Performing Serverless Function Security Review

Ne Zaman Kullanılır

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

Kullanma: 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 Tespit (use AWS Lambda Extensions with security agents).

Ön Gereksinimler

• AWS CLI, Azure CLI, and gcloud CLI configured with appropriate permissions
• Erişim: 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

İş Akışı

Adım 1: Enumerate All Serverless Functions and Configurations

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

aws lambda list-functions \
  --query 'Functions[*].[FunctionName,Runtime,MemorySize,Timeout,Role,VpcConfig.VpcId,Layers[*].Arn]' \
  --output table

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

az functionapp list \
  --query "[].{Name:name, Runtime:siteConfig.linuxFxVersion, ResourceGroup:resourceGroup, HttpsOnly:httpsOnly}" \
  -o table

gcloud functions list \
  --format="table(name, runtime, status, httpsTrigger.url, serviceAccountEmail, vpcConnector)"

Adım 2: Audit Execution Role Permissions

Review IAM roles attached to functions for overly permissive policies.

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

Adım 3: Check Environment Variables for Secrets

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

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

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
done

Adım 4: Review Function Triggers and Access Controls

Şunu doğrula: function triggers have appropriate authentication and authorization.

aws lambda list-function-url-configs \
  --function-name FUNCTION_NAME \
  --query 'FunctionUrlConfigs[*].[FunctionUrl,AuthType,Cors]' --output table

for func in $(aws lambda list-functions --query 'Functions[*].FunctionName' --output text); do
  policy=$(aws lambda get-policy --function-name "$func" --query 'Policy' --output text 2>/dev/null)
  if [ -n "$policy" ]; then
    echo "$policy" | python3 -c "
import json, sys
doc = json.loads(sys.stdin.read())
for stmt in doc.get('Statement', []):
    principal = stmt.get('Principal', {})
    if principal == '*' or principal == {'AWS': '*'}:
        print(f'WARNING: $func has public invoke policy: {stmt.get(\"Sid\", \"unnamed\")}')" 2>/dev/null
  fi
done

gcloud functions list --format=json | python3 -c "
import json, sys
functions = json.load(sys.stdin)
for func in functions:
    name = func.get('name', '').split('/')[-1]
    trigger = func.get('httpsTrigger', {})
    if trigger and func.get('ingressSettings') == 'ALLOW_ALL':
        print(f'WARNING: {name} allows all ingress traffic')
"

Adım 5: Analyze Function Code for Security Vulnerabilities

Review function code for common serverless security issues.

aws lambda get-function --function-name FUNCTION_NAME \
  --query 'Code.Location' --output text | xargs curl -o function.zip
unzip function.zip -d function-code/

pip install bandit
bandit -r function-code/ -f json -o bandit-results.json

npm install -g eslint @microsoft/eslint-plugin-sdl
eslint --ext .js function-code/

grep -rn "os.system\|subprocess\|eval(\|exec(" function-code/ || echo "No obvious injection patterns"
grep -rn "pickle.loads\|yaml.load\b" function-code/ || echo "No deserialization risks"

Adım 6: Run Automated Serverless Security Scanning

Execute Checkov and Prowler for automated compliance checks on serverless resources.

checkov -d ./serverless-project/ \
  --framework serverless \
  --output json > checkov-serverless.json

prowler aws \
  --checks lambda_function_no_secrets_in_variables \
           lambda_function_url_auth_type \
           lambda_function_using_supported_runtimes \
           lambda_function_not_publicly_accessible \
  -M json-ocsf \
  -o ./prowler-lambda/

Key Concepts

Term	Definition
Execution Role	IAM role assumed by a serverless function during execution that defines what AWS/cloud resources the function can access
Event Injection	Serverless-specific attack where untrusted data in the event trigger payload is used unsafely in function logic
Function URL	Direct HTTP(S) endpoint for invoking Lambda functions without API Gateway, which may be configured without authentication
Cold Start	Initial function execution that includes container provisioning, during which security agents and extensions must initialize
Resource-Based Policy	Policy attached to the function itself that defines who can invoke it, separate from the execution role
Secrets Manager Integration	Pattern of retrieving sensitive configuration from a secrets management service rather than storing in environment variables

Tools & Systems

• AWS Lambda: Primary serverless compute platform with execution roles, layers, and resource policies
• Checkov: Static analysis tool for infrastructure-as-code with serverless-specific security policies
• Prowler: Cloud security tool with Lambda-specific checks for permissions, public access, and runtime versions
• Bandit: Python static analysis tool for Tespit etme security issues in function source code
• OWASP Serverless Top 10: Security risk framework specific to serverless architectures

Common Scenarios

Scenario: Lambda Function with Admin Role Leaking Secrets via Environment Variables

Context: A security review discovers a Lambda function with AdministratorAccess execution role and database credentials stored in plaintext environment variables visible in CloudWatch logs.

Approach:

1. Enumerate the function's execution role and discover AdministratorAccess managed policy
2. Check environment variables and Bul: DB_PASSWORD, API_KEY, and STRIPE_SECRET_KEY in plaintext
3. Review CloudWatch logs and Bul: credentials printed in debug log statements
4. Şunu oluştur: scoped IAM policy granting only the specific DynamoDB and S3 actions needed
5. Migrate secrets to AWS Secrets Manager and update function to retrieve at runtime
6. Remove debug logging that outputs sensitive data
7. Rotate all exposed credentials and enable Lambda function encryption with KMS

Pitfalls: Changing a function's execution role can break it if the new role is too restrictive. Test in a staging environment first. Environment variable changes trigger a new function version, so ensure aliases and triggers are updated. Secrets Manager calls add latency; cache secrets within the execution context to avoid per-invocation lookups.

Output Format

Serverless Function Security Review
=======================================
Account: 123456789012
Functions Reviewed: 34
Review Date: 2026-02-23

CRITICAL Bul:INGS:
[SRVL-001] Overly Permissive Execution Role
  Function: payment-processor
  Role: AdministratorAccess (full AWS access)
  Required Permissions: DynamoDB:PutItem, S3:GetObject (2 actions)
  Remediation: Create scoped policy with only required permissions

[SRVL-002] Secrets in Environment Variables
  Function: payment-processor
  Variables: DB_PASSWORD, STRIPE_SECRET_KEY, API_KEY
  Risk: Visible in console, API, and CloudWatch logs
  Remediation: Migrate to Secrets Manager, remove from env vars

SUMMARY:
  Functions with admin roles:           3 / 34
  Functions with secrets in env vars:   8 / 34
  Functions with deprecated runtimes:   5 / 34
  Functions with public access:         2 / 34
  Functions without VPC:               28 / 34
  Functions with wildcard permissions: 12 / 34

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