ANSSI-FR / DFIR-O365RC

Table of contents:

1. Module description
2. Installation and pre-requisites
3. Roles and license requirements
4. Functions included in the module
5. Files generated

DFIR-O365RC was presented at the SSTIC 2021 (Symposium sur la sécurité des technologies de l'information et des communications). Slides and a recording of the presentation, in french language, are available here.

Module description

The DFIR-O365RC PowerShell module is a set of functions that allow the DFIR analyst to collect logs relevant for Office 365 Business Email Compromise and Azure investigations.

The logs are generated in JSON format and retrieved from two main data sources:

• Office 365 Unified Audit Logs.
• Azure AD sign-ins logs and audit logs.

The two data sources can be queried from different endpoints:

DFIR-O365RC is a forensic tool, its aim is not to monitor in real time your Office 365 infrastructure: Please use the Office 365 Management API if you want to analyze data in real time with a SIEM.

DFIR-O365RC will fetch data from:

• Azure AD Logs using the MS Graph API because performance is good, history is 30 days and it works on PowerShell Core.
• Unified Audit Logs using Exchange online PowerShell despite poor performance, history is 90 days and it works on PowerShell Core.

If you are investigating Exchange Online malicious activity, the Search-O365 function will also fetch the Mailbox Audit Log, using Exchange Online PowerShell.

In case you are also investigating other Azure resources (IaaS, PaaS...) DFIR-O365RC can also fetch data from Azure Activity logs using the Azure Monitor RESTAPI. History is 90 days and it works on PowerShell Core. The Azure Activity log is primarily for activities that occur in Azure Resource Manager.

Additionally you can dump Azure DevOps Activity logs using the Azure DevOps services RESTAPI. History is 90 days and it works on PowerShell Core.

Because all functions can run on PowerShell Core, DFIR-O365RC works also on Linux or Mac, as long as you have have a browser in order to use device login.

Installation and pre-requisites

Manual Installation.

Clone the DFIR-O365RC repository. The tool works on PowerShell Desktop and PowerShell Core.

DFIR-O365 uses Jason Thompson's MSAL.PS and Boe Prox's PoshRSJob modules. To install them run the following commands:

Install-Module -Name MSAL.PS -RequiredVersion '4.21.0.1'
Install-Module -Name PoshRSJob -RequiredVersion '1.7.4.4'

If MSAL.PS module installation fails with the following message:

WARNING: The specified module ‘MSAL.PS’ with PowerShellGetFormatVersion ‘2.0’ is not supported by the current version of PowerShellGet. Get the latest version of the PowerShellGet module to install this module, ‘MSAL.PS’.

Update PowerShellGet with the following commands:

Install-PackageProvider Nuget -Force
Install-Module -Name PowerShellGet -Force

Once both modules are installed, launch a PowerShell prompt and locate your Powershell modules path with the following command:

PS> $env:PSModulePath

Copy the DFIR-O365RC directory in one of your modules path, for example on Windows:

• %USERPROFILE%\Documents\WindowsPowerShell\Modules
• %ProgramFiles%\WindowsPowerShell\Modules
• %SYSTEMROOT%\system32\WindowsPowerShell\v1.0\Modules

Modules path examples on Linux:

• /home/%USERNAME%/.local/share/powershell/Modules
• /usr/local/share/powershell/Modules
• /opt/microsoft/powershell/7/Modules

On PowerShell Core, the installation of the WSMan client might also be required:

Install-Module PSWSMan
Install-WSMan

The DFIR-O365RC module is installed, restart the PowerShell prompt and load the module:

PS> Import-module DFIR-O365RC

Use Docker to run DFIR-O365RC.

Use docker-compose to build the image, run the container and mount a volume to retrieve logs:

sudo docker-compose run dfir-o365rc

The module is ready to use:

PowerShell 7.1.4
Copyright (c) Microsoft Corporation.

https://aka.ms/powershell
Type 'help' to get help.
DFIR-O365RC: PowerShell module for Office 365 and Azure log collection
https://github.com/ANSSI-FR/DFIR-O365RC
Loading personal and system profiles took 854ms.
PS /mnt/host/output>

Roles and license requirements

The user launching the tool should have the following roles:

• Microsoft 365 role (portal.microsoft.com): Global reader
• Exchange Online role (outlook.office365.com/ecp): View-Only Audit Logs

In order to retrieve Azure AD sign-ins logs with the MS Graph API you need at least one user with an Azure AD Premium P1 license. This license can be purchased at additional cost for a single user and is sometimes included in some license plans such as the Microsoft 365 Business Premium for small and medium-sized businesses.

If you need to retrieve also the Azure Activity logs you need the Log Analytics Reader role for the Azure subscription you are dumping the logs from.

