**Serial number:** AL25-009 **Date:**July 20, 2025Audience——–This Alert is intended for professionals and managers of notified organizations.Purpose——-An Alert is used to raise awareness of a recently identified cyber threat [](#defn-cyber-threat)Cyber threatA threat actor, using the internet, who takes advantage of a known vulnerability in a product for the purposes of exploiting a network and the information the network carries. that may impact cyber information assets, and to provide additional detection [](#defn-detection)DetectionThe monitoring and analyzing of system events in order to identify unauthorized attempts to access system resources. and mitigation advice to recipients. The Canadian Centre for Cyber Security [](#defn-cyber-security)Cyber securityThe protection of digital information, as well as the integrity of the infrastructure housing and transmitting digital information. More specifically, cyber security includes the body of technologies, processes, practices and response and mitigation measures designed to protect networks, computers, programs and data from attack, damage or unauthorized access so as to ensure confidentiality, integrity and availability. (‘Cyber Centre’) is also available to provide additional assistance regarding the content of this Alert to recipients as requested.Details——-On July 19, Microsoft published a customer guidance for a critical SharePoint vulnerability [](#defn-vulnerability)VulnerabilityA flaw or weakness in the design or implementation of an information system or its environment that could be exploited to adversely affect an organization’s assets or operations. CVE-2025-53770 that appears to be affecting all versions of on-premises SharePoint Server ^[Footnote 1](#fn1)^. SharePoint Online in Microsoft 365 is not impacted.The Cyber Centre is aware of exploitation happening in Canada. CVE-2025-53770 involves the deserialization of untrusted data in on-premises Microsoft SharePoint Servers allowing an unauthorised attacker to execute code over a network.A patch is currently not available for this vulnerability. Microsoft is working to release a security update.Suggested actions—————–The Cyber Centre strongly recommends that organizations follow the mitigation and recommendations from Microsoft:* Enable Antimalware Scan Interface (AMSI) integration in SharePoint Server.* Deploy Microsoft Defender Antivirus across all SharePoint servers.* Disconnect the server from the internet if AMSI cannot be enabled.* Deploy Defender for Endpoint to detect and block post-exploit activity.* Follow the mitigation and detections from Microsoft and continually monitor for any released patches.In addition, the Cyber Centre strongly recommends that organizations review and implement the Cyber Centre’s [Top 10 IT Security Actions](/en/guidance/top-10-it-security-actions-protect-internet-connected-networks-and-information-itsm10089) ^[Footnote 2](#fn2)^.If activity matching the content of this alert is discovered, recipients are encouraged to report via the [My Cyber Portal](https://www.cyber.gc.ca/en/incident-management), or email [contact@cyber.gc.ca](mailto:contact@cyber.gc.ca).|| References| ———-||| Footnote 1|| : [Customer guidance for SharePoint vulnerability CVE-2025-53770 -| MSRC Blog -| Microsoft Security Response Center](https://msrc.microsoft.com/blog/2025/07/customer-guidance-for-sharepoint-vulnerability-cve-2025-53770/)|| [Return to footnote 1 referrer](#fn1-rf)||| Footnote 2|| : [Top 10 IT security actions to protect Internet connected networks and information (ITSM.10.089)](/en/guidance/top-10-it-security-actions-protect-internet-connected-networks-and-information-itsm10089)|| [Return to footnote 2 referrer](#fn2-rf)*[IT]: information technology
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