China-Linked Storm-1175 Exploits Zero-Days to Rapidly Deploy Medusa Ransomware

A China-based threat actor known for deploying Medusa ransomware has been linked to the weaponization of a combination of zero-day and N-day vulnerabilities to orchestrate "high-velocity" attacks and break into susceptible internet-facing systems.

"The threat actor's high operational tempo and proficiency in identifying exposed perimeter assets have proven successful, with recent intrusions heavily impacting healthcare organizations, as well as those in the education, professional services, and finance sectors in Australia, the United Kingdom, and the United States," the Microsoft Threat Intelligence team said.

Attacks mounted by Storm-1175 have also leveraged zero-day exploits, in some cases, before they have been publicly disclosed, as well as recently disclosed vulnerabilities to obtain initial access. Select incidents have involved the threat actor chaining together multiple exploits (e.g., OWASSRF) for post-compromise activity.

Upon gaining a foothold, the financially motivated cybercriminal actor swiftly moves to exfiltrate data and deploy Medusa ransomware within a span of a few days, or, in select incidents, within 24 hours.

To aid in these efforts, the group creates persistence by creating new user accounts, deploying web shells or legitimate remote monitoring and management (RMM) software for lateral movement, conducting credential theft, and interfering with the normal functioning of security solutions, before dropping the ransomware.

Since 2023, Storm-1175 has been linked to the exploitation of more than 16 vulnerabilities -

CVE-2023-21529(Microsoft Exchange Server)CVE-2023-27351and CVE-2023-27350 (Papercut)CVE-2023-46805andCVE-2024-21887(Ivanti Connect Secure and Policy Secure)CVE-2024-1708andCVE-2024-1709(ConnectWise ScreenConnect)CVE-2024-27198andCVE-2024-27199(JetBrains TeamCity)CVE-2024-57726,CVE-2024-57727, andCVE-2024-57728(SimpleHelp)CVE‑2025‑31161(CrushFTP)CVE-2025-10035(Fortra GoAnywhere MFT)CVE-2025-52691andCVE-2026-23760(SmarterTools SmarterMail)CVE-2026-1731(BeyondTrust)

Both CVE-2025-10035 and CVE-2026-23760 are said to have been exploited as zero-days prior to them being publicly disclosed. As of late 2024, the hacking crew has exhibited a flair for targeting Linux systems, including exploiting vulnerable Oracle WebLogic instances across several organizations. However, the exact vulnerability that was being weaponized in these attacks remains unknown.

"Storm-1175 rotates exploits quickly during the time between disclosure and patch availability or adoption, taking advantage of the period where many organizations remain unprotected," Microsoft said.

Some of the notable tactics observed in these attacks are as follows -

• Using living-off-the-land binaries (LOLBins), including PowerShell and PsExec, along with Impacket for lateral movement.
• Relying on PDQ Deployer for both lateral movement and payload delivery, including Medusa ransomware, across the network.
• Modifying Windows Firewall policies to enable Remote Desktop Protocol (RDP) and deliver malicious payloads to other devices.
• Carrying out credential dumping using Impacket and Mimikatz.
• Configuring Microsoft Defender Antivirus exclusions to prevent it from blocking ransomware payloads.
• Leveraging Bandizip and Rclone for data collection and exfiltration, respectively.

The bigger implication here is that RMM tools like AnyDesk, Atera, MeshAgent, ConnectWise ScreenConnect, or SimpleHelp are becoming dual-use infrastructure for covert operations, as they allow threat actors to blend malicious traffic into trusted, encrypted platforms and reduce the likelihood of detection.