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Comodo Certificates Used to Sign Banking Trojans in Brazil

Researchers at Kaspersky Lab have discovered financial malware in Brazil that are signed with valid certificates from Comodo. To make matters worse, the certificates were using false registration details.

According to Kaspersky’s Fabio Assolini, the researcher who discovered the signed banking Trojan, it’s relatively simple for a criminal to purchase a code signing certificate and use it for malware. It’s nothing new; criminals have used stolen certificates and valid certificates in the past. It sometimes helps to sign software, as it offers a since of legitimacy and it can help with propagation.

“Now Brazilian cybercriminals have started using this technique in their malware in an attempt to gain more time to spread files undetected. Recently we found a Trojan banker signed with a valid digital certificate issued by a CA. It appears that fake company data was used to obtain the certificate,” Assolini wrote.

According to Comodo, they do “a considerable amount of background checking” after the Code Signing Certificate application is submitted. “As a result, it will take approximately 3-5 days to verify your information and issue a Digital ID,” the CA explains.

If that is so, then there is a problem in the process. The Comodo issued cert used by the banking malware was registered using fake business information and a Yahoo email address. So at a cost of $180 per year, combined with an easily bypassed verification process, criminals know they will make their money back on the certificate purchase after a single victim.

The maliciously used certs were revoked after 15 days by Comodo. However, by the time they were aware of the problem (a local security company notified them), the malware had already infected banking customers in Brazil by posing as an emailed banking update.

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Steve Ragan is a security reporter and contributor for SecurityWeek. Prior to joining the journalism world in 2005, he spent 15 years as a freelance IT contractor focused on endpoint security and security training.