AWS IAM Best Practices

AWS IAM Best Practices

Review and harden IAM policies following AWS security best practices and least privilege principles.

When to Use

Use this skill when you need to review IAM policies, implement least privilege access, or harden IAM security.

Core Principles

Least Privilege

• Grant minimum permissions needed
• Use managed policies when possible
• Avoid wildcard (*) permissions
• Regular access reviews

Defense in Depth

• Enable MFA for all users
• Use IAM roles instead of access keys
• Implement service control policies (SCPs)
• Enable CloudTrail for audit

Separation of Duties

• Separate admin and user roles
• Use different roles for different environments
• Implement approval workflows
• Regular permission audits

IAM Security Checks

Find Overly Permissive Policies

# List policies with full admin access
aws iam list-policies --scope Local \
  --query 'Policies[*].[PolicyName,Arn]' --output table | \
  grep -i admin

# Find policies with wildcard actions
aws iam list-policies --scope Local --query 'Policies[*].Arn' --output text | \
while read arn; do
  version=$(aws iam get-policy --policy-arn "$arn" \
    --query 'Policy.DefaultVersionId' --output text)
  doc=$(aws iam get-policy-version --policy-arn "$arn" \
    --version-id "$version" --query 'PolicyVersion.Document')
  if echo "$doc" | grep -q '"Action": "\*"'; then
    echo "Wildcard action in: $arn"
  fi
done

# Find inline policies (should use managed policies)
aws iam list-users --query 'Users[*].UserName' --output text | \
while read user; do
  policies=$(aws iam list-user-policies --user-name "$user" \
    --query 'PolicyNames' --output text)
  if [ -n "$policies" ]; then
    echo "Inline policies on user $user: $policies"
  fi
done

MFA Enforcement

# List users without MFA
aws iam get-credential-report --output text | \
  awk -F, 'NR>1 && $4=="false" {print $1}'

# Check if MFA is required in policies
aws iam list-policies --scope Local --query 'Policies[*].Arn' --output text | \
while read arn; do
  version=$(aws iam get-policy --policy-arn "$arn" \
    --query 'Policy.DefaultVersionId' --output text)
  doc=$(aws iam get-policy-version --policy-arn "$arn" \
    --version-id "$version" --query 'PolicyVersion.Document')
  if echo "$doc" | grep -q "aws:MultiFactorAuthPresent"; then
    echo "MFA enforced in: $arn"
  fi
done

# Enable MFA for a user (returns QR code)
aws iam create-virtual-mfa-device \
  --virtual-mfa-device-name user-mfa \
  --outfile /​tmp/​qr.png \
  --bootstrap-method QRCodePNG

Access Key Management

# Find old access keys (>90 days)
aws iam list-users --query 'Users[*].UserName' --output text | \
while read user; do
  aws iam list-access-keys --user-name "$user" \
    --query 'AccessKeyMetadata[*].[AccessKeyId,CreateDate,Status]' \
    --output text | \
  while read key_id create_date status; do
    age_days=$(( ($(date +%s) - $(date -d "$create_date" +%s)) / 86400 ))
    if [ $age_days -gt 90 ]; then
      echo "$user: Key $key_id is $age_days days old"
    fi
  done
done

# Rotate access key
OLD_KEY="AKIAIOSFODNN7EXAMPLE"
USER="myuser"

# Create new key
NEW_KEY=$(aws iam create-access-key --user-name "$USER")
echo "New key created. Update applications, then run:"
echo "aws iam delete-access-key --user-name $USER --access-key-id $OLD_KEY"

# Deactivate old key (test first)
aws iam update-access-key \
  --user-name "$USER" \
  --access-key-id "$OLD_KEY" \
  --status Inactive

Role and Policy Analysis

# List unused roles (no activity in 90 days)
aws iam list-roles --query 'Roles[*].[RoleName,RoleLastUsed.LastUsedDate]' \
  --output text | \
while read role last_used; do
  if [ "$last_used" = "None" ]; then
    echo "Never used: $role"
  fi
done

# Find roles with trust relationships to external accounts
aws iam list-roles --query 'Roles[*].RoleName' --output text | \
while read role; do
  trust=$(aws iam get-role --role-name "$role" \
    --query 'Role.AssumeRolePolicyDocument')
  if echo "$trust" | grep -q '"AWS":'; then
    echo "External trust: $role"
  fi
done

# Analyze policy permissions
aws iam simulate-principal-policy \
  --policy-source-arn arn:aws:iam::123456789012:user/​myuser \
  --action-names s3:GetObject s3:PutObject \
  --resource-arns arn:aws:s3:::mybucket/​*

