Introduction
An attacker can become Global Administrator of your Microsoft 365 tenant by exploiting a vulnerability in your hybrid identity synchronization. This technique, called SyncJacking or hard-match abuse, allows compromising privileged cloud accounts via your on-premises Active Directory.
Microsoft is deploying critical application changes in March 2026 to block this attack. Without action on your part, your hybrid infrastructure remains vulnerable.
Critical Impact
This vulnerability affects all tenants using Entra Connect Sync or Cloud Sync with privileged cloud-only accounts.
Technical Anatomy of the SyncJacking Attack
Hard-match Principle
The hard-match is the mechanism that allows associating an on-premises AD object to an existing Entra ID object during the first synchronization. This association is performed via three attributes:
- userPrincipalName (UPN)
- mail or proxyAddresses
- ImmutableId (mapped from objectGUID or ms-DS-ConsistencyGuid)
Attack Vector
The exploitation follows this sequence:
Target Reconnaissance
The attacker identifies a privileged cloud-only account (ex: BreakGlass@contoso.onmicrosoft.com) without OnPremisesObjectIdentifier attribute.
Creation of Malicious Object
Creation of an on-premises AD user with corresponding attributes:
1# DO NOT EXECUTE - Attack Example2New-ADUser -Name "FakeBreakGlass" `3 -UserPrincipalName "BreakGlass@contoso.onmicrosoft.com" `4 -EmailAddress "BreakGlass@contoso.onmicrosoft.com"Synchronization and Overwrite
During the next synchronization cycle, Entra Connect performs a hard-match and overwrites the cloud object with properties of the on-premises object, including the password.
Exploit Architecture
1graph LR2 A[AD On-Premises] -->|Sync| B[Entra Connect]3 B -->|Hard-Match| C[Entra ID]4 D[Privileged Cloud Account] -.->|Overwritten| C5 E[Attacker] -->|Controls| AMicrosoft Application Changes - March 2026
OnPremisesObjectIdentifier Behavior Modifications
| Behavior | Before March 2026 | After March 2026 |
|---|---|---|
| Hard-match on cloud-only | Silently Allowed | Blocked with explicit error |
| OnPremisesObjectIdentifier Validation | Post-synchronization | Pre-synchronization |
| Logging of attempts | Minimal | Detailed with correlation ID |
| Recovery API | Not available | Dedicated Graph endpoint |
New Error Codes
1{2 "error": {3 "code": "HardMatchBlockedOnCloudOnlyAccount",4 "message": "Hard-match attempt blocked on cloud-only privileged account",5 "details": {6 "targetObjectId": "guid",7 "sourceAnchor": "base64",8 "correlationId": "guid"9 }10 }11}Vulnerability Audit: Identify Your Exposure
Complete PowerShell Audit Script
1# Connection to required modules2Connect-MgGraph -Scopes "User.Read.All", "Directory.Read.All"3Import-Module ActiveDirectory4 5# Audit function for at-risk accounts6function Test-SyncJackingVulnerability {7 param(8 [string]$DomainSuffix = "onmicrosoft.com"9 )10 11 # 1. Retrieve all privileged cloud-only accounts12 $privilegedRoles = @(13 "62e90394-69f5-4237-9190-012177145e10", # Global Administrator14 "e8611ab8-c189-46e8-94e1-60213ab1f814", # Privileged Role Administrator15 "158c047a-c907-4556-b7ef-446551a6b5f7" # Cloud Application Administrator16 )17 18 $vulnerableAccounts = @()19 20 foreach ($roleId in $privilegedRoles) {21 $roleMembers = Get-MgDirectoryRoleMember -DirectoryRoleId $roleId22 23 foreach ($member in $roleMembers) {24 $user = Get-MgUser -UserId $member.Id -Property Id,UserPrincipalName,OnPremisesSyncEnabled,OnPremisesImmutableId,OnPremisesDistinguishedName25 26 # Check if it is a cloud-only account27 if (-not $user.OnPremisesSyncEnabled -and $user.UserPrincipalName -like "*$DomainSuffix") {28 $vulnerableAccounts += [PSCustomObject]@{29 UserPrincipalName = $user.UserPrincipalName30 ObjectId = $user.Id31 HasImmutableId = [bool]$user.OnPremisesImmutableId32 RiskLevel = if (-not $user.OnPremisesImmutableId) { "CRITICAL" } else { "MEDIUM" }33 }34 }35 }36 }37 38 # 2. Check for corresponding AD objects39 foreach ($account in $vulnerableAccounts) {40 $upn = $account.UserPrincipalName41 $adUser = Get-ADUser -Filter "UserPrincipalName -eq '$upn'" -ErrorAction SilentlyContinue42 43 if ($adUser) {44 $account | Add-Member -NotePropertyName "ADObjectFound" -NotePropertyValue $true45 $account.RiskLevel = "CRITICAL - IMMEDIATE ACTION REQUIRED"46 }47 }48 49 return $vulnerableAccounts50}51 52# Execute audit53$results = Test-SyncJackingVulnerability54$results | Format-Table -AutoSizeValidation via Microsoft Graph API
1# Graph query to identify accounts without OnPremisesObjectIdentifier2$uri = "https://graph.microsoft.com/v1.0/users?`$filter=accountEnabled eq true and onPremisesSyncEnabled ne true&`$select=id,userPrincipalName,onPremisesImmutableId,createdDateTime&`$top=999"3 4$headers = @{5 Authorization = "Bearer $accessToken"6}7 8$response = Invoke-RestMethod -Uri $uri -Headers $headers -Method Get9$cloudOnlyUsers = $response.value | Where-Object { -not $_.onPremisesImmutableId }Analysis of Entra Connect Logs
1# Search in synchronization logs2$syncLogs = Get-EventLog -LogName "Application" -Source "Directory Synchronization" -After (Get-Date).AddDays(-7)3$hardMatchEvents = $syncLogs | Where-Object { $_.Message -match "hard.*match|immutableid.*conflict" }Technical Remediation Plan
Phase 1: Immediate Protection
Block Unauthorized Hard-Matches
Enable preventive protection via PowerShell:
1# Entra Connect Configuration2Set-ADSyncScheduler -SyncCycleEnabled $false3 4# Add filtering rules5$rule = New-ADSyncRule `6 -Name "Block CloudOnly HardMatch" `7 -Direction Inbound `8 -Precedence 50 `9 -SourceObjectType user `10 -TargetObjectType person `11 -LinkType Join `12 -Disabled $falseImplement Real-Time Monitoring
Deploy an Azure Monitor alert:
1{2 "properties": {3 "severity": "Sev0",4 "enabled": true,5 "scopes": ["/subscriptions/{subscription-id}/resourceGroups/{resource-group}/providers/Microsoft.OperationalInsights/workspaces/{workspace}"],6 "evaluationFrequency": "PT5M",7 "windowSize": "PT5M",8 "criteria": {9 "allOf": [{10 "query": "AuditLogs | where OperationName == 'Update user' and TargetResources contains 'onPremisesImmutableId'",11 "timeAggregation": "Count",12 "operator": "GreaterThan",13 "threshold": 014 }]15 }16 }17}Update Entra Connect
Verify and update your version:
1# Minimum required version: 2.2.8.02$currentVersion = (Get-ADSyncGlobalSettings).Parameters | Where-Object {$_.Name -eq "Microsoft.Synchronize.ServerConfigurationVersion"}3 4if ([version]$currentVersion.Value -lt [version]"2.2.8.0") {5 Write-Warning "Critical update required!"6 # Download from https://aka.ms/AADConnectDownload7}Phase 2: Advanced Configuration
Recommended Configuration
Enable certificate-based authentication for the Entra Connect service account to prevent password compromise.
1# Configure connector with certificate2$cert = New-SelfSignedCertificate -Subject "CN=EntraConnectSync" -CertStoreLocation "Cert:\LocalMachine\My" -KeyExportPolicy Exportable -KeySpec Signature -KeyLength 2048 -HashAlgorithm SHA2563 4# Export and configuration5$certPassword = ConvertTo-SecureString -String "ComplexP@ssw0rd!" -Force -AsPlainText6Export-PfxCertificate -Cert $cert -FilePath "C:\EntraConnect\sync-cert.pfx" -Password $certPasswordComplete Validation Checklist
Recommended Weekly Validation
This checklist should be executed weekly until the complete application of March 2026 changes.
