Microsoft Outlook Elevation of Privilege Vulnerability (CVE-2023-23397)

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Hi All,

There is a Outlook Escalation of Privilege Vulnerability in Outlook. Tony Redmond has explained that very well

Exchange CSS has released a Script to test and mitigate

Exchange On Prem

You need to have an RBAC Admin Role that allows Application Impersonation and assign an Account.

If you don’t have that Role you can create it

New-RoleGroup -Name "CVE-2023-23397-Script" -Roles "ApplicationImpersonation" -Description "Permission to run the CVE-2023-23397 script

You can also create a Throttling Policy

New-ThrottlingPolicy CVE-2023-23397-Script
Set-ThrottlingPolicy "CVE-2023-23397-Script" -EWSMaxConcurrency Unlimited -EWSMaxSubscriptions Unlimited -CPAMaxConcurrency Unlimited -EwsCutoffBalance Unlimited -EwsMaxBurst Unlimited -EwsRechargeRate Unlimited
Set-Mailbox -Identity "" -ThrottlingPolicy "CVE-2023-23397-Script"

Let’s check that Throttling Policy

Get-ThrottlingPolicy -Identity CVE-2023-23397-Script |  fl ews*, cpa*

Download the Script and run it in a Exchange Management Shell

Get-Mailbox | .\CVE-2023-23397.ps1 -Environment Onprem -EWSServerURL http://ExchangeServerName/ews/exchange.asmx

You will need to provide the Credentials of the Account you are using to connect to EWS

No Mailbox with a vulnerability found

Exchange Online

You will need to have the AzureAD PowerShell Module installed

Install-Module AzureAD

Now you need to create the AzureAD Application and you need to have the Global Administrator or an Application Administrator Role.

.\CVE-2023-23397.ps1 -CreateAzureApplication

This will Create an AzureAD Application

And set the Permission “full_access_as_app” which is like Impersonation.

Now you need to connect to Exchange Online


Now you can scan your environement

Get-Mailbox | .\CVE-2023-23397.ps1 -Environment "Online"

You need to Authenticate to register a new Client Secret. That’s why the Script has to wait for 60 Seconds

Every time you run the Script it will register a new Client Secret

I have a lot of Test Mailboxes with no Licenses assigned.

If no vulnerable Items are found the Azure AD Application can be deletet

.\CVE-2023-23397.ps1 -DeleteAzureApplication

Andres Bohren