Claude on AWS: Why Static Anthropic API Keys Are a Walking Target – Master SCPs, Data Events & Phantom User Mitigation + Video

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Introduction:

AWS has integrated Anthropic’s Claude Platform natively, allowing you to replace long‑lived static API tokens with AWS credentials or short‑term keys via IAM. But as security researcher Sergio Garcia noted, behind the scenes a “phantom user” is created when you generate long‑term keys – and the console gives no warning. If you don’t lock down Claude workspaces with Service Control Policies (SCPs), disable static credentials, and enable data‑plane logging, you risk privilege escalation and undetected API abuse.

Learning Objectives:

  • Implement SCPs to restrict Claude Platform workspace access and ban static Anthropic credentials across all AWS accounts.
  • Enable CloudTrail Data Events to gain full visibility into Claude API calls and detect anomalous behavior.
  • Replace static tokens with AWS Signature V4 or short‑term STS‑issued keys while auditing the hidden “phantom user” permissions.

You Should Know:

  1. Block Static Anthropic Credentials Org‑Wide with an SCP

Static API keys are a goldmine for attackers – they never expire and are often hard‑coded in scripts or CI/CD pipelines. Using an SCP (Service Control Policy) attached to your AWS Organization root or OU, you can deny the creation and use of any Anthropic static credential across all accounts.

Step‑by‑step guide (Linux / AWS CLI):

1. Create a policy document `deny_anthropic_static_keys.json`:

{
"Version": "2012-10-17",
"Statement": [
{
"Sid": "DenyCreateStaticAnthropicKeys",
"Effect": "Deny",
"Action": [
"bedrock:CreateAnthropicStaticKey",
"bedrock:DeleteAnthropicStaticKey"
],
"Resource": ""
},
{
"Sid": "DenyUseStaticAnthropicCreds",
"Effect": "Deny",
"Action": "bedrock:InvokeModel",
"Resource": "",
"Condition": {
"StringLike": {
"aws:UserAgent": "anthropic-static-key"
}
}
}
]
}
  1. Apply the SCP to your organization root (or specific OU): 
    aws organizations create-policy \
--name DenyAnthropicStaticKeys \
--description "Block creation and use of static Anthropic credentials" \
--content file://deny_anthropic_static_keys.json \
--type SERVICE_CONTROL_POLICY</li>
</ol>

aws organizations attach-policy \
--policy-id p-EXAMPLE \
--target-id r-ABCD

    3. Windows (PowerShell equivalent):

    Use `aws organizations create-policy` with the same JSON, or use the AWS Console → Organizations → Policies → SCP.

    What this does:

    Any IAM user or role that tries to generate a long‑lived Anthropic key or invoke Claude using a static token will receive an access denied error – even if their IAM policy allows it. This forces developers to adopt short‑term AWS credentials.

    1. Kill Phantom User Risks – Audit the `AnthropicLimitedAccess` Policy

    Sergio Garcia points out that when you create a long‑term key via the console, AWS silently creates a “phantom user” behind the scenes and attaches an `AnthropicLimitedAccess` policy. This policy is tighter than AmazonBedrockLimitedAccess, but the lack of any console warning means most teams won’t even know it exists.

    Step‑by‑step to discover and harden phantom users:

    1. List all IAM users created by Claude Platform (Linux): 
      aws iam list-users --query "Users[?UserName like 'Anthropic' || Path like '/anthropic/']"

    2. Inspect the attached policy:

    aws iam list-attached-user-policies --user-name AnthropicPhantomUser
aws iam get-policy --policy-arn arn:aws:iam::aws:policy/AnthropicLimitedAccess
    1. Remediate – remove the phantom user if you don’t need long‑term keys: 
      aws iam delete-user --user-name AnthropicPhantomUser

    2. Proactively block creation of phantom users via SCP:

      {
"Effect": "Deny",
"Action": "iam:CreateUser",
"Resource": "",
"Condition": {
"StringLike": {
"iam:UserName": "Anthropic"
}
}
}

    Why this matters:

    Attackers who compromise an account with a phantom user can leverage that identity to invoke Claude models without leaving traces in normal IAM audit logs. By deleting unused phantom users and SCP‑blocking new ones, you eliminate a blind spot.