- [ ] Audit of privileged cloud-only accounts: Execute the PowerShell audit script
- [ ] OnPremisesObjectIdentifier verification: Confirm that all critical accounts have an immutable identifier
- [ ] Analysis of synchronization logs: Search for suspicious hard-match attempts
- [ ] Entra Connect version: Verify version 2.2.8.0 or higher
- [ ] Synchronization rules: Validate exclusions for critical UPNs
- [ ] Active monitoring: Confirm Azure Monitor alerts are operational
- [ ] Identifier backup: Back up OnPremisesImmutableId of privileged accounts
- [ ] Recovery test: Validate post-compromise restoration procedure
- [ ] Attribute filtering: Verify that userPrincipalName is not synchronized for onmicrosoft.com domains
- [ ] AD permissions audit: Limit who can create objects in synchronized OUs
Frequent Errors and Solutions
1. Synchronization of BreakGlass Accounts
Critical Error
Never include emergency accounts in the synchronization scope.
1# Correct exclusion2Set-ADSyncSchedulerConnectorOverride -ConnectorIdentifier $connectorId -FullImportRequired $true -FullSyncRequired $true3Add-ADSyncAADCompanyFeature -ForcePasswordSync $false -ForceUserPrincipalNameSync $false2. Absence of Monitoring for Synchronization Failures
1# Automated monitoring script2$webhook = "https://outlook.office.com/webhook/..."3$errors = Get-ADSyncRunStepResult -RunHistoryId (Get-ADSyncRunProfileResult)[0].RunHistoryId | Where-Object {$_.StepResult -ne "Success"}4 5if ($errors) {6 Invoke-RestMethod -Uri $webhook -Method Post -Body ($errors | ConvertTo-Json)7}3. Incorrect sourceAnchor Configuration
1# Validate sourceAnchor2$connector = Get-ADSyncConnector | Where-Object {$_.Type -eq "AD"}3if ($connector.Parameters['UserSourceAnchor'] -ne 'ms-DS-ConsistencyGuid') {4 Write-Error "Unsecured sourceAnchor configuration detected"5}4. Excessive AD Permissions
1# Audit permissions2$syncAccount = "MSOL_[identifier]"3$permissions = Get-ACL "AD:\CN=Users,DC=contoso,DC=com" | Select-Object -ExpandProperty Access | Where-Object {$_.IdentityReference -match $syncAccount}5. Absence of Centralized Logs
1// Log Analytics configuration for Entra Connect2resource workspace 'Microsoft.OperationalInsights/workspaces@2021-12-01-preview' = {3 name: 'EntraConnectMonitoring'4 location: resourceGroup().location5 properties: {6 retentionInDays: 907 features: {8 enableLogAccessUsingOnlyResourcePermissions: true9 }10 }11}30/60/90 Day Implementation Plan
Days 1-30: Assessment and Emergency Protection
- Week 1: Complete audit with identification of vulnerable accounts
- Week 2: Implementation of synchronization exclusions
- Week 3: Deployment of monitoring and alerts
- Week 4: Validation testing and documentation
Days 31-60: Hardening and Automation
- Migration to certificate-based authentication
- Automation of daily audits
- Training of teams on new processes
- Implementation of least privilege principle in AD
Days 61-90: Preparation for March 2026 Changes
- Testing in pre-production environment
- Validation with Microsoft Support
- Documented rollback plan
- Post-compromise recovery exercises
Critical Deadline
Application changes will be effective in March 2026. No extensions will be granted.
Resources and Documentation
Official Microsoft Links
- Entra Connect Security Documentation
- MSRC Security Advisory
- Entra Connect Hardening Guide
- Graph API for Identity Management
Additional PowerShell Scripts
1# GitHub repository with remediation scripts2# git clone https://github.com/Microsoft/EntraConnectSecurityTechnical Glossary
- Hard-match: Process of associating AD and Entra ID objects based on common attributes
- OnPremisesObjectIdentifier: Entra ID attribute storing the GUID of the source AD object
- SourceAnchor: Immutable attribute used for permanent object association
- ImmutableId: Base64 identifier of the sourceAnchor in Entra ID
- SyncJacking: Exploitation technique using hard-match to compromise cloud accounts
Immediate Action Required
Start Your Audit Today
Every day of delay increases your exposure. Run the audit script now and implement emergency protections within 48 hours.
Securing your hybrid identity infrastructure is not optional. The March 2026 changes will permanently block this vulnerability, but only if your configuration is correct. Validate, protect, and prepare yourself now.



