Sensitive properties of nested blocks are shown during a plan in v12.6

[katbyte]

This an extension of:

• Sanitize kube_admin_config in terraform plan/apply output terraform-provider-azurerm#4105
• [azurerm_kubernetes_cluster] kube_admin_config should be sanitized terraform-provider-azurerm#4107
  properties marked sensitive are not being masked.

Terraform Version

terraform: 0.12.6
azurerm: 1.32.1

Terraform Configuration Files

    ssh_key {
      key_data = var.aks_public_key_data
    }
  }

  network_profile {
    network_plugin     = var.aks_network_plugin
    network_policy     = var.aks_network_policy
    dns_service_ip     = var.aks_dnsServiceIP
    docker_bridge_cidr = var.aks_dockerBridgeCidr
    service_cidr       = var.aks_serviceCidr
  }

  service_principal {
    client_id     = data.azurerm_key_vault_secret.cluster_sp_id.value
    client_secret = data.azurerm_key_vault_secret.cluster_sp_secret.value
  }

  role_based_access_control {
    enabled = true
    azure_active_directory {
      client_app_id     = var.aks_aad_clientapp_id
      server_app_id     = var.aks_aad_serverapp_id
      server_app_secret = var.aks_aad_serverapp_secret
      tenant_id         = data.azurerm_client_config.current.tenant_id
    }
  }
}

Debug Output

Crash Output

Expected Behavior

Sensitive values should be masked masked.

Actual Behavior

On a delete with a plan when there is nested sub objects with only select properties marked as sensitive some of the values are shown in plan.

The client_key and password fields in the kube_admin_config block are shown as literal strings instead of being masked. We're running terraform version 0.12.6, and you can see the provider versions in the plan output below.

Successfully configured the backend "azurerm"! Terraform will automatically
use this backend unless the backend configuration changes.

Initializing provider plugins...
- Checking for available provider plugins...
- Downloading plugin for provider "external" (terraform-providers/external) 1.2.0...
- Downloading plugin for provider "template" (terraform-providers/template) 2.1.2...
- Downloading plugin for provider "azurerm" (terraform-providers/azurerm) 1.32.1...

The following providers do not have any version constraints in configuration,
so the latest version was installed.

To prevent automatic upgrades to new major versions that may contain breaking
changes, it is recommended to add version = "..." constraints to the
corresponding provider blocks in configuration, with the constraint strings
suggested below.

* provider.azurerm: version = "~> 1.32"
* provider.external: version = "~> 1.2"
* provider.template: version = "~> 2.1"

Terraform has been successfully initialized!

You may now begin working with Terraform. Try running "terraform plan" to see
any changes that are required for your infrastructure. All Terraform commands
should now work.

If you ever set or change modules or backend configuration for Terraform,
rerun this command to reinitialize your working directory. If you forget, other
commands will detect it and remind you to do so if necessary.
Success! The configuration is valid.

Refreshing Terraform state in-memory prior to plan...
The refreshed state will be used to calculate this plan, but will not be
persisted to local or remote state storage.

azurerm_resource_group.sandboxuks1: Refreshing state... [id=/subscriptions/<SUBSCRIPTION_ID>/resourceGroups/<RESOURCEGROUP_NAME>].
module.aks-cluster.data.azurerm_client_config.current: Refreshing state...
module.aks-cluster.data.azurerm_subscription.current: Refreshing state...
module.aks-cluster.azurerm_kubernetes_cluster.aks_with_aad_parameters[0]: Refreshing state... [id=/subscriptions/<SUBSCRIPTION_ID>/resourcegroups/<RESOURCEGROUP_NAME>/providers/Microsoft.ContainerService/managedClusters/<RESOURCEGROUP_NAME>]
module.aks-cluster.azurerm_public_ip.aks_pip: Refreshing state... [id=/subscriptions/<SUBSCRIPTION_ID>/resourceGroups/<RESOURCEGROUP_NAME>_PIP/providers/Microsoft.Network/publicIPAddresses/<RESOURCEGROUP_NAME>_PIP]
module.aks-cluster.azurerm_monitor_diagnostic_setting.aks_cluster_diagnostics[0]: Refreshing state... [id=/subscriptions/<SUBSCRIPTION_ID>/resourceGroups/<RESOURCEGROUP_NAME>/providers/Microsoft.ContainerService/managedClusters/<RESOURCEGROUP_NAME>|aks-cluster-to-eventhub]

------------------------------------------------------------------------

An execution plan has been generated and is shown below.
Resource actions are indicated with the following symbols:
-/+ destroy and then create replacement
<= read (data resources)

Terraform will perform the following actions:

# module.aks-cluster.data.external.aks_agentpool_name will be read during apply
# (config refers to values not yet known)
<= data "external" "aks_agentpool_name"  {
    + id      = (known after apply)
    + program = [
        + "bash",
        + ".terraform/modules/aks-cluster/scripts/agentpool.sh",
        ]
    + query   = {
        + "rg_name" = "MC_<RESOURCEGROUP_NAME>_<RESOURCEGROUP_NAME>_uksouth"
        }
    + result  = (known after apply)
    }

