Executive Summary

In MLflow version 3.9.0, the MLflow Assistant feature had a security flaw in its /ajax-api endpoints where it did not properly validate the origin of incoming requests.

This improper origin validation allowed a remote attacker to exploit cross-origin requests from a malicious webpage to interact with the MLflow Assistant running on a victim's local machine.

By bypassing the restriction that limited access to loopback (local) requests only, the attacker could modify the Assistant's configuration to enable full access.

With full access enabled, the attacker could execute arbitrary commands through the Claude Code sub-agent, potentially compromising the victim's system.

This vulnerability was fixed in MLflow version 3.10.0.

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Impact Analysis

This vulnerability can have severe impacts including unauthorized remote code execution on your local machine where MLflow Assistant is running.

An attacker exploiting this flaw can bypass local access restrictions and gain full control over the Assistant's configuration.

This can lead to execution of arbitrary commands, potentially resulting in data theft, system compromise, or further attacks within your environment.

Because the vulnerability allows high-level access without authentication, it poses a critical security risk.

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Detection Guidance

Detection of this vulnerability involves checking if the MLflow Assistant's /ajax-api endpoints improperly allow cross-origin requests from unauthorized origins, bypassing the loopback-only restriction.

One approach is to test CORS behavior on the /ajax-api endpoints by sending cross-origin requests from different origins and observing if the server improperly accepts them.

For example, you can use curl commands to simulate cross-origin requests with different Origin headers to see if the server responds with permissive CORS headers.

• curl -H "Origin: http://malicious.example.com" -X OPTIONS http://localhost:5000/ajax-api/some-endpoint -v
• curl -H "Origin: http://localhost" -X OPTIONS http://localhost:5000/ajax-api/some-endpoint -v

If the server responds with Access-Control-Allow-Origin headers allowing origins other than localhost or the predefined allowed origins, it indicates the vulnerability may be present.

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Mitigation Strategies

The immediate mitigation step is to upgrade MLflow to version 3.10.0 or later, where this vulnerability is resolved.

If upgrading is not immediately possible, restrict access to the MLflow Assistant service to trusted networks only, preventing untrusted web pages from reaching the /ajax-api endpoints.

Additionally, review and configure CORS settings to ensure that only trusted origins, such as localhost or explicitly allowed origins, can access the AJAX API endpoints.

Implement network-level controls such as firewall rules to block external access to the MLflow Assistant's local endpoints.

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Compliance Impact

The vulnerability in MLflow version 3.9.0 allows remote attackers to bypass origin validation and execute arbitrary commands on a victim's local machine via the MLflow Assistant's /ajax-api endpoints. This can lead to unauthorized access and control over the affected system.

Such unauthorized access and potential data manipulation or exposure could negatively impact compliance with common standards and regulations like GDPR and HIPAA, which require strict controls over data confidentiality, integrity, and system access.

By enabling attackers to execute arbitrary commands, the vulnerability increases the risk of data breaches or unauthorized data processing, which are critical concerns under these regulations.

The issue was resolved in version 3.10.0 by enhancing CORS handling to restrict allowed origins and prevent unauthorized cross-origin requests.

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