Finally if you need to collect the Azure DevOps Activity logs you need to grant the Auditing\View audit log permission to the user in the Azure DevOps organization you are dumping the logs from.

Functions included in the module

The module has 9 functions:

When querying Unified audit logs you are limited to 3 concurrent Exchange Online Powershell sessions. DFIR-O365RC will try to use all available sessions, please close any existing session before launching the log collection.

Each function as a comment based help which you can invoke with the get-help cmdlet.

#Display comment based help
PS> Get-help Get-O365Full
#Display comment based help with examples
PS> Get-help Get-O365Full -examples

Each function takes as a parameter a start date and an end date.

In order to retrieve Azure AD audit logs, sign-ins logs from the past 30 days and tenant information launch the following command:

$enddate = get-date
$startdate = $enddate.adddays(-30)
Get-AADLogs -startdate $startdate -enddate $enddate

In order to retrieve enriched Azure AD audit logs related to Azure applications and service principals from the past 30 days launch the following command:

$enddate = get-date
$startdate = $enddate.adddays(-30)
Get-AADApps -startdate $startdate -enddate $enddate

In order to retrieve enriched Azure AD audit logs related to Azure AD joined or registered devices from the past 30 days launch the following command:

$enddate = get-date
$startdate = $enddate.adddays(-30)
Get-AADDevices -startdate $startdate -enddate $enddate

In order to retrieve all unified audit logs considered of interest from the past 30 days, except those related to Azure AD, which were already retrieved by the first command, launch:

$enddate = get-date
$startdate = $enddate.adddays(-30)
Get-O365Light -startdate $startdate -enddate $enddate -Operationsset "AllbutAzureAD"

In order to retrieve all unified audit logs considered of interest in a time window between -90 days and -30 days from now launch the following command:

$enddate = (get-date).adddays(-30)
$startdate = (get-date).adddays(-90)
Get-O365Light -StartDate $startdate -Enddate $enddate -Operationsset All

If mailbox audit is enabled and you want also to retrieve Mailboxlogin operations you can use the dedicated switch, on large tenants beware of a 50.000 events per day limit retrieval.

Get-O365Light -StartDate $startdate -Enddate $enddate -Operationsset All -MailboxLogin $true

If there are users with Enterprise 5 licenses or if there is a Microsoft Defender for Office 365 Plan you can retrieve Microsoft Defender related logs with the following command:

$enddate = get-date
$startdate = $enddate.adddays(-90)
Get-DefenderforO365 -StartDate $startdate -Enddate $enddate

To retrieve all Exchange Online related records from the unified audit logs between Christmas eve and Boxing day, beware that performance might be poor on a large tenant:

$startdate = get-date "12/24/2020"
$enddate = get-date "12/26/2020"
Get-O365Full -StartDate $startdate -Enddate $enddate -RecordSet ExchangeOnly

You can use the search function to look for IP addresses, activity related to specific users or perfrom a freetext search in the unified audit logs:

$enddate = get-date
$startdate = $enddate.adddays(-90)
#Retrieve events using the Exchange online Powershell AppId
Search-O365 -StartDate $startdate -Enddate $enddate -FreeText "a0c73c16-a7e3-4564-9a95-2bdf47383716"

#Search for events related to the X.X.X.X and Y.Y.Y.Y IP adresses, argument is a string separated by comas.
Search-O365 -StartDate $startdate -Enddate $enddate -IPAddresses "X.X.X.X,Y.Y.Y.Y"

#Retrieve events related to users [email protected] and [email protected] , argument is a system.array object
Search-O365 -StartDate $startdate -Enddate $enddate -UserIds "[email protected]", "[email protected]"

When searching for specific users, Search-O365 will also search in the Mailbox Audit Log. Because depending on the user's licence level and settings, audit logs might not be present in the unified audit logs.

To retrieve all Azure Activity logs the account has access to, launch the following command, available subscriptions will be displayed:

$enddate = get-date
$startdate = $enddate.adddays(-90)
Get-AzRMActivityLogs -StartDate $startdate -Enddate $enddate

To retrieve all Azure DevOps Activity logs the account has access to, launch the following command, available Azure DevOps organizations will be displayed:

$enddate = get-date
$startdate = $enddate.adddays(-90)
Get-AzDevOpsActivityLogs -StartDate $startdate -Enddate $enddate

When using PowerShell Core the authentication process will require a device code, you will need to use the devicecode parameter and launch your browser, open the https://microsoft.com/devicelogin URL and enter the code provided by the following message:

PS> Get-O365Light -StartDate $startdate -Enddate $enddate -DeviceCode:$true
To sign in, use a web browser to open the page https://microsoft.com/devicelogin and enter the code XXXXXXXX to authenticate.

Files generated

All files generated are in JSON format.

