Microsoft is rolling out stronger security checks for Microsoft Entra Connect to close a long-standing avenue for identity takeover known as hard match abuse or “SyncJacking,” and the changes demand immediate attention from hybrid identity administrators who manage on‑premises Active Directory synchronization. The update introduces enforcement around the onPremises mapping attributes, tighter audit visibility, and controlled recovery paths so that unauthorized remapping attempts are blocked — but the protections also require tenant-side changes, upgrades to the sync client, and careful operational planning to avoid unwanted disruption.
Background
What Microsoft Entra Connect does today
Microsoft Entra Connect (formerly Azure AD Connect) is the synchronization bridge that keeps on‑premises Active Directory and Microsoft Entra ID (Azure AD) in sync. It writes user and group attributes, handles source-of-authority transitions, supports password hash synchronization, and enables hybrid scenarios like single sign‑on and device hybrid join. Because it can change cloud-held attributes based on on‑prem updates, Entra Connect is necessarily powerful — and that power has historically included behaviors (soft match and hard match) that ease migration but can be abused if an attacker gains sufficient on‑prem privileges.The SyncJacking threat in brief
Researchers documented a class of attacks — colloquially called SyncJacking — where an attacker with limited on‑prem privileges can abuse hard match and related matching behaviors to remap a cloud object’s source of authority, overwrite cloud attributes (including password hashes when Password Hash Sync is enabled), and effectively take control of an Entra ID account. Semperis and other identity researchers raised this as a practical threat in 2022 and Microsoft subsequently updated hardening guidance to reduce the attack surface. The recent Entra Connect changes are the next step in formalizing protections inside the sync pipeline itself.What Microsoft is changing
Enforcement of onPremises mapping checks
Microsoft will add enforcement logic in the Entra Connect sync flow to verify onPremises mapping attributes (for example, the onPremisesObjectIdentifier mapping and related fields) before allowing source-of-authority remapping. When the new logic detects suspicious or unexpected remapping attempts it will block the operation and surface an error about a blocked hard match operation. This enforcement is intended to stop silent or forged remaps that were previously exploitable in some scenarios.Expanded auditing and visibility
Audit events will be enhanced to record changes to critical attributes that are commonly used during matching and takeover scenarios — notably changes to onPremisesObjectIdentifier and DirSyncEnabled or other directory synchronization feature flags. This addition improves incident response by giving admins a searchable trail for suspicious remap or takeover attempts.Controlled recovery paths
For legitimate recovery and remediation tasks — for example, when a tenant intentionally shifts an object from cloud‑managed to on‑premises-managed — Microsoft documents that administrators will be able to clear on‑premises mapping attributes in a controlled manner (using Microsoft Graph or Microsoft‑published tooling) and then re-establish mappings securely. Microsoft’s official guidance points to Graph-based updates and a supported PowerShell module (ADSyncTools) for safely clearing on‑prem attributes from cloud-only or migrated users. Administrators must perform these operations carefully and with appropriate roles and permissions.Timeline and version requirements — what’s mandatory
Microsoft’s hardening program for Entra Connect has been rolling out in phases; a back-end service change and new sync behaviors were shipped in recent builds and Microsoft has published minimum supported versions tied to broader service updates. Microsoft has indicated that customers must be on the newer Entra Connect builds to avoid synchronization failures once the back‑end enforcement is active, and the platform docs point to minimum client versions that will be required by 2026. Administrators should treat version 2.5.79.0 (and newer) as the baseline to keep sync working under Microsoft’s updated service model, and plan upgrades well before Microsoft’s enforced deadlines. Note: industry coverage (including a recent Petri piece) reports the specific enforcement of additional hard‑match checks coming into effect in March 2026; Microsoft’s public pages list a variety of related enforcement and deprecation dates through 2026, and tenants must follow their service notifications and the Entra admin center for the precise dates and tenant-level rollout schedule. Treat third‑party reports as early warning and validate dates in your tenant’s message center or service health notifications.Why this matters: concrete attack and defense implications
- Hard match takeover allows the sync engine to change the source of authority for a cloud object to Active Directory. If an attacker can create or control an on‑prem object with the right anchor value, they can take over the cloud account. Blocking unauthorized remapping removes the easy path that made SyncJacking dangerous.
- Adding audits for onPremisesObjectIdentifier and DirSyncEnabled directly improves detection: the attack pattern leaves a small sequence of directory events (e.g., a password change followed by a synchronized update) that defenders can hunt for. The new audit events make that hunting practical from Entra ID logs.
