STIGQter: STIG Summary: Microsoft Office 365 ProPlus Security Technical Implementation Guide Version: 3 Release: 5 Benchmark Date: 01 Apr 2026:

When a custom action is executed that uses the Outlook object model, Outlook must automatically deny it.

DISA Rule

SV-223365r961779_rule

Vulnerability Number

V-223365

Group Title

SRG-APP-000488

Rule Version

O365-OU-000020

Severity

CAT II

CCI(s)

• CCI-002460 - Enforce organization-defined actions prior to executing mobile code.

Weight

10

Fix Recommendation

Set the policy value for User Configuration >> Administrative Templates >> Microsoft Outlook 2016 >> Security >> Security Form Settings >> Custom Form Setting >> Set Outlook object model custom actions execution prompt to "Enabled" and select "Automatically Deny".

Check Contents

Verify the policy value for User Configuration >> Administrative Templates >> Microsoft Outlook 2016 >> Security >> Security Form Settings >> Custom Form Security >> Set Outlook object model custom actions execution prompt is set to "Enabled" and "Automatically Deny".

Use the Windows Registry to navigate to the following key:

HKCU\software\policies\microsoft\office\16.0\outlook\security

If the value for "promptoomcustomaction" is set to "REG_DWORD = 0", this is not a finding.

Vulnerability Number

V-223365

Documentable

False

Rule Version

O365-OU-000020

Severity Override Guidance

Verify the policy value for User Configuration >> Administrative Templates >> Microsoft Outlook 2016 >> Security >> Security Form Settings >> Custom Form Security >> Set Outlook object model custom actions execution prompt is set to "Enabled" and "Automatically Deny".

Use the Windows Registry to navigate to the following key:

HKCU\software\policies\microsoft\office\16.0\outlook\security

If the value for "promptoomcustomaction" is set to "REG_DWORD = 0", this is not a finding.

Check Content Reference

M

Target Key

4099