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Introduction

In 2024, a serious vulnerability—CVE-2024-38109—was discovered in Microsoft Azure Health Bot, a cloud-based health conversational AI platform. This security flaw allows authenticated attackers to perform Server-Side Request Forgery (SSRF), which can be leveraged to increase their privileges within a network.

Read on for a clear explanation of the vulnerability, a look at how it works, code snippets, references, and details on how an attacker might exploit it.

What is SSRF?

Server-Side Request Forgery (SSRF) is a type of security vulnerability where an attacker tricks a server into making requests on their behalf. Attackers can exploit SSRF to interact with internal resources and services that are otherwise protected from the outside world.

Where’s the Problem?

Azure Health Bot lets users create and manage bots that interact with patients and medical data. There’s a core API endpoint that fetches data based on user input. If authentication is valid, the service retrieves information from a provided URL—sometimes without enough validation.

Key Issue:
The system fails to properly restrict or cleanse URLs submitted by authenticated users. This means an attacker logged into the Azure Health Bot platform can make the service request arbitrary URLs on its own server or network.

They submit an API request that fetches data from a user-controlled URL.

3. By submitting http://localhost/admin or internal endpoints such as http://169.254.169.254/metadata/identity/oauth2/token, the bot’s backend will fetch sensitive resources accessible only from the internal network.

Code Snippet: Proof of Concept

Suppose the vulnerable endpoint is /api/fetchResource, which takes a targetUrl parameter from POST data. Here’s a Python snippet an attacker might use:

import requests

# Replace with your own session token
headers = {
    'Authorization': 'Bearer <VALID_USER_TOKEN>',
    'Content-Type': 'application/json'
}

# SSRF payload fetching internal metadata
payload = {
    "targetUrl": "http://169.254.169.254/metadata/instance?api-version=2021-02-01";
}

resp = requests.post(
    "https://<your-healthbot-instance>.azurehealthbot.com/api/fetchResource";, 
    headers=headers, 
    json=payload
)

print(resp.text)  # May return sensitive metadata like Managed Identity tokens

Exploitation Path & Privilege Escalation

1. Collect Sensitive Data: Using SSRF, an attacker can access endpoints like Azure Metadata Service. This could yield secrets, service tokens, or internal IPs.
2. Escalate Privileges: With these tokens, the attacker may authenticate as the service itself (or other users/services in the same environment). This opens doors to further attacks, like deploying resources, dumping data, or moving laterally within the Azure network.
3. Further Moves: Depending on Azure Health Bot’s permissions, attackers might access protected databases, configurations, or even inject malicious code that runs in the context of the Health Bot.

Mitigation and Fix

Microsoft has released a fix. Vulnerable endpoints now properly validate and sanitize URLs, blocking requests to internal addresses and known metadata endpoints.

References and Further Reading

- Microsoft Security Update Guide: CVE-2024-38109
- OWASP: SSRF Explained
- Azure Health Bot Documentation

Closing Thoughts

CVE-2024-38109 is a textbook example of how overlooking SSRF in a cloud-facing API can open the door to major privilege escalation. Even endpoints accessible only to “authenticated users” must be strictly validated, especially when they handle URLs or make backend network calls.

If you run Azure Health Bot, patch your instance now and double-check any custom integrations you build. SSRF isn’t just a theoretical threat—it’s a real risk that attackers can and do use to jump barriers in the cloud.

Stay safe out there, and keep your bots locked down!

Timeline

Published on: 08/13/2024 18:15:11 UTC
Last modified on: 08/24/2024 00:06:54 UTC