IAM Policy Templates

Least Privilege S3 Access

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": [
        "s3:GetObject",
        "s3:PutObject"
      ],
      "Resource": "arn:aws:s3:::my-bucket/​user-data/​${aws:username}/​*"
    },
    {
      "Effect": "Allow",
      "Action": "s3:ListBucket",
      "Resource": "arn:aws:s3:::my-bucket",
      "Condition": {
        "StringLike": {
          "s3:prefix": "user-data/​${aws:username}/​*"
        }
      }
    }
  ]
}

MFA-Required Policy

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Deny",
      "Action": "*",
      "Resource": "*",
      "Condition": {
        "BoolIfExists": {
          "aws:MultiFactorAuthPresent": "false"
        }
      }
    }
  ]
}

Time-Based Access

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": "ec2:*",
      "Resource": "*",
      "Condition": {
        "DateGreaterThan": {
          "aws:CurrentTime": "2026-01-01T00:00:00Z"
        },
        "DateLessThan": {
          "aws:CurrentTime": "2026-12-31T23:59:59Z"
        }
      }
    }
  ]
}

IP-Restricted Access

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Deny",
      "Action": "*",
      "Resource": "*",
      "Condition": {
        "NotIpAddress": {
          "aws:SourceIp": [
            "203.0.113.0/​24",
            "198.51.100.0/​24"
          ]
        }
      }
    }
  ]
}

IAM Hardening Checklist

User Management

• Enable MFA for all users
• Remove unused IAM users
• Rotate access keys every 90 days
• Use IAM roles instead of long-term credentials
• Implement password policy (length, complexity, rotation)

Policy Management

• Replace inline policies with managed policies
• Remove wildcard (*) permissions
• Implement least privilege
• Use policy conditions (MFA, IP, time)
• Regular policy reviews

Role Management

• Use roles for EC2 instances
• Implement cross-account roles properly
• Review trust relationships
• Remove unused roles
• Use session tags for fine-grained access

Monitoring

• Enable CloudTrail for IAM events
• Set up CloudWatch alarms for IAM changes
• Use AWS IAM Access Analyzer
• Regular access reviews
• Monitor for privilege escalation

Automated IAM Hardening

#!/​usr/​bin/​env python3
# iam-hardening.py

import boto3
from datetime import datetime, timedelta

iam = boto3.client('iam')

def enforce_mfa():
    """Identify users without MFA"""
    users = iam.list_users()['Users']
    no_mfa = []
    
    for user in users:
        mfa_devices = iam.list_mfa_devices(
            UserName=user['UserName']
        )['MFADevices']
        
        if not mfa_devices:
            no_mfa.append(user['UserName'])
    
    return no_mfa

def rotate_old_keys():
    """Find access keys older than 90 days"""
    users = iam.list_users()['Users']
    old_keys = []
    
    for user in users:
        keys = iam.list_access_keys(
            UserName=user['UserName']
        )['AccessKeyMetadata']
        
        for key in keys:
            age = datetime.now(key['CreateDate'].tzinfo) - key['CreateDate']
            if age.days > 90:
                old_keys.append({
                    'user': user['UserName'],
                    'key_id': key['AccessKeyId'],
                    'age_days': age.days
                })
    
    return old_keys

def find_overpermissive_policies():
    """Find policies with wildcard actions"""
    policies = iam.list_policies(Scope='Local')['Policies']
    overpermissive = []
    
    for policy in policies:
        version = iam.get_policy_version(
            PolicyArn=policy['Arn'],
            VersionId=policy['DefaultVersionId']
        )
        
        doc = version['PolicyVersion']['Document']
        for statement in doc.get('Statement', []):
            if statement.get('Action') == '*':
                overpermissive.append(policy['PolicyName'])
                break
    
    return overpermissive

if __name__ == "__main__":
    print("IAM Hardening Report")
    print("=" * 50)
    
    print("\nUsers without MFA:")
    for user in enforce_mfa():
        print(f"  - {user}")
    
    print("\nOld access keys (>90 days):")
    for key in rotate_old_keys():
        print(f"  - {key['user']}: {key['age_days']} days")
    
    print("\nOverpermissive policies:")
    for policy in find_overpermissive_policies():
        print(f"  - {policy}")

Example Prompts

• "Review my IAM policies for security issues"
• "Find users without MFA enabled"
• "Create a least privilege policy for S3 access"
• "Identify overly permissive IAM roles"
• "Generate an IAM hardening report"

Best Practices

• Use AWS managed policies when possible
• Implement policy versioning
• Test policies in non-production first
• Document policy purposes
• Regular access reviews (quarterly)
• Use IAM Access Analyzer
• Implement SCPs for organization-wide controls

Kiro CLI Integration

kiro-cli chat "Use aws-iam-best-practices to review my IAM setup"
kiro-cli chat "Create a least privilege policy with aws-iam-best-practices"

Additional Resources

• IAM Best Practices
• IAM Policy Simulator
• IAM Access Analyzer