- Recovery and legitimate operations get safer because clearing or resetting mapping attributes will require explicit calls and controlled permissions rather than being implicitly performed by a sync engine operation. Microsoft’s ADSyncTools and Graph-based workflows are the documented ways to carry out these changes.
Immediate actions for administrators (practical checklist)
- Inventory your Entra Connect installations and check the installed version. If you are not on the minimum recommended build(s), schedule an upgrade. Microsoft lists version 2.5.79.0 (or later) as the minimum version required for the recent hardening changes and related backend updates — plan to be compliant well ahead of Microsoft’s enforced cutovers.
- Enable the Entra DirSync feature that blocks cloud object takeover through hard match. Use the supported PowerShell or Graph commands to set the feature flag:
- Example (PowerShell, Entra module):
- Connect with scopes for directory sync administration:
- Connect-Entra -Scopes 'OnPremDirectorySynchronization.ReadWrite.All'
- Enable the feature:
- Set-EntraDirSyncFeature -Features 'BlockCloudObjectTakeoverThroughHardMatch' -Enable $true -TenantId <tenantId> -Force
- You can also manage this setting via the Microsoft Graph directory onPremisesSynchronization resource and Update-MgDirectoryOnPremiseSynchronization for programmatic control.
- Example (PowerShell, Entra module):
- Disable soft match and hard match takeover if you do not need them for migration scenarios. Microsoft recommends disabling these matching behaviors unless they are explicitly required, because they widen the attack surface for remapping and takeover. Test any change in a non‑production tenant or during a maintenance window.
- Harden access to the Entra Connect server(s). Treat the sync server like a domain controller: restrict administrative access to jump boxes or secure admin workstations, enable LAPS for local accounts, and apply strict network controls and monitoring. Attackers who can operate on the sync server have high potential for abuse.
- Enforce MFA and least privilege. Make Multi‑Factor Authentication mandatory for accounts that can affect directory objects, and separate privileged on‑prem and cloud administrative identities to reduce lateral takeover risk.
- Prepare to use Microsoft-supported recovery tools for legitimate remaps. Microsoft documents a supported clearing workflow for on‑prem attributes (ADSyncTools and Graph-based Update User) used when you intentionally convert a synced user to cloud-only or need to reset mapping values. Always back up existing attribute values before performing bulk clears.
- Review audit logs for changes to DirSync feature flags and onPremises mappings. Look for sequences that indicate suspicious takeover attempts — for example, on‑prem password/account updates followed immediately by a cloud update affecting the same object. Enhanced audit events are the primary detection telemetry Microsoft is providing.
How to clear on‑premises mapping attributes safely
Microsoft’s official troubleshooting guidance documents the supported approach for clearing on‑premises attributes from migrated Microsoft Entra ID users. Key points:- Use the ADSyncTools PowerShell module (published on PSGallery) to view and clear on‑premises attributes in bulk or per‑user. The module exposes cmdlets like Get-ADSyncToolsOnPremisesAttribute and Clear-ADSyncToolsOnPremisesAttribute to help with safe rollbacks. Back up attribute values before clearing and perform operations under appropriate admin roles (User Administrator, Hybrid Identity Administrator).
- Microsoft also documents how to update these attributes via Microsoft Graph (Beta) for cloud-only or de‑synced users. Note that some on‑prem properties may be present only in the Graph beta or subject to service restrictions, and behavior can differ by property (for example, onPremisesImmutableId and onPremisesObjectIdentifier have seen different availability and constraints across API versions). Validate API behavior in a test tenant before rolling out large changes.
- Community experience: some administrators have reported intermittent issues when trying to set onPremises immutable identifiers to null via Graph APIs. Those are community reports and appear to vary by tenant, API version, and the exact property being modified. If you encounter failures, rely on the ADSyncTools module and Microsoft support channels rather than scripting mass manual Graph updates in production without testing. Flagging these community reports and filing support cases is prudent.
Operational impacts and risks
False positives and blocked legitimate operations
By design, a hardening rule that blocks remaps will also block some legitimate scenarios if they aren't executed using the documented recovery and migration processes. For example, turning on BlockCloudObjectTakeoverThroughHardMatch while DirSync is disabled or during staged migrations could prevent intended re‑association of objects. Test and document your migration and disaster recovery playbooks now so you can move quickly when legitimate clearing or reattachment is required.API compatibility and admin friction
The Graph API property surface for on‑prem attributes has evolved (and some onPremises* properties have been available in beta but not v1.0). Expect some differences when you try to automate attribute clearing with scripts that call v1.0 endpoints. Use ADSyncTools or follow Microsoft’s documented Graph Beta examples for now, and track Graph changelogs for promotion of properties to v1.0. Always test scripts in non‑production tenants.Timing and service deadlines
Microsoft’s documentation shows multiple 2025–2026 enforcement horizons for related Entra/Entra Connect behaviors (autoupgrade, support for certain authentication modes, and the minimum Entra Connect client version for backend changes). Where third‑party outlets report a March 2026 rollout for specific hard match enforcement, verify the tenant‑level schedule in the Entra admin center and Microsoft Message Center; Microsoft often staggers enforcement regionally and by tenant. Do not assume a single global date without tenant confirmation.Recommended priority roadmap (30/60/90 day plan)
- Day 0–30 (Immediate)
- Inventory Entra Connect instances and document installed versions and patch levels.
