Executive Summary

CVE-2026-26190 is a critical security vulnerability in Milvus, an open-source vector database. The issue arises because Milvus exposes TCP port 9091 by default without proper authentication controls. Specifically, the /expr debug endpoint uses a weak and predictable default authentication token derived from the etcd.rootPath setting, allowing attackers to execute arbitrary internal expressions. Additionally, the full REST API is accessible on the metrics/management port without any authentication, enabling unauthenticated access to all business operations such as data manipulation and credential management.

This vulnerability allows attackers to bypass authentication, execute arbitrary code, access sensitive information, manipulate data, manage user credentials, and potentially cause denial of service or remote code execution.

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Impact Analysis

This vulnerability can have severe impacts including:

• Remote unauthenticated attackers can exfiltrate sensitive secrets and credentials such as MinIO secret keys and user credential hashes.
• Attackers can manipulate all data and collections, including creating, listing, deleting collections, inserting and querying data.
• User accounts can be managed or escalated by attackers, including creating, deleting, and modifying user credentials and passwords.
• Denial of service can be caused by shutting down the proxy service or corrupting metadata.
• Attackers can write arbitrary files on the server filesystem, potentially leading to remote code execution.

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Compliance Impact

I don't know

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Detection Guidance

[{'type': 'paragraph', 'content': 'This vulnerability can be detected by checking if the Milvus server is exposing TCP port 9091 without proper authentication. Specifically, you can test access to the /expr debug endpoint and the full REST API (/api/v1/*) on port 9091 to see if they allow unauthenticated access.'}, {'type': 'list_item', 'content': 'Use network scanning tools like nmap to check if port 9091 is open on your Milvus instances.'}, {'type': 'list_item', 'content': 'Attempt to access the /expr endpoint with a default or predictable authentication token (derived from etcd.rootPath, default "by-dev") to verify if arbitrary expression evaluation is possible.'}, {'type': 'list_item', 'content': 'Send HTTP requests to the /api/v1/* endpoints on port 9091 to check if REST API operations can be performed without authentication.'}, {'type': 'list_item', 'content': 'Example command to scan port 9091: nmap -p 9091 <target-ip>'}, {'type': 'list_item', 'content': 'Example curl command to test /expr endpoint: curl "http://<target-ip>:9091/expr?auth=by-dev&expr=1+%2B+1"'}, {'type': 'list_item', 'content': 'Example curl command to test unauthenticated REST API access: curl "http://<target-ip>:9091/api/v1/collections"'}] [4]

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Mitigation Strategies

[{'type': 'paragraph', 'content': 'Immediate mitigation steps include restricting access to port 9091 and securing or disabling vulnerable endpoints.'}, {'type': 'list_item', 'content': 'Block external access to TCP port 9091 using firewalls or network policies to prevent unauthorized network access.'}, {'type': 'list_item', 'content': 'Avoid exposing port 9091 outside of trusted internal networks, especially in containerized or cloud environments.'}, {'type': 'list_item', 'content': 'Change the default etcd.rootPath value from "by-dev" to a strong, random string to reduce the risk of predictable authentication tokens (partial mitigation).'}, {'type': 'list_item', 'content': 'Remove or disable the /expr debug endpoint in production environments or secure it with strong, non-default authentication.'}, {'type': 'list_item', 'content': 'Do not register business API routes on the metrics port (9091); separate metrics and health endpoints from application REST APIs.'}, {'type': 'list_item', 'content': 'Enforce authentication on all API endpoints regardless of the port they are served on.'}, {'type': 'list_item', 'content': 'Upgrade Milvus to version 2.5.27 or 2.6.10 or later, where this vulnerability is fixed by adding authentication to the metrics endpoint and securing the API.'}] [1, 2, 4]

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