• Get-AADApps creates a file named AADApps_%FQDN%.json in the azure_ad_apps folder where FQDN is the domain name part of the account used to collect the logs.
• Get-AADDevices creates a file named AADDevices_%FQDN%.json in the azure_ad_devices folder.
• Get-AADLogs creates folders named after the current date using the YYYY-MM-DD format in the azure_ad_signin folder, in each directory a file called AADSigninLog_%FQDN%_YYYY-MM-DD_HH-00-00.json is created for Azure AD sign-ins logs. A folder azure_ad_audit is also created and results are dumped in files named AADAuditLog_%FQDN%_YYYY-MM-DD.json for Azure AD audit logs. Finally a folder called azure_ad_tenant is created and the general tenant information written in a file named AADTenant_%FQDN%.json.
• Get-AzRMActivityLogs creates folders named after the current date using the YYYY-MM-DD format in the azure_rm_activity folder, in each directory a file called AzRM_%FQDN%_%SubscriptionID%_YYYY-MM-DD_HH-00-00.json is created where %SubscriptionID% is the Azure subscription ID. A folder called azure_rm_subscriptions is created and each subscription information written in a file named AzRMsubscriptions_%FQDN%.json.
• Get-AzDevOpsActivityLogs creates folders named after the current date using the YYYY-MM-DD format in the azure_DevOps_activity folder, in each directory a file called AzDevOps_%FQDN%_%DevOpsOrganizationname%_YYYY-MM-DD_HH-00-00.json is created where %DevOpsOrganizationname% is the Azure DevOps organization name. A folder called azure_DevOps_orgs is created and each azure DevOps organization information written in a file named *AzdevopsOrgs_%FQDN%.json.
• Get-O365Full creates folders named after the current date using the YYYY-MM-DD format in the O365_unified_audit_logs, in each directory a file called UnifiedAuditLog_%FQDN%_YYYY-MM-DD_HH-00-00.json is created.
• Get-O365Light creates folders named after the current date using the YYYY-MM-DD format in the O365_unified_audit_logs, in each directory a file called UnifiedAuditLog_%FQDN%_YYYY-MM-DD.json is created.
• Get-DefenderforO365 creates folders named after the current date using the YYYY-MM-DD format in the O365_unified_audit_logs, in each directory a file called UnifiedAuditLog_%FQDN%_YYYY-MM-DD_DefenderforO365.json is created.
• Search-O365 creates folders named after the current date using the YYYY-MM-DD format in the O365_unified_audit_logs, in each directory a file called UnifiedAuditLog_%FQDN%YYYY-MM-DD%searchtype%.json is created, where searchtype can have the values "Freetext", "IPAddresses" or "UserIds". MailboxAuditLog_%FQDN%_YYYY-MM-DD_UserIds.json files can also be created when investigating activity from users.

Launching the various functions will generate a similar directory structure:

DFIR-O365_Logs
│   Get-AADApps.log
│   Get-AADDevices.log
│   Get-AADLogs.log
|   Get-AzRMActivityLogs
│   Get-DefenderforO365.log
│   Get-O365Light.log    
│   Search-O365.log
└───azure_ad_apps
│    │   AADApps_%FQDN%.json
└───azure_ad_audit
│    │   AADAuditLog_%FQDN%_YYYY-MM-DD.json
│    │   ...
└───azure_ad_devices
│    │   AADDevices_%FQDN%.json 
└───azure_ad_signin
│   │
│   └───YYYY-MM-DD
│       │   AADSigninLog_%FQDN%_YYYY-MM-DD_HH-00-00.json
│       │   ...
└───azure_ad_tenant
│    │   AADTenant_%FQDN%.json
└───azure_rm_activity
│   │
│   └───YYYY-MM-DD
│       │   AzRM_%FQDN%_%SubscriptionID%_YYYY-MM-DD_HH-00-00.json
│       │   ...
└───azure_rm_subscriptions
│    │   AzRMsubscriptions_%FQDN%.json
└───azure_DevOps_activity
│   │
│   └───YYYY-MM-DD
│       │   AzDevOps_%FQDN%_%DevOpsOrganisationname%_YYYY-MM-DD_HH-00-00.json
│       │   ...
└───azure_DevOps_orgs
│    │   AzdevopsOrgs_%FQDN%.json
└───O365_unified_audit_logs
│   │
│   └───YYYY-MM-DD
│       │   UnifiedAuditLog_%FDQN%_YYYY-MM-DD.json
│       │   UnifiedAuditLog_%FQDN%_YYYY-MM-DD_freetext.json
│       │   MailboxAuditLog_%FQDN%_YYYY-MM-DD_UserIds.json
│       │   UnifiedAuditLog_%FQDN%_YYYY-MM-DD_DefenderforO365.json
│       │   UnifiedAuditLog_%FQDN%_YYYY-MM-DD_HH-00-00.json
│       │   ...