- Subscribe to tenant Message Center alerts and Microsoft 365 Service Health notifications for Entra Connect and directory sync updates.
- Run the Get-EntraDirSyncFeature or Get-MgDirectoryOnPremiseSynchronization cmdlets to view current DirSync features and flags.
- Day 30–60 (Short term)
- Test upgrading Entra Connect to the recommended minimum version in a lab or staging environment; validate group writeback, attribute flow, and custom sync rules.
- Enable BlockCloudObjectTakeoverThroughHardMatch in a controlled environment and exercise your recovery procedures (clear mapping attributes via ADSyncTools on a test user).
- Day 60–90 (Operationalize)
- Update runbooks and incident response playbooks to include auditing checks for onPremisesObjectIdentifier changes and steps to use ADSyncTools or Graph to remediate true positives.
- Enforce MFA on all privileged accounts; restrict access to the sync server and validate just‑in‑time or just‑enough‑administration controls.
Practical examples and commands
- Enable the hard-match block feature (PowerShell / Entra module example):
- Connect-Entra -Scopes 'OnPremDirectorySynchronization.ReadWrite.All'
- $tenantID = (Get-EntraContext).TenantId
- Set-EntraDirSyncFeature -Features 'BlockCloudObjectTakeoverThroughHardMatch' -Enable $true -TenantId $tenantID -Force
- Use Get-EntraDirSyncFeature to verify the setting.
- View and clear on‑prem attributes using ADSyncTools (example):
- Install-Module ADSyncTools
- Import-Module ADSyncTools
- Get-ADSyncToolsOnPremisesAttribute | Export-Csv backupOnpremisesAttributes.csv
- Get-ADSyncToolsOnPremisesAttribute -Identity 'user@contoso.com' | Clear-ADSyncToolsOnPremisesAttribute -All
- Always back up before clearing and test in non‑production.
Final analysis — strengths, limitations, and what to watch
Microsoft’s hardening of Entra Connect addresses a meaningful real‑world risk: SyncJacking and hard‑match abuse have proven to be an attractive path to account takeover in well‑documented research. Embedding enforcement logic into the sync engine and surfacing clearer audit events is a strong defensive move: it reduces the reliance on operator discipline alone and gives defenders better telemetry to detect takeover attempts. The option to use controlled recovery flows (Graph/ADSyncTools) balances security with operational needs. However, there are important operational caveats. The changes introduce the potential for blocking legitimate synchronization/repair operations if tenants are not prepared or if runbooks haven’t been updated. API behavior around on‑premises attributes (particularly for newer properties) has been evolving; administrators have reported intermittent Graph behaviors and differences between Beta and v1.0 endpoints. Those operational frictions increase the chance of error during migration and remediation workflows, so test first, back up always, and coordinate with Microsoft support when needed. Finally, public reporting (including vendor blogs and trade publications) is useful for early warning, but administrators must verify specific enforcement dates and tenant rollouts using the Microsoft Entra admin center and Message Center — Microsoft’s published deadlines for related Entra/Entra Connect changes extend across 2025–2026 and may be staged. Treat outside articles as actionable alerts but validate with Microsoft’s official tenant notifications before making irreversible changes.Conclusion
The Entra Connect hardening program is a necessary upgrade to raise the bar against hard‑match takeover and SyncJacking. Organizations that operate hybrid identity must treat this change as both a security opportunity and an operational requirement: upgrade Entra Connect to supported versions, enable the BlockCloudObjectTakeoverThroughHardMatch and other recommended DirSync features, harden access to sync infrastructure, validate remediation playbooks (using ADSyncTools or sanctioned Graph operations), and tune detection logic to hunt for suspicious DirSync events. Done carefully, these steps will significantly reduce one of the more subtle routes to account compromise in hybrid environments; done poorly, they can interrupt sync and complicate migration tasks — which is why testing, backups, and staged rollouts are essential.Source: Petri IT Knowledgebase Microsoft Entra Connect Security Hardening to Block Account Hijacks
