A cybercriminal group that Microsoft tracks as Storm-1175 has been exploiting a severe vulnerability in the Fortra GoAnywhere software to deploy Medusa ransomware. The flaw, identified as CVE-2025-10035, is a critical deserialization bug that carries a perfect CVSS score of 10.0 and allows for command injection without needing any authentication. This security issue, which was patched in versions 7.8.4 and Sustain Release 7.6.3, lets attackers create a forged license response signature to execute arbitrary commands and potentially achieve remote code execution (RCE).
According to Microsoft Threat Intelligence, Storm-1175 is a cybercriminal group known for using Medusa ransomware and targeting public-facing applications for initial access. The exploitation of this vulnerability was first detected on September 11, 2025, affecting multiple organizations. However, research firm watchTowr revealed that active exploitation of the flaw had likely been happening since at least September 10, indicating the attackers had a head start before the vulnerability was publicly known.
After gaining initial access through the GoAnywhere vulnerability, the attackers follow a clear and damaging attack chain. They first drop remote monitoring and management (RMM) tools, such as SimpleHelp and MeshAgent, to maintain a persistent foothold on the network. They have also been observed creating malicious .jsp files within the GoAnywhere MFT directories at the same time the RMM tools are deployed.
In the subsequent phases of the attack, the threat actors execute commands to perform system and user discovery, map the network, and prepare for lateral movement. They commonly use mstsc.exe, the Windows Remote Desktop Connection tool, to move across the network. The installed RMM tools are then used for command-and-control (C2) communications, often routed through a Cloudflare tunnel. In at least one case, Microsoft observed the use of Rclone for data exfiltration before the final stage of the attack—the deployment of the Medusa ransomware.
The CEO and founder of watchTowr, Benjamin Harris, highlighted the lack of transparency from Fortra. He noted that organizations have been under silent assault for weeks with little information from the company. Harris emphasized that customers deserve answers, specifically about how the attackers obtained the private keys needed to exploit the flaw and why there was such a long period of silence before public disclosure. The lack of transparency has left many organizations in the dark about their exposure to this actively exploited vulnerability.
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