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    6. Serverless function scanning
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    Serverless function scanning

    Prisma Cloud can scan serverless functions for vulnerabilities. Prisma Cloud supports AWS Lambda, Google Cloud Functions, and Azure Functions.
    Serverless computing is an execution model in which a cloud provider dynamically manages the allocation of machine resources and schedules the execution of functions provided by users. Serverless architectures delegate the operational responsibilities, along with many security concerns, to the cloud provider. This new model raises new security concerns, while some familiar old concerns still apply. In particular, your app itself is still prone to attack. The vulnerabilities in your code and associated dependencies are the footholds attackers use to compromise an app. Prisma Cloud can show you a function’s dependencies, and surface the vulnerabilities in those dependent components.

    Capabilities

    For serverless, Prisma Cloud can scan Node.js, Python, and Java packages. There is currently no support for AWS or Azure C# functions.
    Prisma Cloud scans are triggered by the following events:
    • When the settings change, including when new functions are added for scanning.
    • When you explicitly click the
      Scan
       button in the
      Monitor > Vulnerabilities > Functions
       page.
    • Periodically. By default, Prisma Cloud rescans serverless functions every 24 hours, but you can configure a custom interval in
      Manage > System > Scan
      .

    Scanning a serverless function

    Configure Prisma Cloud to periodically scan your serverless functions. Unlike image scanning, all function scanning is handled by Console.
    1. Open Console.
    2. Go to
      Defend > Vulnerabilities > Functions
      .
    3. Click
      Add serverless account
      .
    4. In the dialog, enter the following settings:
      1. In
        Provider
        , select your cloud platform.
      2. Specify a Region.
      3. Specify a function name.
        Wildcards are supported. See the table at the top of the page for the supported syntax and examples.
      4. Select or create credentials so that Prisma Cloud can access your account.
        • AWS — Specify either an IAM user credential (access key ID and secret access key) or IAM role.
        • Google — Specify a service key.
        • Azure — Specify a user access token.
      5. Specify a cap for the number of functions to scan.
        Prisma Cloud scans the X most recent functions, where X is the cap value.
      6. Click
        Add
        .
    5. Click the yellow save button.
    6. View the scan report. Go to
      Monitor > Vulnerabilities > Functions
      .

    Authenticating with AWS

    The serverless scanner is implemented as part of Console. The scanner requires the
    AWSLambdaReadOnlyAccess
     permissions policy.
    If authenticating with an IAM user, use the Security Token Service (STS) to temporarily issue security credentials to Prisma Cloud to scan your Lambda functions. AWS STS is considered a best practice per the AWS Well-Architected Framework. For more on how to use AWS STS, see here.
    When authenticating with an IAM user, Console can access and scan functions across multiple regions. The following dialog shows Console set up to scan Lambda functions using an IAM user with STS. The user credentials (access key ID and secret access key) were previously entered in the Prisma Cloud credentials store, and the role with the
    AWSLambdaReadOnlyAccess
     permissions policy was already created in AWS.
    The Prisma Cloud serverless scanner can also authenticate with AWS using an IAM role. If Console authenticates with AWS using an IAM role, it can only scan the functions in the region where the EC2 instance is deployed. The following dialog shows Console set up to scan Lambda functions using an IAM role:

    Scanning Azure Functions

    Azure Functions are architected differently than AWS Lambda and Google Cloud Functions. Azure function apps can hold multiple functions. The functions are not segregated from each other. They share the same file system. Rather than separately scanning each function in a function app, download the root directory of the function app, which contains all its functions, and scan them as a bundle.
    Prisma Cloud only scans Linux functions that use
    External package URL
     as the deployment technology. For more information, see Deployment technologies in Azure Functions.
    To do this, you must know the Region, Name (of the function), and Service Key. To get the Service Key, download and install the Azure CLI, then:
    1. Log into your account with a user that has the User Account Administrator role.
      $ az login
    2. Get the service key.
      $ az ad sp create-for-rbac --sdk-auth --name twistlock-azure-serverless-scanning --role contributor
      Sample output from the previous command:
      {
  "clientId": "f8e9de2o-45bd-af94-ae11-b9r8c5tfy3b6",
  "clientSecret": "4dfds482-6sdd-4dsb-b5ff-56123043c4dc",
  "subscriptionId": "ea19322m-z2bd-501c-dd11-234m547a944e",
  "tenantId": "c189c61a-6c27-41c3-9949-ca5c8cc4a624",
  "activeDirectoryEndpointUrl": "https://login.microsoftonline.com",
  "resourceManagerEndpointUrl": "https://management.azure.com/",
  "activeDirectoryGraphResourceId": "https://graph.windows.net/",
  "sqlManagementEndpointUrl": "https://management.core.windows.net:8443/",
  "galleryEndpointUrl": "https://gallery.azure.com/",
  "managementEndpointUrl": "https://management.core.windows.net/"
}
    3. Copy the JSON output, which is your secret key, and paste it into the
      Service Key
       field for your Azure credentials in Prisma Cloud Console.

    Scanning functions with twistcli

    You can also use the twistcli command line utility to scan your serverless functions. First download your serverless function as a ZIP file, then run:
    $ twistcli serverless scan <SERVERLESS_FUNCTION.ZIP>
    To view scan reports in Console, go to
    Monitor > Vulnerabilities > Functions > CI
     or
    Monitor > Compliance > Functions > CI
    .

    Twistcli Options

    • Required. Complete URI for Console, including the protocol and port. Only the HTTPS protocol is supported. By default, Console listens to HTTPS on port 8083, although your administrator can configure Console to listen on a different port.
    • Username to access Console. If not provided, the TWISTLOCK_USER environment variable will be used if defined, or "admin" is used as the default.
    • Password for the user specified with -u, --user. If not specified on the command-line, the TWISTLOCK_PASSWORD environment variable will be used if defined, or otherwise will prompt for the user’s password before the scan runs.
    • Interface with a specific supervisor Console to retrieve policy and publish results.
      Example: --project "Tenant Console"
    • Show all vulnerability details.
    • Path to Prisma Cloud CA certificate file. If no CA certificate is specified, the connection to Console is insecure.
    • Include javascript package dependencies.
    • Token to use for Prisma Cloud Console authentication. Tokens can be retrieved from the API endpoint api/v1/authenticate or from the
      Manage > Authenticate > User Certificates
       page in Console.
    • Path to the CloudFormation template file in JSON or YAML format. Prisma Cloud scans the function source code for AWS service APIs being used, compares the APIs being used to the function permissions, and reports when functions have permissions for APIs they don’t need.
    • Function name to be used in policy detection and Console results. When creating policy rules in Console, you can target specific rules to specific functions by function name. If this field is left unspecified, the function zip file name is used.
    • Report APIs used by the function
    • Publish the scan result to the Console. True by default.

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