# module.aks-cluster.azurerm_kubernetes_cluster.aks_with_aad_parameters[0] must be replaced
-/+ resource "azurerm_kubernetes_cluster" "aks_with_aad_parameters" {
    - api_server_authorized_ip_ranges = [] -> null
        dns_prefix                      = "<DNS_PREFIX>"
    ~ fqdn                            = "<CLUSTER_FQDN>" -> (known after apply)
    ~ id                              = "/subscriptions/<SUBSCRIPTION_ID>/resourcegroups/<RESOURCEGROUP_NAME>/providers/Microsoft.ContainerService/managedClusters/<RESOURCEGROUP_NAME>" -> (known after apply)
    ~ kube_admin_config               = [
        - {
            - client_certificate     = "<CLIENT_CERT>"
            - client_key             = "LITERAL_CLIENT_KEY_STRING" <--this is not obscured in any way, the client key is shown as a literal string
            - cluster_ca_certificate = "<CLUSTER_CA_CERT>"
            - host                   = "<HOSTNAME>"
            - password               = "LITERAL_PASSWORD_STRING" <--this is not obscured in any way, this is the current password for the kube admin config
            - username               = "clusterAdmin_<RESOURCEGROUP_NAME>_<RESOURCEGROUP_NAME>"
            },
        ] -> (known after apply)
    ~ kube_admin_config_raw           = (sensitive value)
    ~ kube_config                     = [
        - {
            - client_certificate     = ""
            - client_key             = ""
            - cluster_ca_certificate = "<CLUSTER_CA_CERT>"
            - host                   = "<HOSTNAME>"
            - password               = ""
            - username               = "clusterUser_<RESOURCEGROUP_NAME>_<RESOURCEGROUP_NAME>"
            },
        ] -> (known after apply)
    ~ kube_config_raw                 = (sensitive value)
    ~ kubernetes_version              = "1.13.9" -> "1.13.7"
        location                        = "uksouth"
        name                            = "<RESOURCEGROUP_NAME>"
    ~ node_resource_group             = "MC_<RESOURCEGROUP_NAME>_<RESOURCEGROUP_NAME>_uksouth" -> (known after apply)
        resource_group_name             = "<RESOURCEGROUP_NAME>"
    ~ tags                            = {} -> (known after apply)

    ~ addon_profile {
        + aci_connector_linux {
            + enabled     = (known after apply)
            + subnet_name = (known after apply)
            }

        + http_application_routing {
            + enabled                            = (known after apply)
            + http_application_routing_zone_name = (known after apply)
            }

        + oms_agent {
            + enabled                    = (known after apply)
            + log_analytics_workspace_id = (known after apply)
            }
        }

    ~ agent_pool_profile {
        - availability_zones  = [] -> null
            count               = 2
        + dns_prefix          = (known after apply)
        - enable_auto_scaling = false -> null
        ~ fqdn                = "<AGENTPOOL_PROFILE_FQDN>" -> (known after apply)
        - max_count           = 0 -> null
            max_pods            = 80
        - min_count           = 0 -> null
            name                = "agentpool"
        - node_taints         = [] -> null
            os_disk_size_gb     = 64
            os_type             = "Linux"
            type                = "AvailabilitySet"
            vm_size             = "Standard_DS4_v2"
            vnet_subnet_id      = "/subscriptions/<SUBSCRIPTION_ID>/resourceGroups/<RESOURCEGROUP_NAME>/providers/Microsoft.Network/virtualNetworks/<VNET_NAME>/subnets/<SUBNET_NAME>"
        }

        linux_profile {
            admin_username = "<ADMIN_USERNAME>"

            ssh_key {
                key_data = "<SSH_KEY>"
            }
        }

    ~ network_profile {
            dns_service_ip     = "10.254.0.10"
            docker_bridge_cidr = "172.17.0.1/16"
            load_balancer_sku  = "basic"
            network_plugin     = "azure"
        ~ network_policy     = "calico" -> "azure" # forces replacement
        + pod_cidr           = (known after apply)
            service_cidr       = "10.254.0.0/20"
        }

        role_based_access_control {
            enabled = true

            azure_active_directory {
                client_app_id     = "<AAD_CLIENT_ID>"
                server_app_id     = "<AAD_SERVER_ID>"
                server_app_secret = (sensitive value)
                tenant_id         = "*******"
            }
        }

    - service_principal {
        - client_id = "<SP_CLIENT_ID>" -> null
        }
    + service_principal {
        + client_id     = "<SP_CLIENT_ID>"
        + client_secret = (sensitive value)
        }
    }

