On June 2024 Patch Tuesday, Microsoft released a critical security advisory for a new vulnerability in SQL Server Native Client, tracked as CVE-2024-38255. This remote code execution (RCE) bug can let an attacker run malicious code on a target Windows system — and it’s already raising concerns among IT pros and security researchers.

In this long-read post, we’ll take a deep look at CVE-2024-38255. We’ll explain what the vulnerability is, why it matters, how it works, and go step-by-step over a proof-of-concept exploit. At the end, we'll provide simple mitigation steps and links to official guidance.

What Is CVE-2024-38255?

CVE-2024-38255 affects the SQL Server Native Client (also known as sqlncli), which is a data access API used by many Windows applications and services to connect to Microsoft SQL databases.

What makes it serious?

A specially crafted packet or SQL query can exploit this bug and let an attacker execute arbitrary code remotely with the privileges of the SQL Service account, which is often highly privileged on enterprise networks.

Affected products: Microsoft SQL Server Native Client (2012, 2014, 2016, and maybe others)

- Severity: Critical (CVSS score 9.8/10)

How Does the Exploit Work?

The flaw lies in how SQL Server Native Client parses authentication or database connection requests. When a crafted input is sent—often as a malicious SQL statement or through a malformed data packet—it can trigger a memory corruption, buffer overflow, or pointer dereference.

This is dangerous because, with precise input, the attacker can make the program run their own code in the context of the system or service account.

Exploit Flow

1. Attacker sends a malicious connection request to an application or service that uses SQL Server Native Client.

Let’s look at a hypothetical code snippet to show how one might exploit CVE-2024-38255

*Note: This is a minimal educational example. DO NOT use this for malicious purposes.*

This PoC sends a buggy packet to a TCP port used by SQL Server (default 1433)

import socket

# Target SQL Server host and port
host = 'victim-server.local'
port = 1433

# Simulated malicious payload (may trigger the vuln)
payload = b'\x12\x01\x00\x20' + b'A' * 2048  # Overlong buffer

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect((host, port))
s.sendall(payload)
print("Payload sent, check server for impact.")
s.close()

Depending on the SQL Server version and the configuration, this could cause the service to crash (denial-of-service) or, with more advanced payloads, allow the attacker to execute code.

Real-World Impact

Imagine critical business apps like accounting, HR, or customer record systems going down or being taken over by ransomware, just because of an unpatched SQL Server Native Client installation. Since the exploit is network-accessible, attackers can spread inside a company’s network by jumping from server to server.

Microsoft has fixed CVE-2024-38255 in June 2024 updates for SQL Server Native Client.

- Microsoft Security Guide: CVE-2024-38255
- SQL Server Native Client updates

Run tools like Event Viewer (eventvwr.msc) and look for service failures or access violations.

5. Enable intrusion prevention (IDS/IPS) — many solutions may block basic exploits.

References

- Microsoft CVE-2024-38255 Security Advisory
- SQL Server Native Client Download & Updates
- Rapid7 Analysis
- NIST NVD Entry
- Twitter/X search: #CVE202438255

Final Thoughts

CVE-2024-38255 is a sobering reminder that even trusted, long-standing software components like SQL Server Native Client can have vulnerabilities with massive impact. In a world where business and critical infrastructure rely on Microsoft SQL Server, this kind of bug is a juicy target for cybercriminals.

Patch your systems immediately and review your network hardening—don’t leave your data at risk. For more technical details and updates, follow Microsoft’s MSRC blog and trusted security advisories.

Timeline

Published on: 11/12/2024 18:15:21 UTC
Last modified on: 01/01/2025 00:14:28 UTC