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 that may impact cyber information assets, and to provide additional detection and mitigation advice to recipients. The Canadian Centre for Cyber Security ("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 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 (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.