file), to enable the monitoring of OS vulnerabilities for Azure virtual machines (VMs), within the current Microsoft Azure subscription: 

az account get-access-token
  --query "{subscription:subscription,accessToken:accessToken}"
  --out tsv | xargs -L1 bash -c 'curl -X PUT -H "Authorization: Bearer $1" -H "Content-Type: application/json" https://management.azure.com/subscriptions/$0/providers/Microsoft.Authorization/policyAssignments/SecurityCenterBuiltIn?api-version=2018-05-01 -d@"enable-system-configurations-monitoring.json"'

03 The command output should return information about the modified configuration parameter: 

{
  "sku": {
    "name": "A0",
    "tier": "Free"
  },
  "properties": {
    "displayName": "ASC Default (subscription: abcdabcd-1234-1234-1234-abcdabcdabcd)",
    "policyDefinitionId": "/providers/Microsoft.Authorization/policySetDefinitions/1234abcd-1234-1234-1234-abcd1234abcd",
    "scope": "/subscriptions/abcdabcd-1234-1234-1234-abcdabcdabcd",
    "parameters": {
      "systemConfigurationsMonitoringEffect": {
        "value": "AuditIfNotExists"
      }
    },
    "metadata": {
      "createdBy": "abcdabcd-1234-1234-1234-abcdabcdabcd",
      "createdOn": "2019-05-17T15:38:40.3473931Z",
      "updatedBy": "1234abcd-1234-1234-1234-abcd1234abcd",
      "updatedOn": "2022-02-01T21:22:40.7422203Z"
    }
  },
  "id": "/subscriptions/abcdabcd-1234-1234-1234-abcdabcdabcd/providers/Microsoft.Authorization/policyAssignments/SecurityCenterBuiltIn",
  "type": "Microsoft.Authorization/policyAssignments",
  "name": "SecurityCenterBuiltIn",
  "location": "eastus"
}

04 Repeat steps no. 1 – 3 for each Microsoft Azure subscription available in your Azure cloud account.

References

Publication date May 21, 2019

Related SecurityCenter rules