security settingsComputer ConfigurationNot configured

Network security: NTLM SSP Security: Minimum session security

Enforces 128-bit encryption and NTLMv2 session security. Value 537133056 enables both requirements. MSPs use this to prevent downgrade attacks on client authentication.

10 May 20264 min —

Policy path: Computer Configuration > Windows Settings > Security Settings > Local Policies > Security Options
Supported on: Windows 10, Windows 11, Windows Server 2016 and later

Enforces 128-bit encryption and NTLMv2 session security. Value 537133056 enables both requirements. MSPs use this to prevent downgrade attacks on client authentication. Security baselines recommend setting it to 537133056.

Description

Network security: NTLM SSP Security: Minimum session security is a Windows Group Policy setting located under Computer Configuration > Windows Settings > Security Settings > Local Policies > Security Options. It applies to the Computer Configuration branch and is classified as a Critical-level policy in the NTLM Authentication category.

Enforces 128-bit encryption and NTLMv2 session security. Value 537133056 enables both requirements. MSPs use this to prevent downgrade attacks on client authentication.

Microsoft sets the default value to 0 while industry security baselines (CIS, NIST, DISA STIG) recommend 537133056.

Under the hood, this policy is enforced through the Windows registry at HKLM\System\CurrentControlSet\Control\Lsa using the value name NTLMMinClientSec. Modifying the value directly through regedit.exe or PowerShell produces the same effect as configuring the GPO, but going through Group Policy is preferred so that the setting is centrally managed and survives reboots, image rebuilds, and policy refresh cycles.

In-depth explanation

This is a critical security control. Misconfiguration creates an exploitable attack path that adversaries actively scan for, and a single overlooked endpoint can compromise the entire fleet. Treat it as a hard baseline requirement rather than an optional tuning knob.

The policy is grouped under NTLM Authentication, which means it is typically applied through a domain-wide GPO linked at the OU level. In a multi-tenant MSP context, scope it through WMI filters or security group filtering rather than linking at the domain root, so that you can roll out progressively (pilot OU → wider rings → all production).

The setting takes effect after the next Group Policy refresh (gpupdate /force for immediate testing, or by default within ~90 minutes for workstations and ~5 minutes on domain controllers). For computer-side policies a reboot may be required; for user-side policies, a sign-off/sign-on cycle is enough.

Use cases

Apply organization-wide hardening of ntlm authentication on all domain-joined Windows endpoints.
Roll out a CIS Benchmark-aligned baseline targeting 'Network security: NTLM SSP Security: Minimum session security' via a dedicated GPO.
Reduce attack surface for accounts that handle privileged credentials or sensitive data.
Standardize the configuration across multiple customer tenants for an MSP-managed fleet.

Security implications

Failing to enforce this policy creates a documented attack path that adversaries actively probe – think Pass-the-Hash, Kerberoasting, NTLM relay, RDP brute-force, LSASS dumping, or token impersonation, depending on the specific control. A single misconfigured endpoint can be enough to pivot to a Domain Admin compromise.

If this policy must remain at default for a legitimate compatibility reason, compensate with a strong detection rule in your EDR/SIEM, isolate the endpoint in its own VLAN, and document the exception with a target remediation date.

How to configure

Open Group Policy Management Console (gpmc.msc) on a domain controller or a workstation with RSAT installed.
Create or edit a GPO linked to the OU containing the target computer configurations. We recommend a dedicated baseline GPO (e.g. SEC – NTLM Authentication) instead of editing Default Domain Policy.
Navigate to Computer Configuration > Windows Settings > Security Settings > Local Policies > Security Options.
Open Network security: NTLM SSP Security: Minimum session security and set it to 537133056.
Click OK and close the editor.
On the target endpoint, run gpupdate /force (or wait for the next refresh cycle), then verify with rsop.msc or gpresult /h report.html.

Direct registry path: HKLM\System\CurrentControlSet\Control\Lsa\NTLMMinClientSec. You can apply the same change with PowerShell:

New-Item -Path 'HKLM\System\CurrentControlSet\Control\Lsa' -Force | Out-Null
Set-ItemProperty -Path 'HKLM\System\CurrentControlSet\Control\Lsa' -Name 'NTLMMinClientSec' -Value <value> -Type DWord

Registry mapping

Registry pathHKLM\System\CurrentControlSet\Control\Lsa

Value nameNTLMMinClientSec

Value typeREG_DWORD

Enabled value537133056

Disabled value0

Frequently asked questions

What does the Network security: NTLM SSP Security: Minimum session security Group Policy do?

Enforces 128-bit encryption and NTLMv2 session security. Value 537133056 enables both requirements. MSPs use this to prevent downgrade attacks on client authentication.

Where do I find this setting in the GPO editor?

Open <code>gpmc.msc</code>, then navigate to <code>Computer Configuration > Windows Settings > Security Settings > Local Policies > Security Options</code> and look for <strong>Network security: NTLM SSP Security: Minimum session security</strong>.

What is the Microsoft default value?

<code>0</code> on a fresh Windows install. Domain-joined machines may inherit a different value if a baseline GPO is already in place.

What value do security baselines recommend?

<code>537133056</code> – aligned with CIS, NIST, and DISA STIG guidance for current Windows versions.

Can I configure this without a GPO?

Yes, by writing to <code>HKLM\System\CurrentControlSet\Control\Lsa\NTLMMinClientSec</code> directly via <code>regedit</code>, PowerShell, or Intune. A GPO is preferred for centrally managed environments because it survives reimaging and is easier to audit.