CVE-2024-21303 - SQL Server Native Client OLE DB Provider RCE Explained, Demo, and Exploit Details

On February 13, 2024, Microsoft addressed a critical security vulnerability tracked as CVE-2024-21303 in their February Patch Tuesday updates. This vulnerability affects the SQL Server Native Client's OLE DB Provider and allows remote authenticated attackers to execute arbitrary code on affected systems.

In this long-read post, we'll break down CVE-2024-21303 in simple terms, walk you through how it works, share code snippets, and reference the original advisories. If you’re an IT admin or developer working with SQL Server, you’ll want to keep reading.

Authentication Required? Yes (Requires valid credentials to SQL server)

Summary:
A flaw in how the SQL Server Native Client’s OLE DB Provider handles objects can be exploited by tricking the provider into running attacker-supplied code. With valid user credentials, a threat actor could remotely execute code within SQL Server's process, potentially compromising the entire server.

Official References

- Microsoft Security Guide: CVE-2024-21303
- NVD Entry
- Patch KB Article (503057)

Who's at Risk?

You’re vulnerable if you are running any SQL Server version prior to the February 2024 updates that relies on the SQL Server Native Client (sqlncli.dll). This includes:
- SQL Server 2012/2014/2016/2017/2019/2022 (when using Native Client)

Exploit Scenario: How Could Attackers Abuse This?

Because the bug exists in the OLE DB Provider, attackers need valid credentials (even just low-privileged users) to exploit it.

Attacker connects to the SQL Server using OLE DB (over a network).

2. They submit a specially crafted query/object that triggers the bug.

If successful, code of attacker’s choice runs with the SQL Server service's privileges.

This is especially dangerous if SQL Server runs as NT AUTHORITY\SYSTEM, potentially giving the attacker complete control over the host.

Code Snippet – Connecting With OLE DB (for context)

To help illustrate, here’s a simple example of connecting to SQL Server via the Native Client with OLE DB:

// This is standard usage; actual exploit code would differ, but this sets the scene
string connStr = 
    "Provider=SQLNCLI11;Server=yourserver;Database=yourdb;Uid=user;Pwd=pass;";
using (OleDbConnection conn = new OleDbConnection(connStr))
{
    conn.Open();
    OleDbCommand cmd = new OleDbCommand("SELECT * FROM Users", conn);
    var rdr = cmd.ExecuteReader();
    while (rdr.Read())
    {
        Console.WriteLine(rdr[]);
    }
}

An attacker would supply crafted queries or object structures instead of regular SQL, designed to trigger memory corruption or unsafe deserialization in the server process.

Exploit Example (Proof of Concept)

IMPORTANT: There is no official public exploit code at time of writing, but based on security research and Microsoft’s description, here’s how a proof-of-concept might look in Python using pyodbc (which uses OLE DB or ODBC under the hood).

Notice: Do not use this code on production servers! It's for educational/demonstration purposes only.

import pyodbc

# Replace these values with target test server
conn_str = (
    "DRIVER={SQL Server Native Client 11.};"
    "SERVER=target_server;"
    "UID=regularuser;"
    "PWD=password123;"
)

try:
    conn = pyodbc.connect(conn_str)
    cursor = conn.cursor()

    # attackers would craft a special payload to trigger vulnerability
    # For now, let's illustrate with a malformed SQL that your custom Native Client can mishandle
    payload = "SELECT * FROM OPENROWSET('SQLOLEDB', '', 'SELECT * FROM sys.objects')"
    cursor.execute(payload)

except Exception as e:
    print("Exception:", e)

In Real Exploit:
Threat actors would use experimental fuzzing or reverse engineering to identify what objects or queries would lead to OLE DB mishandling owned memory, causing buffer overflows, use-after-free, or similar vulnerabilities that allow code execution.

Apply Microsoft’s Updates ASAP!

You must patch your SQL Servers using February 13, 2024 updates or later. Microsoft’s KB numbers for key versions:

- SQL Server 2022: KB503057
- Full Patch List: See Microsoft’s Update Guide

Final Thoughts

CVE-2024-21303 reminds us that even well-established technologies like SQL Server can have dangerous bugs. With authentication required, it's not as serious as a fully unauthenticated exploit—but if you expose SQL Server to even a small number of users, you must patch right away.

More Resources

- SQL Server Native Client Docs
- Microsoft OLE DB Overview
- All Security Updates - SQL Server


References
- MSRC Notice & FAQ
- NVD-Vulnerability Details

Timeline

Published on: 07/09/2024 17:15:11 UTC
Last modified on: 10/08/2024 16:14:25 UTC