performing-serverless-function-security-review

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# Performing Serverless Function Security Review

## When to Use

- When auditing serverless applications before production deployment
- When investigating potential data exposure through function environment variables or logs
- When assessing the blast radius of a compromised serverless function execution role
- When compliance reviews require documentation of serverless security controls
- When building secure-by-default templates for serverless deployments

**Do not use** for container or VM security assessments (use container scanning tools), for API security testing (use DAST tools on the API Gateway layer), or for real-time serverless threat detection (use AWS Lambda Extensions with security agents).

## Prerequisites

- AWS CLI, Azure CLI, and gcloud CLI configured with appropriate permissions
- Access to read function configurations, policies, and execution roles
- Prowler or Checkov for automated serverless security scanning
- SAM CLI or Serverless Framework for local function analysis
- CloudTrail, Azure Monitor, or Cloud Audit Logs enabled for function invocation monitoring

## Workflow

### Step 1: Enumerate All Serverless Functions and Configurations

List all functions across cloud providers with their runtime, memory, timeout, and network settings.

```bash
# AWS Lambda: List all functions with key security attributes
aws lambda list-functions \
  --query 'Functions[*].[FunctionName,Runtime,MemorySize,Timeout,Role,VpcConfig.VpcId,Layers[*].Arn]' \
  --output table

# Check for functions using deprecated runtimes
aws lambda list-functions \
  --query 'Functions[?Runtime==`python3.7` || Runtime==`nodejs14.x` || Runtime==`dotnetcore3.1`].[FunctionName,Runtime]' \
  --output table

# Azure Functions: List all function apps
az functionapp list \
  --query "[].{Name:name, Runtime:siteConfig.linuxFxVersion, ResourceGroup:resourceGroup, HttpsOnly:httpsOnly}" \
  -o table

# GCP Cloud Functions: List all functions
gcloud functions list \
  --format="table(name, runtime, status, httpsTrigger.url, serviceAccountEmail, vpcConnector)"
```

### Step 2: Audit Execution Role Permissions

Review IAM roles attached to functions for overly permissive policies.

```bash
# AWS: Check each Lambda function's execution role
for func in $(aws lambda list-functions --query 'Functions[*].FunctionName' --output text); do
  role_arn=$(aws lambda get-function-configuration --function-name "$func" --query 'Role' --output text)
  role_name=$(echo "$role_arn" | awk -F'/' '{print $NF}')
  echo "=== $func -> $role_name ==="

  # List attached policies
  aws iam list-attached-role-policies --role-name "$role_name" \
    --query 'AttachedPolicies[*].[PolicyName,PolicyArn]' --output table

  # Check for wildcard actions
  for policy_arn in $(aws iam list-attached-role-policies --role-name "$role_name" --query 'AttachedPolicies[*].PolicyArn' --output text); do
    version=$(aws iam get-policy --policy-arn "$policy_arn" --query 'Policy.DefaultVersionId' --output text)
    aws iam get-policy-version --policy-arn "$policy_arn" --version-id "$version" \
      --query 'PolicyVersion.Document' --output json | python3 -c "
import json, sys
doc = json.load(sys.stdin)
for stmt in doc.get('Statement', []):
    actions = stmt.get('Action', [])
    if isinstance(actions, str): actions = [actions]
    resources = stmt.get('Resource', [])
    if isinstance(resources, str): resources = [resources]
    if '*' in actions or any(a.endswith(':*') for a in actions):
        print(f'  WARNING: {stmt[\"Effect\"]} {actions} on {resources}')
" 2>/dev/null
  done
done
```

### Step 3: Check Environment Variables for Secrets

Scan function environment variables for hardcoded credentials, API keys, and database connection strings.

```bash
# AWS Lambda: Extract environment variables
for func in $(aws lambda list-functions --query 'Functions[*].FunctionName' --output text); do
  envvars=$(aws lambda get-function-configuration --function-name "$func" \
    --query 'Environment.Variables' --output json 2>/dev/null)
  if [ "$envvars" != "null" ] && [ -n "$envvars" ]; then
    echo "=== $func ==="
    echo "$envvars" | python3 -c "
import json, sys, re
vars = json.load(sys.stdin)
sensitive_patterns = [
    r'(?i)(password|secret|key|token|credential|api.?key)',
    r'(?i)(aws.?access|aws.?secret)',
    r'(?i)(database.?url|connection.?string|db.?pass)',
    r'AKIA[0-9A-Z]{16}'
]
for key, value in vars.items():
    for pattern in sensitive_patterns:
        if re.search(pattern, key) or re.search(pattern, str(value)):
            masked = value[:4] + '****' + value[-4:] if len(value) > 8 else '****'
            print(f'  SENSITIVE: {key} = {masked}')
            break
"
  fi
done

# Azure Functions: Check app settings
for app in $(az functionapp list --query "[].name" -o tsv); do
  rg=$(az functionapp show --name "$app" --query "resourceGroup" -o tsv)
  echo "=== $app ==="
  az functionapp config appsettings list \
    --name "$app" --resource-group "$rg" \
    --query "[?contains(name,'KEY') || contains(name,'SECRET') || contains(name,'PASSWORD')].{Name:name}" \
    -o table 2>/dev/null

From Njones17/AI-agent-master-cyber-skills-list, MIT.

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