Microsoft Revokes Fraudulent Certificates Exploited by Rhysida Ransomware in 2025 Campaign
In June 2025, Microsoft discovered and responded to a sophisticated campaign in which a threat actor known as Vanilla Tempest (also tracked as Storm-0785) fraudulently issued over 200 code-signing certificates. These certificates were leveraged to make malicious files appear legitimate, facilitating the distribution of a fake Microsoft Teams installer that ultimately delivered the Oyster backdoor and deployed Rhysida ransomware across targeted environments. Microsoft quickly moved to revoke all compromised certificates to mitigate the risk and prevent further exploitation by the attackers. The breach highlights the growing sophistication of ransomware groups in leveraging trusted supply chain components for malware delivery. This incident underscores the heightened threat landscape in which adversaries exploit trusted relationships and digital certificates to evade security controls. It also signals an increasing trend of ransomware utilizing living-off-the-land and supply chain abuse techniques, compounding challenges for organizations striving to maintain software integrity and regulatory compliance.
Kill Chain