CISA has issued an emergency directive ordering all Federal Civilian Govt Department (FCEB) companies to mitigate a crucial Microsoft Trade hybrid vulnerability tracked as CVE-2025-53786 by Monday morning at 9:00 AM ET.
Federal Civilian Govt Department (FCEB) companies are non-military companies inside the US government department, together with the Division of Homeland Safety, Division of the Treasury, Division of Power, and Division of Well being and Human Companies.
The flaw tracked as CVE-2025-53786 permits attackers who achieve administrative entry to on-premises Trade servers to maneuver laterally into Microsoft cloud environments, doubtlessly main to finish area compromise.
The vulnerability impacts Microsoft Trade Server 2016, 2019, and the Subscription Version.
In hybrid configurations, Trade On-line and on-premises servers share the identical service principal, which is a shared belief relationship used to authenticate with one another.
An attacker with admin privileges on an on-premise Trade server can doubtlessly forge or manipulate trusted tokens or API calls that the cloud aspect will settle for as reputable. This method permits the attackers to unfold laterally from the native community into the corporate’s cloud atmosphere, doubtlessly compromising the corporate’s whole lively listing and infrastructure.
To make issues worse, Microsoft says cloud-based logging instruments like Microsoft Purview might not log malicious exercise if it originates from on-prem Trade, making it arduous to detect exploitation.
This flaw comes after Microsoft launched steerage and an Trade server hotfix in April 2025 to assist a brand new structure that makes use of a devoted hybrid software, quite than the shared one, as a part of its Safe Future Initiative.
Yesterday, safety researcher Dirk-Jan Mollema of Outsider Safety demonstrated how this shared service principal could possibly be exploited in a post-exploitation assault throughout a Black Hat presentation.
The researcher advised BleepingComputer that he reported the flaw three weeks earlier than the speak, to present Microsoft advance warning. In coordination with the presentation, Microsoft issued the CVE-2025-53786 CVE and steerage on the right way to mitigate it.
“I didn’t initially think about this a vulnerability as a result of the protocol that’s used for these assaults was designed with the options lined throughout the speak, and is simply normally missing necessary safety controls,” Mollema advised BleepingComputer.
“The report describing the chances for attackers was despatched as a heads as much as the MSRC 3 weeks earlier than Black Hat and the disclosure was coordinated with them. Except for this steerage Microsoft additionally mitigated an assault path that would result in full tenant compromise (World Admin) from on-prem Trade.”
The excellent news is that Microsoft Trade clients who beforehand applied the hotfix and the April steerage are already shielded from this new post-exploitation assault.
Nevertheless, those that haven’t applied the mitigations are nonetheless impacted and will set up the hotfix and comply with Microsoft’s directions (doc 1 and doc 2) on deploying the devoted Trade hybrid app.
“Solely making use of the hotfix shouldn’t be adequate on this case, there are guide follow-up actions required emigrate to a devoted service principal,” defined Mollema.
“The urgency from a safety viewpoint depends upon how a lot admins think about isolation between on-prem Trade sources and cloud-hosted sources necessary. Within the outdated setup, Trade hybrid has full entry to all sources in Trade on-line and in SharePoint.”
Mollema additionally reiterated that his method is a post-exploitation assault, which means an attacker already has to have compromised the on-premises atmosphere or the Trade servers, and on this case, have administrator privileges.
Based on CISA’s Emergency Directive 25-02, federal companies should now mitigate the assault by first taking a list of their Trade environments utilizing Microsoft’s Well being Checker script. Any servers which might be now not supported by the April 2025 hotfix, resembling end-of-life Trade variations, should be disconnected.
All remaining servers should be up to date to the newest cumulative updates (CU14 or CU15 for Trade 2019, and CU23 for Trade 2016) and patched with the April hotfix. Afterward, directors should run Microsoft’s ConfigureExchangeHybridApplication.ps1 PowerShell script to modify from the shared to the devoted service principal in Entra ID.
CISA warns that failing to implement these mitigations might lead to hybrid environments being fully compromised.
Businesses should full the technical remediation steps by Monday morning and submit a report back to CISA by 5:00 PM the identical day.
Whereas non-government organizations are usually not required to take motion underneath this directive, CISA urges all organizations to mitigate the assault.
“The dangers related to this Microsoft Trade vulnerability prolong to each group and sector utilizing this atmosphere,” stated CISA Appearing Director Madhu Gottumukkala.
“Whereas federal companies are mandated, we strongly urge all organizations to undertake the actions on this Emergency Directive.”
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