On July 18, 2025, Sophos MDR (Managed Detection and Response) analysts noticed an inflow of malicious exercise focusing on on-premises SharePoint cases, together with malicious PowerShell instructions executed throughout a number of estates. Extra evaluation decided these occasions are doubtless the results of energetic, malicious deployment of an exploit generally known as ‘ToolShell.’
ToolShell collectively refers back to the chained exploitation of two SharePoint vulnerabilities, CVE-2025-49704 and CVE-2025-49706. The ToolShell exploit was unveiled on the Pwn2Own occasion in Berlin in Might 2025, and Microsoft launched patches for each vulnerabilities in its July Patch Tuesday launch.
Nonetheless, menace actors subsequently developed exploits that seem to bypass these patches, resulting in the publication of two new CVE-IDs: CVE-2025-53770 and CVE-2025-53771.
Sophos MDR has contacted all identified victims, however with these vulnerabilities beneath energetic exploitation we urge customers to use the relevant patches to on-premises SharePoint servers (in line with Microsoft, SharePoint On-line in Microsoft 365 is just not impacted) on the earliest alternative.
What we’ve seen
The malicious PowerShell instructions noticed by Sophos MDR drop a malicious aspx file on the following paths on an impacted SharePoint server:
C:PROGRA~1COMMON~1MICROS~1WEBSER~116TEMPLATELAYOUTSspinstall0.aspx C:progra~1common~1micros~1webser~116templatelayoutsinfo3.aspx
Whereas menace actors could select to deploy many alternative instruments, within the circumstances not too long ago noticed by Sophos, a webshell generally known as SharpViewStateShell was deployed and detected as Troj/WebShel-P.
In some circumstances, the menace actors have tried to entry machine keys by deploying a webshell through PowerShell, which triggers the Sophos safety Access_3b. Within the occasion the machine keys are compromised, it will likely be essential to rotate these keys utilizing the steering supplied by Microsoft.
What to do
Prospects working on-premises SharePoint cases are suggested to use the official patches from Microsoft and comply with the equipped suggestions for mitigation. Customers unable to patch for no matter cause ought to take into account taking cases offline briefly.
Moreover, we suggest that customers test for the existence of the recordsdata we talked about above, and if current, take away them. Customers must be suggested that there could also be further variations that Sophos has not but noticed; this checklist shouldn’t be handled as full.
What subsequent
Sophos MDR will proceed to actively monitor for indicators of post-exploitation exercise linked to this vulnerability. We’ll publish updates on this web page as additional related info turns into accessible.
