TMA-OFFICE-2.2.4.7.2.1.3

Ensure 'Don't allow Dynamic Data Exchange (DDE) server lookup in Excel' is set to 'Enabled'

HighLevel 1Automatedoffice

Description

This policy setting allows controls whether Dynamic Data Exchange (DDE) server lookup is allowed. The DDE protocol is a set of messages and guidelines. It sends messages between applications that share data and uses shared memory to exchange data between applications. Rationale: In an email attack scenario, an attacker could leverage the DDE protocol by sending a specially crafted file to the user and then convincing the user to open the file, typically by way of an enticement in an email. User setting: the audit checks HKEY_USERS\<SID>\SOFTWARE\Policies\Microsoft\office\16.0\excel\security\externalcontent:disableddeserverlookup (REG_DWORD) in every loaded user hive (S-1-5-21-*) and is compliant when each holds 1. It prints 'no-user-hive-loaded' (FAIL) when no user profile is loaded, so scan while users are logged on.

How it is checked

Audit method: Windows registry

registry

$sids = @(Get-ChildItem -Path 'Registry::HKEY_USERS' -ErrorAction SilentlyContinue | Where-Object { $_.PSChildName -match '^S-1-5-21-\d+-\d+-\d+-\d+$' } | ForEach-Object { $_.PSChildName }); if ($sids.Count -eq 0) { 'no-user-hive-loaded' } else { $bad = @(); foreach ($s in $sids) { $v = (Get-ItemProperty -Path ('Registry::HKEY_USERS\' + $s + '\SOFTWARE\Policies\Microsoft\office\16.0\excel\security\externalcontent') -Name 'disableddeserverlookup' -ErrorAction SilentlyContinue).'disableddeserverlookup'; if (-not ($null -ne $v -and @(1) -contains [int64]$v)) { $bad += $s + ':disableddeserverlookup=' + $v } }; if ($bad.Count -eq 0) { 'compliant' } else { 'non-compliant: ' + ($bad -join ', ') } }

Expected output: compliant

How it is fixed

Fix method: Guidance or infrastructure patch

Configure through Group Policy (User Configuration): User Configuration\Administrative Templates\Microsoft Excel 2016\Excel Options\Security\Trust Center\External Content\Don’t allow Dynamic Data Exchange (DDE) server lookup in Excel = Enabled

Properties

Operating systems: Any
Tags: officeproductivitycis-l1
Reference: CIS Microsoft Office Enterprise Benchmark v2.0.0 - 2.2.4.7.2.1.3 Ensure 'Don't allow Dynamic Data Exchange (DDE) server lookup in Excel' is set to 'Enabled'

Check this host

Run this on a machine you are allowed to audit. The scan is read-only.

shell

tmaegis scan --target office