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Update (08/12/2025): CISA has updated this alert to provide clarification on identifying Exchange Servers on an organization’s networks and provided further guidance on running the Microsoft Exchange Health Checker.
Update (08/07/2025): CISA issued Emergency Directive (ED) 25-02: Mitigate Microsoft Exchange Vulnerability in response to CVE-2025-53786.
CISA is aware of the newly disclosed high-severity vulnerability, CVE-2025-53786, that allows a cyber threat actor with administrative access to an on-premise Microsoft Exchange server to escalate privileges by exploiting vulnerable hybrid-joined configurations. This vulnerability, if not addressed, could impact the identity integrity of an organization’s Exchange Online service.
While Microsoft has stated there is no observed exploitation as of the time of this alert’s publication, CISA strongly urges organizations to implement Microsoft’s Exchange Server Hybrid Deployment Elevation of Privilege Vulnerability guidance outlined below, or risk leaving the organization vulnerable to a hybrid cloud and on-premises total domain compromise.
- Organizations should first inventory all Exchange Servers on their networks (organizations should leverage existing visibility tools or publicly available tools, such as NMAP or PowerShell scripts, to accomplish this task).
- If using Exchange hybrid, review Microsoft’s guidance Exchange Server Security Changes for Hybrid Deployments to determine if your Microsoft hybrid deployments are potentially affected and available for a Cumulative Update (CU).
- Install Microsoft’s April 2025 Exchange Server Hotfix Updates on the on-premise Exchange server and follow Microsoft’s configuration instructions Deploy dedicated Exchange hybrid app.
- For organizations using Exchange hybrid (or have previously configured Exchange hybrid but no longer use it), review Microsoft's Service Principal Clean-Up Mode for guidance on resetting the service principal’s
keyCredentials. - Upon completion, run the Microsoft Exchange Health Checker with appropriate permissions to identify the CU level of each Exchange Server identified and to determine if further steps are required.
CISA highly recommends entities disconnect public-facing versions of Exchange Server or SharePoint Server that have reached their end-of-life (EOL) or end-of-service from the internet. For example, SharePoint Server 2013 and earlier versions are EOL and should be discontinued if still in use.
Organizations should review Microsoft’s blog Dedicated Hybrid App: temporary enforcements, new HCW and possible hybrid functionality disruptions for additional guidance as it becomes available.
Disclaimer:
The information in this report is being provided “as is” for informational purposes only. CISA does not endorse any commercial entity, product, company, or service, including any entities, products, or services linked within this document. Any reference to specific commercial entities, products, processes, or services by service mark, trademark, manufacturer, or otherwise, does not constitute or imply endorsement, recommendation, or favoring by CISA.
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