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A crucial safety vulnerability in Microsoft SharePoint Server has been weaponized as a part of an “energetic, large-scale” exploitation marketing campaign.
The zero-day flaw, tracked as CVE-2025-53770 (CVSS rating: 9.8), has been described as a variant of CVE-2025-49706 (CVSS rating: 6.3), a spoofing bug in Microsoft SharePoint Server that was addressed by the tech big as a part of its July 2025 Patch Tuesday updates.
“Deserialization of untrusted information in on-premises Microsoft SharePoint Server permits an unauthorized attacker to execute code over a community,” Microsoft stated in an advisory launched on July 19, 2025.
The Windows maker additional famous that it is getting ready and absolutely testing a complete replace to resolve the problem. It credited Viettel Cyber Security for locating and reporting the flaw by means of Trend Micro’s Zero Day Initiative (ZDI).
In a separate alert issued Saturday, Redmond stated it is conscious of energetic assaults concentrating on on-premises SharePoint Server clients, however emphasised that SharePoint Online in Microsoft 365 will not be impacted.
In the absence of an official patch, Microsoft is urging clients to configure Antimalware Scan Interface (AMSI) integration in SharePoint and deploy Defender AV on all SharePoint servers.
It’s price noting that AMSI integration is enabled by default within the September 2023 safety replace for SharePoint Server 2016/2019 and the Version 23H2 function replace for SharePoint Server Subscription Edition.
For those that can not allow AMSI, it is suggested that the SharePoint Server is disconnected from the web till a safety replace is accessible. For added safety, customers are really useful to deploy Defender for Endpoint to detect and block post-exploit exercise.
The disclosure comes as Eye Security and Palo Alto Networks Unit 42 warned of assaults chaining CVE-2025-49706 and CVE-2025-49704 (CVSS rating: 8.8), a code injection flaw in SharePoint, to facilitate arbitrary command execution on inclined situations. The exploit chain has been codenamed ToolShell.
But provided that CVE-2025-53770 is a “variant” of CVE-2025-49706, it is suspected that these assaults are associated.
The malicious exercise basically includes delivering ASPX payloads by way of PowerShell, which is then used to steal the SharePoint server’s MachineKey configuration, together with the ValidationKey and DecryptionKey, to take care of persistent entry.
The Dutch cybersecurity firm stated these keys are essential for producing legitimate __VIEWSTATE payloads, and that having access to them successfully turns any authenticated SharePoint request right into a distant code execution alternative.
“We are nonetheless figuring out mass exploit waves,” Eye Security CTO Piet Kerkhofs instructed The Hacker News in a press release. “This can have a huge effect as adversaries are laterally transferring utilizing this distant code execution with pace.”
“We notified nearly 75 organisations that acquired breached, as we recognized the malicious net shell on their SharePoint servers. In this group are large corporations and huge authorities our bodies internationally.”
It’s price noting that Microsoft has but to replace its advisories for CVE-2025-49706 and CVE-2025-49704 to mirror energetic exploitation. We have additionally reached out to the corporate for additional clarification, and we are going to replace the story if we hear again.
(The story is creating. Please examine again for extra particulars.)