## Summary

The `/metrics` Prometheus endpoint is **unauthenticated by default** and exposes sensitive multi-tenant data in production LiteLLM Proxy deployments. While an opt-in authentication mechanism exists (`require_auth_for_metrics_endpoint: true`), the insecure default leads to widespread real-world exposure.

This is a follow-up to #13644, which was auto-closed by the stale bot as `NOT_PLANNED` without any maintainer response — despite multiple users confirming the security impact.

## Vulnerability Details

**Type:** Information Disclosure / Tenant Isolation Bypass **Default behavior:** `/metrics` endpoint serves ~2MB of Prometheus metrics to any unauthenticated HTTP request **CVSS 3.1:** 7.5 (High) — `AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N`

## Data Exposed via `litellm_proxy_total_requests_metric` Labels

The Prometheus metrics include per-request labels that leak the following data for **every tenant**:

| Label | Sensitive Data | |-------|---------------| | `hashed_api_key` | SHA-256 hash of customer API keys | | `api_key_alias` | Human-readable key names (often containing company names) | | `team` | Team UUIDs | | `team_alias` | Company names and **employee email addr…