Attackers Misused Code Signing Certificates of Taiwanese Companies to Spread Plead Malware

Security researchers identified a malware campaign in which attackers stole digital certificates from multiple Taiwanese technology firms and used them to spread the Plead backdoor.

According to WeLiveSecurity, researchers at Slovakian IT security company ESET first detected the operation when their systems received files marked as suspicious. Each of those files were digitally signed with a valid D-Link Corporation code-signing certificate. Additional analysis uncovered that D-Link had used that same certificate to sign some of its legitimate software, leading the researchers to believe that bad actors had stolen the certificate.

They also uncovered instances of the campaign leveraging a certificate presumably stolen from Changing Information Technology Inc, another technology company based in Taiwan.

All variants of the campaign used junk code to obfuscate their malware payload. But the malware behaved the same way in all versions. It accessed an encrypted binary blob by contacting a remote server or opening it from a local disk. This blob, in turn, contained encrypted shellcode which was responsible for downloading Plead malware.

Active since at least 2012, Plead is an information theft campaign that consists of two parts: the Plead backdoor and the Drigo exfiltration tool. The former is responsible for helping attackers to harvest credentials, open a remote shell and upload files, among other functions, on an infected machine. As explained by Trend Micro, the latter is useful in terms of searching infected computers for documents and uploading any files of interest to Google Drive accounts under the bad actors’ control.

For more information about Plead, please read this analysis published by JPCERT/CC.

ESET’s researchers reached out to D-Link Corporation about the compromised certificate. Upon learning of the campaign, the Taiwanese company launched its own investigation which culminated in its decision to revoke the misused certificate on 3 July. Changing Information Technology Inc. revoked their compromised certificate a day later, though ESET observed that those responsible for the attack campaign were still using the document to sign their malware as of 9 July.

This isn’t the first time ESET has spotted attackers misusing digital certificates. Anton Cherepanov, senior malware researcher at the firm, explained in the WeLiveSecurity alert that it’s a common evasive technique employed among digital attackers.

“Misusing digital certificates is one of the many ways cybercriminals try to mask their malicious intentions – as the stolen certificates let malware appear like legitimate applications, the malware has a greater chance of sneaking past security measures without raising suspicion.”

Given the utility of certificate misuse for malefactors, it’s important that organizations take steps to protect their digital certificates. One of the ways they can do so is by investing in an automated solution that helps them monitor their encryption keys and certificates for any abnormal behavior. Gain this level of complete visibility with Venafi today.

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