Microsoft Revokes 200+ Fraudulent Code-Signing Certificates
🔒 Microsoft disclosed it revoked more than 200 certificates after a threat actor tracked as Vanilla Tempest used them to fraudulently sign malicious binaries, including fake Microsoft Teams installers that delivered the Oyster backdoor and led to Rhysida ransomware deployments. The activity was detected in late September 2025 and disrupted earlier this month, and Microsoft has updated security solutions to flag the associated signatures. The actor abused SEO poisoning and bogus download domains impersonating Teams to distribute trojanized installers. Users are advised to download software only from verified sources and to avoid suspicious links or ads.
