Microsoft SharePoint attacks ensnare 400 victims, including federal agencies

The fallout from an attack spree targeting defects in on-premises Microsoft SharePoint servers continues to spread nearly a week after zero-day exploits were discovered, setting off alarms across the globe. More than 400 organizations have been actively compromised across four waves of attacks, according to Eye Security.

Multiple government agencies, including the Departments of Energy, Homeland Security and Health and Human Services, have been hit. The California Independent System Operator, which operates some of the state’s wholesale electric grid, was also impacted.

As more victims confirm varying levels of compromise from the attack spree, researchers are learning and sharing more details about post-exploit activities. One of the China-based attackers behind the initial wave of attacks, Storm-2603, deployed Warlock ransomware starting July 18, Microsoft Threat Intelligence said Wednesday in an updated blog post.

The Chinese government-affiliated threat groups Linen Typhoon and Violet Typhoon — which have been active for at least a decade — are also actively exploiting the zero-day vulnerabilities, Microsoft said. Linen Typhoon has focused on stealing intellectual property and Violet Typhoon is an espionage threat group. Storm is a moniker Microsoft uses for threat groups in development.

Microsoft said it observed Storm-2603 modifying policy settings to distribute Warlock ransomware in compromised environments. The attacker is also attempting to steal cryptographic keys from compromised SharePoint servers, which could allow attackers to maintain persistent access to victim environments after the patch has been applied. Microsoft did not say how many organizations have been hit with ransomware.

The zero-days under active exploit —  CVE-2025-53770 and CVE-2025-53771 — are variants of a pair of previously disclosed vulnerabilities — CVE-2025-49706 and CVE-2025-49704 — Microsoft addressed in its security update earlier this month. After discovering the new flaws, Microsoft scrambled to develop patches, releasing the updates for all affected versions of SharePoint by late Monday.

The exploit dubbed “ToolShell,” which allows attackers to bypass multi-factor authentication and single sign-on, contains the newly discovered defects: CVE-2025-53770, a critical remote-code execution vulnerability, and CVE-2025-53771, a security-bypass vulnerability. 

The “ToolShell” exploit chain allows attackers to fully access SharePoint content and execute code over the network, the Cybersecurity and Infrastructure Security Agency said. ESET Labs researchers said threat groups often chain all four vulnerabilities to intrude organizations.

CISA added CVE-2025-53770 to its known exploited vulnerabilities catalog Sunday, and added CVE-2025-47904 and CVE-2025-47906 to the database Tuesday. CISA said CVE-2025-53770 is a patch bypass for CVE-2025-49704 and CVE-2025-53771 is a patch bypass for CVE-2025-49706.

Officials declined to describe the level of compromise sustained across the federal government.

“Once the Microsoft SharePoint vulnerability was identified on Friday, CISA quickly launched a national coordinated response through an initial alert and two cybersecurity updates,” a Department of Homeland Security spokesperson said in a statement. “CISA has been working around the clock with Microsoft, impacted agencies, and critical infrastructure partners to share actionable information, apply mitigation efforts, implement protective measures, and assess preventative measures to shield from future attacks.”

The spokesperson said an investigation to identify potential exposure remains ongoing, adding “there is no evidence of data exfiltration at DHS or any of its components at this time.”

The Energy Department, which was impacted along with the National Nuclear Security Administration, is also unaware of any compromise of sensitive or classified information. 

Exploitation of the Microsoft SharePoint zero-day vulnerability began affecting the Energy Department and the NNSA on Friday. “The department was minimally impacted due to its widespread use of the Microsoft 365 cloud and very capable cybersecurity systems,” an agency spokesperson said in a statement.

“A very small number of systems were impacted. NNSA is taking the appropriate action to mitigate risk and transition to other offerings as appropriate,” the spokesperson added.

The Department of Health and Human Services said it is monitoring, identifying and mitigating all risks to its IT systems posed by the Microsoft SharePoint vulnerability. “This vulnerability is not unique to HHS and has been observed in other federal agencies and the private sector,” a spokesperson for the agency said in a statement. “At present, we have no indication that any information was breached as a result of this vulnerability.”

Jayme Ackemann, director of communications at the California Independent System Operator, said the nonprofit, which manages long-distance power lines across 80% of California’s grid, became aware of potential exploitation Sunday. “There has been no impact to market operations or grid reliability due to this incident,” Ackemann said. “All systems remain stable and fully operational.”

Microsoft SharePoint is prevalent across enterprise and government and deeply integrated with Microsoft’s platform. Researchers warn that attackers could use intrusions to burrow deeper into victim networks.

Attacks have spread globally but U.S.-based organizations are the most heavily targeted to date, accounting for more than 13% of attacks, according to ESET’s telemetry data. Scans from the Shadowserver Foundation showed nearly 11,000 SharePoint instances were still exposed to the internet as of Wednesday.