Alert - Vulnerability impacting Microsoft SharePoint Server (CVE-2025-53770) – Update 3

Serial number: AL25-009
Date: July 20, 2025
Updated: July 22, 2025

Audience

This Alert is intended for IT professionals and managers of notified organizations.

Purpose

An Alert is used to raise awareness of a recently identified 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 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 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 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. SharePoint Online in Microsoft 365 is not impacted.

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.

The Cyber Centre is aware of exploitation happening in Canada.

On 21 July, 2025, Microsoft released emergency patches for the following versions of SharePoint:

  • Microsoft SharePoint Server Subscription Edition
  • Microsoft SharePoint Server 2019
  • Microsoft SharePoint Server 2016

Potential indicators of compromise

The following indicators of compromise CompromiseThe intentional or unintentional disclosure of information, which adversely impacts its confidentiality, integrity, or availability. (IoCs) have been shared by the cyber security research communityFootnote 3 as a starting point for compromise detection.

  • Verify the presence of the following file: C:\PROGRA~1\COMMON~1\MICROS~1\WEBSER~1\16\TEMPLATE\LAYOUTS\spinstall0.aspx
    • SHA256:92bb4ddb98eeaf11fc15bb32e71d0a63256a0ed826a03ba293ce3a8bf057a514
  • Monitor IIS logs for POST requests to /_layouts/15/ToolPane.aspx?DisplayMode=Edit&a=/ToolPane.aspx with a HTTP referer of /_layouts/SignOut.aspx
  • Verify network logs for scanning or exploitation attempts from IPs 107.191.58[.]76, 104.238.159[.]149, and 96.9.125[.]147, particularly since July 17, 2025.
  • Check for presence of file hashes that may indicate compromise Footnote 4Footnote 5:
    • SHA256:4a02a72aedc3356d8cb38f01f0e0b9f26ddc5ccb7c0f04a561337cf24aa84030
    • SHA256:b39c14becb62aeb55df7fd55c814afbb0d659687d947d917512fe67973100b70
    • SHA256:fa3a74a6c015c801f5341c02be2cbdfb301c6ed60633d49fc0bc723617741af7
    • SHA256:27c45b8ed7b8a7e5fff473b50c24028bd028a9fe8e25e5cea2bf5e676e531014
    • SHA256:8d3d3f3a17d233bc8562765e61f7314ca7a08130ac0fb153ffd091612920b0f2
    • SHA256:b336f936be13b3d01a8544ea3906193608022b40c28dd8f1f281e361c9b64e93
    • SHA256:f917e0fd57784e40d9a41069f30b2b5cf83db29b52072c308ff030eaf1fcd764

Suggested actions

If your SharePoint Server is accessible via the internet, it is recommended to assess potential security compromises and consider isolating the affected instance until patching and threat hunt exercises are complete.
It is recommended to rotate any credentials and secrets used on impacted servers, including service accounts.

Additionally, the Cyber Centre strongly recommends that organizations follow Microsoft customer guidance for mitigation advice:

  • Use or upgrade to supported versions of on-premises Microsoft SharePoint Server.
  • Apply the latest security updates from Microsoft.
  • Enable Antimalware Scan Interface (AMSI) integration in SharePoint Server.
  • integration was enabled by default in the September 2023 security update for SharePoint Server 2016/2019 and the Version 23H2 feature update for SharePoint Server Subscription Edition Footnote 6.
  • Deploy a compatible AMSI-capable antivirus/antimalware provider across all SharePoint servers.
  • Rotate SharePoint Server ASP.NET machine keys and restart IIS.

Please note that the Cyber Center has identified evidence that AMSI may not consistently offer comprehensive protection against this form of exploitation, as threat actors frequently adapt their methods to evade detection.

In addition, the Cyber Centre strongly recommends that organizations review and implement the Cyber Centre’s Top 10 IT Security Actions Footnote 2.

If activity matching the content of this alert is discovered, recipients are encouraged to report via the My Cyber Portal, or email contact@cyber.gc.ca.

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