Exposing Fox Tempest: A malware-signing service operation

Fox Tempest is a financially motivated threat actor operating a malware‑signing‑as‑a‑service (MSaaS) used by other cybercriminals, including Vanilla Tempest and Storm groups, to more effectively distribute malicious code, including ransomware. The post Exposing Fox Tempest: A malware-signing service operation appeared first on Microsoft Security Blog .

In this article Fox Tempest’s role and impact Fox Tempest’s malware signing as a service infrastructure Defending against Fox Tempest-enabled attacks Microsoft Defender detections Indicators of compromise Fox Tempest is a financially motivated threat actor that operates a malware-signing-as-a-service (MSaaS)  used by other cybercriminals to more effectively distribute malicious code, including ransomware. The threat actor abuses Microsoft Artifact Signing to generate short-lived, fraudulent code-signing certificates to appear legitimately signed, allowing malware to evade security controls.

Fox Tempest has created over a thousand certificates and established hundreds of Azure tenants and subscriptions to support its operations. Microsoft has revoked over one thousand code signing certificates attributed to Fox Tempest. In May 2026, Microsoft’s Digital Crimes Unit (DCU), with support from industry partner  Resecurity , disrupted Fox Tempest’s MSaaS offering , targeting the infrastructure and access model that enables its broader criminal use.

From service to shutdown How Microsoft disrupted Fox Tempest ↗ Microsoft Threat Intelligence observed Fox Tempest’s operations enabling the deployment of Rhysida ransomware by threat actors such as Vanilla Tempest , as well as the distribution of other malware families including Oyster, Lumma Stealer , and Vidar. The consistency, scale, and downstream impact of the resulting attack activity demonstrate that Fox Tempest is a vital operator within the broader cybercrime ecosystem.

know the threat Identify and defend against ransomware attacks › In this blog, we examine how Fox Tempest’s MSaaS operation functioned and how it enabled the delivery of trusted, signed malware across the cybercrime ecosystem. We also provide Microsoft Defender detections, indicators of compromise (IOCs), and mitigation recommendations to help organizations identify and disrupt similar activity. Fox Tempest’s role and impact Fox Tempest doesn’t directly target victims but instead provides supporting services that enable ransomware operations by other threat actors. Microsoft Threat Intelligence has tracked Fox Tempest since September 2025.

Microsoft Threat Intelligence has linked the actor to various ransomware groups including Vanilla Tempest, Storm-0501 , Storm-2561 , and Storm-0249, who have all leveraged Fox Tempest-signed malware in active intrusions. Malware delivery in these attacks have included use of legitimate purchased advertisements, malvertising, and SEO poisoning.

Storm-2561 SEO poisoning Fake VPN clients steal credentials › Cryptocurrency analysis associated with Fox Tempest has identified clear links tying the actor to ransomware affiliates responsible for delivering several prominent ransomware families, including INC, Qilin, Akira, and others, with observed proceeds in the millions.