Unknown threat actors have breached the National Nuclear Security Administration's network in attacks exploiting a recently patched Microsoft SharePoint zero-day vulnerability chain.

NNSA is a semi-autonomous U.S. government agency part of the Energy Department that maintains the country's nuclear weapons stockpile and is also tasked with responding to nuclear and radiological emergencies within the United States and abroad.

A Department of Energy spokesperson confirmed in a statement that hackers gained access to NNSA networks last week.

"On Friday, July 18th, the exploitation of a Microsoft SharePoint zero-day vulnerability began affecting the Department of Energy, including the NNSA," Department of Energy Press Secretary Ben Dietderich told BleepingComputer. "The Department was minimally impacted due to its widespread use of the Microsoft M365 cloud and very capable cybersecurity systems."

Dietderich added that only "a very small number of systems were impacted" and that "all impacted systems are being restored."

As first reported by Bloomberg, sources within the agency also noted that there's no evidence of sensitive or classified information compromised in the breach.

The APT29 Russian state-sponsored threat group, the hacking division of the Russian Foreign Intelligence Service (SVR), also breached the U.S. nuclear weapons agency in 2019 using a trojanized SolarWinds Orion update.
Attacks linked to Chinese state hackers, over 400 servers breached
On Tuesday, Microsoft and Google linked the widespread attacks targeting a Microsoft SharePoint zero-day vulnerability chain (known as ToolShell) to Chinese state-sponsored hacking groups.

"Microsoft has observed two named Chinese nation-state actors, Linen Typhoon and Violet Typhoon exploiting these vulnerabilities targeting internet-facing SharePoint servers," Microsoft said.

"In addition, we have observed another China-based threat actor, tracked as Storm-2603, exploiting these vulnerabilities. Investigations into other actors also using these exploits are still ongoing."

Dutch cybersecurity firm Eye Security first detected the zero-day attacks on Friday, stating that at least 54 organizations had already been compromised, including national government entities and multinational companies.

Cybersecurity firm Check Point later revealed that it had spotted signs of exploitation going back to July 7th targeting dozens of government, telecommunications, and technology organizations in North America and Western Europe.

krebsonsecurity.com - 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.
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.

forbes.com - Microsoft has confirmed that SharePoint Server is under mass attack and no patch is yet available — here’s what you need to know and how to mitigate the threat.

Microsoft Confirms CVE-2025-53770 SharePoint Server Attacks
It’s been quite the few weeks for security warnings, what with Amazon informing 220 million customers of Prime account attacks, and claims of a mass hack of Ring doorbells going viral. The first of those can be mitigated by basic security hygiene, and the latter appears to be a false alarm. The same cannot be said for CVE-2025-53770, a newly uncovered and confirmed attack against users of SharePoint Server which is currently undergoing mass exploitation on a global level, according to the Eye Research experts who discovered it. Microsoft, meanwhile, has admitted that not only is it “aware of active attacks” but, worryingly, “a patch is currently not available for this vulnerability.”

CVE-2025-53770, which is also being called ToolShell, is a critical vulnerability in on-premises SharePoint. The end result of which is the ability for attackers to gain access and control of said servers without authentication. If that sounds bad, it’s because it is. Very bad indeed.

“The risk is not theoretical,” the researchers warned, “attackers can execute code remotely, bypassing identity protections such as MFA or SSO.” Once they have, they can then “access all SharePoint content, system files, and configurations and move laterally across the Windows Domain.”

And then there’s the theft of cryptographic keys. That can enable an attacker to “impersonate users or services,” according to the report, “even after the server is patched.” So, even when a patch is eventually released, and I would expect an emergency update to arrive fairly quickly for this one, the problem isn’t solved. You will, it was explained, “need to rotate the secrets allowing all future tokens that can be created by the malicious actor to become invalid.”

And, of course, as SharePoint will often connect to other core services, including the likes of Outlook and Teams, oh and not forgetting OneDrive, the threat, if exploited, can and will lead to “data theft, password harvesting, and lateral movement across the network,” the researchers warned.