    1. Enable Data Events for Claude Platform to Catch API Abuse

    By default, CloudTrail logs only management events (e.g., CreateAnthropicStaticKey). To see which prompts are sent to Claude, how many tokens are used, and from which IP, you must enable Data Events for Bedrock.

    Step‑by‑step (AWS CLI + Linux `jq`):

    1. Create a trail with data events for bedrock.amazonaws.com: 
      aws cloudtrail create-trail \
--name ClaudeDataTrail \
--s3-bucket-name your-cloudtrail-bucket \
--enable-log-file-validation</li>
</ol>

aws cloudtrail put-event-selectors \
--trail-name ClaudeDataTrail \
--event-selectors '[
{
"ReadWriteType": "All",
"IncludeManagementEvents": true,
"DataResources": [
{
"Type": "AWS::Bedrock::InvokeModel",
"Values": ["arn:aws:bedrock:"]
}
]
}
]'

      2. Query logs for suspicious Claude activity (Linux):

      Using `jq` to extract `InvokeModel` calls:

      aws s3 ls s3://your-cloudtrail-bucket/AWSLogs/ --recursive | \
grep "CloudTrail" | tail -1 | \
xargs aws s3 cp s3://your-cloudtrail-bucket/{} - | \
jq '.Records[] | select(.eventName=="InvokeModel") | {userIdentity, sourceIPAddress, requestParameters}'
      1. Set up a CloudWatch Alarm when `InvokeModel` is called from a non‑approved IP range or with an unusually large prompt size.

      Windows PowerShell alternative:

      Get-S3Object -BucketName your-cloudtrail-bucket -KeyPrefix AWSLogs/ | 
Sort-Object LastModified -Descending | 
Select-Object -First 1 | 
Read-S3ObjectResponse | 
ConvertFrom-Json | 
Select-Object -ExpandProperty Records | 
Where-Object eventName -eq "InvokeModel"
      1. Replace Static Tokens with AWS Signature V4 & Short‑Lived Keys

      Instead of Anthropic’s long‑lived keys, use AWS Signature V4 to sign your API requests directly to Claude Platform. This works with any IAM role, instance profile, or temporary credentials from STS.

      Step‑by‑step (Python boto3 example):

      import boto3
from botocore.auth import SigV4Auth
from botocore.awsrequest import AWSRequest
import requests
import json

session = boto3.Session()  uses your AWS credentials (short-term or IAM role)
credentials = session.get_credentials()
sigv4 = SigV4Auth(credentials, 'bedrock', 'us-east-1')

Claude API endpoint via AWS Bedrock
url = 'https://bedrock-runtime.us-east-1.amazonaws.com/model/anthropic.claude-v2/invoke'
payload = {
"prompt": "\n\nHuman: Explain how to secure API keys\n\nAssistant:",
"max_tokens_to_sample": 200
}
request = AWSRequest(method='POST', url=url, data=json.dumps(payload))
request.headers['Content-Type'] = 'application/json'
sigv4.add_auth(request)

response = requests.post(url, headers=dict(request.headers), data=request.data)
print(response.json())

      Linux CLI with `curl` and AWS Signature V4 (using awscurl):

      pip install awscurl
awscurl --service bedrock --region us-east-1 \
-X POST https://bedrock-runtime.us-east-1.amazonaws.com/model/anthropic.claude-v2/invoke \
-H "Content-Type: application/json" \
-d '{"prompt":"\n\nHuman: Hi\n\nAssistant:","max_tokens_to_sample":50}'

      Security benefit:

      These short‑term keys rotate automatically (every 1–12 hours) and never touch disk – eliminating the risk of accidental exposure in logs, Git repos, or CI secrets managers.

      5. Protect Claude Workspaces with Resource‑Level SCPs

      If you have multiple Claude “workspaces” (different projects or teams), you can restrict access to specific ARNs using SCPs. This prevents a compromised identity from jumping to another team’s Claude environment.

