In early 2024, Microsoft revealed CVE-2024-26166, a high-severity vulnerability inside its WDAC OLE DB Provider for SQL Server. If you work with enterprise SQL deployments or Windows server security, this is a vulnerability you can’t afford to ignore. In this post, we'll explain what CVE-2024-26166 is, how it works, provide code examples, and show how attackers might exploit this bug.
What Is CVE-2024-26166?
CVE-2024-26166 is a Remote Code Execution (RCE) vulnerability affecting the Windows Data Access Components (WDAC) OLE DB Provider for SQL Server, specifically the MSOLEDBSQL driver. The bug allows an attacker to execute arbitrary code on the victim system—remotely—if they trick a user into connecting to a malicious SQL Server instance.
Severity: High (CVSS: 8.)
Impacted: All supported Windows versions running the vulnerable provider, especially in environments where users connect to untrusted SQL Server servers.
Official Microsoft Advisory:
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2024-26166
How Does the Attack Work?
When applications use OLE DB (like MSOLEDBSQL) to connect to SQL Server, a client process on the victim machine parses data sent by the server. Due to improper validation of responses, a malicious SQL Server can send specially crafted data to the client, triggering a memory corruption bug and achieving code execution on the client side.
Attack scenario:
Attacker spins up a rogue SQL Server.
2. Victim runs an app or PowerShell that tries to connect over OLE DB using a crafted connection string.
Client’s OLE DB parser is exploited, code runs with user privileges.
> This is a classic "client-side attack via malicious server"—no need for prior local access or authentication.
To show how a user might be exposed, here’s a PowerShell snippet to connect via OLE DB
$connectionString = "Provider=MSOLEDBSQL;Data Source=attacker-server;Integrated Security=SSPI;Initial Catalog=master"
$conn = New-Object System.Data.OleDb.OleDbConnection($connectionString)
$conn.Open()
If attacker-server is under an attacker’s control and is running a malicious SQL Server variant, simply opening the connection can exploit the client.
The same applies to C#, VB, or C++ software using OLE DB to access SQL.
The Exploit: What Does an Attacker Do?
An attacker needs only to lure a victim into connecting to their SQL server—maybe through a phishing email, a link in a doc, or a misconfigured connection in software.
Serve Up Exploit:
Attacker sets up a custom or patched version of SQL Server (or open-source alternative like CockroachDB) to return crafted binary data triggering the bug.
Arbitrary Code Execution:
The crafted payload abuses memory within the client’s process, loading shellcode or a reverse shell, running as the user who started the SQL connection.
Sample Pseudocode of Attack (server side)
on connect():
send malicious response in SQL protocol
# This response targets known vulnerability offsets in MSOLEDBSQL.dll
Due to the nature of the flaw, proof-of-concept (PoC) code is closely held, but patterns follow general MSOLEDBSQL protocol fuzzing and exploitation.
Example tools attackers could adapt
If You Use OLE DB for SQL Server
- Patch immediately: Apply updates from Microsoft's Patch Tuesday for March 2024.
- Block outbound connections to unknown/untrusted SQL servers.
Key References
- Microsoft Security Response Center – CVE-2024-26166
- MSOLEDBSQL documentation
- Impacket (Useful for protocol fuzzing and testing)
- NVD CVE-2024-26166 Entry
Final Thoughts
CVE-2024-26166 is a textbook example of why trusting back-end connections can be dangerous, especially where binary protocols and memory parsing are involved. A simple connection—with no malware files or binaries required—can pop a shell on your system.
If you use OLE DB to talk to SQL Server, patch now, and train users not to connect to unknown servers.
If you’re interested in exploit development, watch the public repos like Zero Day Initiative for future PoCs.
Stay patched—and remember: even "internal-only" data connections can be a risk!
*Share your experiences, or report suspicious SQL traffic in your environment below!*
Timeline
Published on: 03/12/2024 17:15:55 UTC
Last modified on: 03/12/2024 17:46:17 UTC