# module.aks-cluster.azurerm_monitor_diagnostic_setting.aks_nsg_diagnostics[0] must be replaced
-/+ resource "azurerm_monitor_diagnostic_setting" "aks_nsg_diagnostics" {
        eventhub_authorization_rule_id = "/subscriptions/<SUBSCRIPTION_ID>/resourceGroups/<RESOURCEGROUP_ID>/providers/Microsoft.EventHub/namespaces/<NS_NAME>/AuthorizationRules/RootManageSharedAccessKey"
        eventhub_name                  = "aks-nsg-diagnostics"
    ~ id                             = "/subscriptions/<SUBSCRIPTION_ID>/resourceGroups/<RESOURCEGROUP_ID>/providers/Microsoft.Network/networkSecurityGroups/<AGENTPOOL_NAME>" -> (known after apply)
        name                           = "aks-nsg-to-eventhub"
    ~ target_resource_id             = "/subscriptions/<SUBSCRIPTION_ID>/resourceGroups/<RESOURCEGROUP_ID>/providers/Microsoft.Network/networkSecurityGroups/<AGENTPOOL_NAME>" -> (known after apply) # forces replacement

    - log {
        - category = "NetworkSecurityGroupEvent" -> null
        - enabled  = true -> null

        - retention_policy {
            - days    = 0 -> null
            - enabled = true -> null
            }
        }
    + log {
        + category = "NetworkSecurityGroupEvent"
        + enabled  = true

        + retention_policy {
            + enabled = true
            }
        }
    - log {
        - category = "NetworkSecurityGroupRuleCounter" -> null
        - enabled  = true -> null

        - retention_policy {
            - days    = 0 -> null
            - enabled = true -> null
            }
        }
    + log {
        + category = "NetworkSecurityGroupRuleCounter"
        + enabled  = true

        + retention_policy {
            + enabled = true
            }
        }
    }

Plan: 2 to add, 0 to change, 2 to destroy.

------------------------------------------------------------------------

This plan was saved to: terraform.tfplan

To perform exactly these actions, run the following command to apply:
    terraform apply "terraform.tfplan"`

Steps to Reproduce

Additional Context

References

[rahmanyusmadi]

0.12.9 has this problem too.

[apparentlymart]

I've transferred this to the plugin SDK repository because it appears to be caused by how the SDK is presenting this schema to Terraform Core.

Because this schema is marked as Computed: true, the SDK is presenting it to Terraform Core as an attribute with a list-of-objects type rather than as a block. "Sensitive" is an attribute-level idea, but it only applies to whole attributes and cannot apply to sub-paths within an attribute.

---

Within the provider protocol's schema model as currently defined, the best behavior we could support here is for the SDK to recursively check inside any schema.Schema it plans to represent to Terraform Core as an attribute to see if any of the nested schemas are marked as Sensitive. If any are marked, the SDK must then mark that entire attribute (the whole list of objects) as Sensitive.

I believe that currently the nested Sensitive flag is being discarded altogether (because the type system doesn't have a way to say "object type where nested attribute foo is sensitive") and so Terraform Core is getting no signal from the SDK that this attribute ought to be treated as sensitive.

---

Alternatively, the SDK could elect to present this construct to Terraform Core as being a block. Using a block to represent something that is fully computed has some implications around how the SDK must represent unknown values (it must be a known list of known objects with unknown values inside) but I assume the SDK must already be handling those edges in order to support Optional+Computed blocks that don't appear in the configuration at all, so 🤞 it would "just work" with the existing shims.

If we take that second path, I think we should check whether it causes any of the "but we are tolerating it because the provider is using the legacy SDK"-class warnings in TF_LOG=trace. Introducing more of those will create additional blockers for moving away from the legacy SDK model, which may be the right tradeoff to make in order to fix this issue promptly but I would still like to account for that potential technical debt so we can be aware of it moving into future work.

[katbyte]

Thanks for looking into this @apparentlymart,

I personally don't think marking the entire block as sensitive is a great UX from the users POV and would put my weight behind the 2nd option.

[alastairtree]

This issue is affecting us deploying app_serivce onto azure because the site_credential.password property is displayed in plain text into terraform plans.

This issue is causing us to leak app service deployment credentials into our deployment logs (we use Octopus Deploy) which are not considered safe storage for secrets by our infosec team. I know Octopus Deploy had to publish a CVE when they had similar bug last year.

This is an important security issue, please fix ASAP.

[paultyng]

As mentioned above, this is ultimately a limitation of Terraform core's data model. Only certain types of data actually track a Sensitive flag even though all "Attributes" in the SDK can have a Sensitive flag set. There is upstream work going on in Terraform core on sensitive values that needs to complete before we can address this in the provider SDK.

The core data model has two fundamental concepts: blocks and attributes. Blocks can hold blocks and other attributes. Attributes are typed. The type of an attribute though can be an "object" or "map" that has additional nested keys. Only attributes track this sensitive flag, blocks and fields on objects do not. The SDK's legacy model does not surface this nuance, nor does it make it easy for the developer to influence the translation to core's model directly. So even though you can set Sensitive in the SDK, the SDK doesn't always have a place to put that value (at least yet, until upstream adds additional handling for it).

All that being said, Sensitive has not historically been transitive, so use of a password downstream in a another resource for instance, would still be exposed in a plan. There is no way as Terraform works today to ensure full protection of Sensitive values, and as such you should take care to protect your logs as well as your state and plan files.