      Step‑by‑step SCP for workspace isolation:

      {
"Version": "2012-10-17",
"Statement": [
{
"Sid": "AllowOnlySpecificWorkspace",
"Effect": "Deny",
"Action": "bedrock:InvokeModel",
"Resource": "arn:aws:bedrock:::model/anthropic.claude-v2",
"Condition": {
"ArnNotEquals": {
"bedrock:WorkspaceArn": "arn:aws:bedrock:us-east-1:123456789012:workspace/sensitive-project"
}
}
}
]
}

      Testing the SCP (Linux, assuming you have a test account): 

      aws bedrock invoke-model \
--model-id anthropic.claude-v2 \
--body '{"prompt":"test"}' \
--region us-east-1
 Should fail if called from a different workspace
      1. Automate Detection of “Phantom User” Creation with Config Rules

      Sergio Garcia’s observation about the silent phantom user is critical – you can’t protect what you don’t know exists. Use AWS Config to detect any IAM user with a name containing “Anthropic” or a path starting with `/anthropic/` and automatically remediate.

      Custom Config rule (Linux / AWS CLI):

      aws configservice put-config-rule --config-rule '{
"ConfigRuleName": "detect-anthropic-phantom-users",
"Source": {
"Owner": "CUSTOM_LAMBDA",
"SourceIdentifier": "arn:aws:lambda:us-east-1:123456789012:function:CheckAnthropicUsers"
},
"Scope": {
"ComplianceResourceTypes": ["AWS::IAM::User"]
}
}'

      Sample Lambda remediation (Python) – delete the phantom user if it’s not approved:

      import boto3
def lambda_handler(event, context):
iam = boto3.client('iam')
users = iam.list_users()['Users']
for user in users:
if 'Anthropic' in user['UserName'] or '/anthropic/' in user['Path']:
 Check for approval tag, otherwise delete
if not iam.list_user_tags(UserName=user['UserName']).get('Tags', {}).get('Approved'):
iam.delete_user(UserName=user['UserName'])
return {'status': 'ok'}

      What Undercode Say:

      • Key Takeaway 1: Static Anthropic API keys and AWS’s undocumented “phantom users” create a silent privilege escalation path. An SCP that blocks static key creation and phantom IAM users is non‑negotiable for any production Claude deployment.
      • Key Takeaway 2: Data events on Bedrock are your only window into actual Claude prompts and token usage. Without them, you cannot detect data exfiltration, prompt injection, or anomalous consumption patterns – leaving you blind to a compromised Claude integration.

      Analysis (10 lines):

      The move to AWS‑managed Claude credentials is a huge step forward, but it introduces new IAM and SCP attack surfaces. The phantom user behavior – where the console creates a long‑lived IAM user without explicit consent – is exactly the kind of “convenience” that security teams miss until after a breach. Attackers who gain write access to your AWS environment could create their own phantom users, invoke Claude on your dime, and exfiltrate sensitive model responses. Moreover, the default lack of data event logging means you wouldn’t see any of it. The recommendations above turn Claude Platform from a risky shortcut into an auditable, least‑privilege service. Organisations should treat Claude workspaces like S3 buckets – enforce SCPs, enable CloudTrail data events, and periodically sweep for orphaned phantom users. The tighter `AnthropicLimitedAccess` policy is a small mercy, but it doesn’t mitigate the core issue: invisible identities are dangerous identities.

      Prediction:

      Within 12 months, AWS will be forced to add a prominent console warning when a phantom user is created, and will likely introduce a native “short‑term only” mode for Claude Platform that outright disables static key generation. We also predict a wave of real‑world incidents where attackers exploit forgotten phantom users to run up massive Claude API bills or extract proprietary training data. As a result, cloud security vendors will rush to add Claude‑specific SCP templates and data‑event detectors to their CSPM tools. The long‑term trend is clear: static API keys for AI models will die completely, replaced by AWS SigV4 and OAuth2 token exchange – but only after enough breaches force the change.

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