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On Sunday, July 20, Microsoft Corp. issued an emergency security update for a vulnerability in SharePoint Server that is actively being exploited to compromise vulnerable organizations. The patch comes amid reports that malicious hackers have used the SharePoint flaw to breach U.S. federal and state agencies, universities, and energy companies.
Image: Shutterstock, by Ascannio.
In an advisory about the SharePoint security hole, a.k.a. CVE-2025-53770, Microsoft said it is aware of active attacks targeting on-premises SharePoint Server customers and exploiting vulnerabilities that were only partially addressed by the July 8, 2025 security update.
The Cybersecurity & Infrastructure Security Agency (CISA) concurred, saying CVE-2025-53770 is a variant on a flaw Microsoft patched earlier this month (CVE-2025-49706). Microsoft notes the weakness applies only to SharePoint Servers that organizations use in-house, and that SharePoint Online and Microsoft 365 are not affected.
The Washington Post reported on Sunday that the U.S. government and partners in Canada and Australia are investigating the hack of SharePoint servers, which provide a platform for sharing and managing documents. The Post reports at least two U.S. federal agencies have seen their servers breached via the SharePoint vulnerability.
According to CISA, attackers exploiting the newly-discovered flaw are retrofitting compromised servers with a backdoor dubbed “ToolShell” that provides unauthenticated, remote access to systems. CISA said ToolShell enables attackers to fully access SharePoint content — including file systems and internal configurations — and execute code over the network.
Researchers at Eye Security said they first spotted large-scale exploitation of the SharePoint flaw on July 18, 2025, and soon found dozens of separate servers compromised by the bug and infected with ToolShell. In a blog post, the researchers said the attacks sought to steal SharePoint server ASP.NET machine keys.
“These keys can be used to facilitate further attacks, even at a later date,” Eye Security warned. “It is critical that affected servers rotate SharePoint server ASP.NET machine keys and restart IIS on all SharePoint servers. Patching alone is not enough. We strongly advise defenders not to wait for a vendor fix before taking action. This threat is already operational and spreading rapidly.”
Microsoft’s advisory says the company has issued updates for SharePoint Server Subscription Edition and SharePoint Server 2019, but that it is still working on updates for supported versions of SharePoint 2019 and SharePoint 2016.
CISA advises vulnerable organizations to enable the anti-malware scan interface (AMSI) in SharePoint, to deploy Microsoft Defender AV on all SharePoint servers, and to disconnect affected products from the public-facing Internet until an official patch is available.
The security firm Rapid7 notes that Microsoft has described CVE-2025-53770 as related to a previous vulnerability — CVE-2025-49704, patched earlier this month — and that CVE-2025-49704 was part of an exploit chain demonstrated at the Pwn2Own hacking competition in May 2025. That exploit chain invoked a second SharePoint weakness — CVE-2025-49706 — which Microsoft unsuccessfully tried to fix in this month’s Patch Tuesday.
Microsoft also has issued a patch for a related SharePoint vulnerability — CVE-2025-53771; Microsoft says there are no signs of active attacks on CVE-2025-53771, and that the patch is to provide more robust protections than the update for CVE-2025-49706.
This is a rapidly developing story. Any updates will be noted with timestamps.
Microsoft today released updates to fix more than 60 security holes in Windows computers and supported software, including two “zero-day” vulnerabilities in Windows that are already being exploited in active attacks. There are also important security patches available for macOS and Adobe users, and for the Chrome Web browser, which just patched its own zero-day flaw.
First, the zero-days. CVE-2024-30051 is an “elevation of privilege” bug in a core Windows library. Satnam Narang at Tenable said this flaw is being used as part of post-compromise activity to elevate privileges as a local attacker.
“CVE-2024-30051 is used to gain initial access into a target environment and requires the use of social engineering tactics via email, social media or instant messaging to convince a target to open a specially crafted document file,” Narang said. “Once exploited, the attacker can bypass OLE mitigations in Microsoft 365 and Microsoft Office, which are security features designed to protect end users from malicious files.”
Kaspersky Lab, one of two companies credited with reporting exploitation of CVE-2024-30051 to Microsoft, has published a fascinating writeup on how they discovered the exploit in a file shared with Virustotal.com.
Kaspersky said it has since seen the exploit used together with QakBot and other malware. Emerging in 2007 as a banking trojan, QakBot (a.k.a. Qbot and Pinkslipbot) has morphed into an advanced malware strain now used by multiple cybercriminal groups to prepare newly compromised networks for ransomware infestations.
CVE-2024-30040 is a security feature bypass in MSHTML, a component that is deeply tied to the default Web browser on Windows systems. Microsoft’s advisory on this flaw is fairly sparse, but Kevin Breen from Immersive Labs said this vulnerability also affects Office 365 and Microsoft Office applications.
“Very little information is provided and the short description is painfully obtuse,” Breen said of Microsoft’s advisory on CVE-2024-30040.
The only vulnerability fixed this month that earned Microsoft’s most-dire “critical” rating is CVE-2024-30044, a flaw in Sharepoint that Microsoft said is likely to be exploited. Tenable’s Narang notes that exploitation of this bug requires an attacker to be authenticated to a vulnerable SharePoint Server with Site Owner permissions (or higher) first and to take additional steps in order to exploit this flaw, which makes this flaw less likely to be widely exploited as most attackers follow the path of least resistance.
Five days ago, Google released a security update for Chrome that fixes a zero-day in the popular browser. Chrome usually auto-downloads any available updates, but it still may require a complete restart of the browser to install them. If you use Chrome and see a “Relaunch to update” message in the upper right corner of the browser, it’s time to restart.
Apple has just shipped macOS Sonoma 14.5 update, which includes nearly two dozen security patches. To ensure your Mac is up-to-date, go to System Settings, General tab, then Software Update and follow any prompts.
Finally, Adobe has critical security patches available for a range of products, including Acrobat, Reader, Illustrator, Adobe Substance 3D Painter, Adobe Aero, Adobe Animate and Adobe Framemaker.
Regardless of whether you use a Mac or Windows system (or something else), it’s always a good idea to backup your data and or system before applying any security updates. For a closer look at the individual fixes released by Microsoft today, check out the complete list over at the SANS Internet Storm Center. Anyone in charge of maintaining Windows systems in an enterprise environment should keep an eye on askwoody.com, which usually has the scoop on any wonky Windows patches.
Update, May 15, 8:28 a.m.: Corrected misattribution of CVE-2024-30051.
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