Guide
Unauthenticated endpoint returns user-like data
How StackSiren Deep Scan detects this issue and how to fix it. Severity typically high.
Why it matters
Unauthenticated endpoint returns user-like data is a common finding on vibe-coded and AI-built apps that ship client bundles, shared backends or platform defaults without a security pass.
StackSiren reports this from read-only checks (GET, HEAD or OPTIONS only). It does not exploit the issue.
How to fix it
Require a session or bearer token on every endpoint that returns account, profile, email or PII fields. Return 401/403 for anonymous requests and never dump whole user tables.
How StackSiren Deep Scan checks
Deep Scan runs only on hosts you have verified you own (DNS TXT or /.well-known file) and consented to test. Findings include a short evidence string; secret values are masked.
See the Acceptable Use Policy and Active scanning terms for what Deep Scan is and is not.