Description

Cybercriminals are now exploiting Microsoft's Trusted Signing service to sign malware executables using short-lived three-day certificates, allowing malicious software to bypass security defenses. These signed executables appear legitimate because they are verified by Microsoft’s certification authority, making it harder for security systems to flag them as threats. While attackers previously sought Extended Validation (EV) certificates for their enhanced trust and SmartScreen reputation benefits, acquiring and maintaining them is both expensive and complex. As an alternative, cybercriminals are now leveraging Microsoft’s Trusted Signing service, which offers a simpler verification process while still providing sufficient trust for their operations. Although these certificates can be quickly revoked once identified, malware signed with them remains valid until that happens, enabling short-term attacks. Launched in 2024, Microsoft's Trusted Signing service was created to simplify code-signing for developers through a $9.99 monthly subscription. It enhances security by issuing short-lived certificates while preventing developers from directly accessing them, reducing the risk of theft. However, threat actors have found ways to abuse the system, using it to sign malware linked to campaigns such as Crazy Evil Traffers and Lumma Stealer. These certificates, issued by "Microsoft ID Verified CS EOC CA 01," are only valid for three days, but they still enable malware execution until explicitly revoked. Security researcher 'Squiblydoo' noted that attackers prefer this service over EV certificates due to its ease of use and the lack of strict validation requirements. In response, Microsoft has implemented threat intelligence monitoring to detect misuse and revoke compromised certificates. The company stated that certificates linked to malicious activity are promptly revoked, and the associated accounts are suspended. Despite these measures, the risk of abuse persists. To mitigate this, Microsoft now restricts certificate issuance under a company name to businesses with at least three years of operation. However, individual developers can still obtain certificates relatively easily, making it an attractive option for threat actors. Continuous monitoring and stricter policies are needed to curb the growing misuse of the service.?