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User data contains encoded private key

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Metadata

Id: cloudformation-aws-user-data-contains-encoded-private-key

Provider: AWS

Platform: CloudFormation

Severity: High

Category: Encryption

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Description

Embedding private keys in instance user data (even if base64-encoded) exposes sensitive credentials that can be decoded and used to gain unauthorized access to instances and pivot within your environment.

For AWS::AutoScaling::LaunchConfiguration resources, Properties.UserData must not contain PEM private key material. This includes raw PEM headers like -----BEGIN RSA PRIVATE KEY or their base64-encoded equivalents. This rule flags UserData entries that contain base64 fragments indicative of an encoded PEM header (for example, fragments such as LS0tLS1CR) or the raw PEM text.

To remediate, store keys and secrets in a secure service (AWS Secrets Manager, Systems Manager Parameter Store) or provision access via EC2 key pairs, instance roles, or runtime retrieval from a secure store instead of hard-coding them into user data.

Secure configuration example (retrieve secret from Secrets Manager at runtime):

MyLaunchConfiguration:
  Type: AWS::AutoScaling::LaunchConfiguration
  Properties:
    ImageId: ami-0abcdef1234567890
    InstanceType: t3.micro
    IamInstanceProfile: !Ref MyInstanceProfile
    UserData:
      Fn::Base64: |
        #!/bin/bash
        aws secretsmanager get-secret-value --secret-id my-app-key --region us-east-1 --query SecretString --output text > /tmp/app-key.pem
        chmod 600 /tmp/app-key.pem

Compliant Code Examples

{
  "Resources":{
    "myLaunchConfig":{
      "Type":"AWS::AutoScaling::LaunchConfiguration",
      "Properties":{
        "ImageId":"ami-02354e95b39ca8dec",
        "SecurityGroups":[ { "Ref":"myEC2SecurityGroup" }, "myExistingEC2SecurityGroup" ],
        "InstanceType":"m1.large",
        "KeyName":{
          "Ref":"KeyName"
        },
        "UserData": "some-gibberish"
      }
    }
  }
}

---
Resources:
  myLaunchConfig2:
    Type: AWS::AutoScaling::LaunchConfiguration
    Properties:
      ImageId: "ami-02354e95b39ca8dec"
      SecurityGroups:
        - Ref: "myEC2SecurityGroup"
        - myExistingEC2SecurityGroup
      InstanceType: "m1.large"
      KeyName:
        Ref: "KeyName"
      UserData: "some-gibberish"

Non-Compliant Code Examples

{
  "Resources":{
    "myLaunchConfig3":{
      "Type":"AWS::AutoScaling::LaunchConfiguration",
      "Properties":{
        "ImageId":"ami-02354e95b39ca8dec",
        "SecurityGroups":[ { "Ref":"myEC2SecurityGroup" }, "myExistingEC2SecurityGroup" ],
        "InstanceType":"m1.large",
        "KeyName":{
          "Ref":"KeyName"
        },
        "UserData": "LS0tLS1CRUdJTiBSU0EgUFJJVkFURSBLRVktLS0tLQpzb21lS2V5"
      }
    }
  }
}

---
Resources:
  myLaunchConfig4:
    Type: AWS::AutoScaling::LaunchConfiguration
    Properties:
      ImageId: "ami-02354e95b39ca8dec"
      SecurityGroups:
        - Ref: "myEC2SecurityGroup"
        - myExistingEC2SecurityGroup
      InstanceType: "m1.large"
      KeyName:
        Ref: "KeyName"
      UserData: "LS0tLS1CRUdJTiBSU0EgUFJJVkFURSBLRVktLS0tLQpzb21lS2V5"

---
Resources:
  myLaunchConfig5:
    Type: AWS::AutoScaling::LaunchConfiguration
    Properties:
      ImageId: "ami-02354e95b39ca8dec"
      InstanceType: "m1.large"
      UserData: !Base64 "LS0tLS1CRUdJTiBSU0EgUFJJVkFURSBLRVktLS0tLQpzb21lS2V5"