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'Spymel’ Is Latest Example Of Attackers Using Signed Malware

What was once reserved for targeted attacks is being increasingly used to distribute common crimeware payloads says Zscaler.

In another instance of the growing tendency by threat actors to use digital certificates in crimeware payloads, security vendor Zscaler Wednesday issued an alert on a new data stealing Trojan that uses a legitimately issued certificate to try and evade security tools.

The highly obfuscated spyware dubbed Spymel is digitally signed with a certificate that was originally issued by certificate authority DigiCert to an entity named SBO Invest.  DigiCert has since revoked the certificate but a newer version of Spymel has surfaced using another certificate issued to SBO Invest, Zscaler said.

In order to infect a Windows system, the attackers first send a malicious JavaScript file as an email attachment to victims. Spymel is downloaded and installed from a remote location on the systems of those who click open the attachment, the security vendor noted.

Once installed on a system, Spymel monitors Task Manager, Process Explorer and other applications. It logs keystrokes and is capable of preventing the victim from running software capable of terminating the malware. The malware communicates with a command and control server and sends information about all user activity and active processes running on the victim’s computer, Zscaler said.

What makes Spymel noteworthy is its use of a digital certificate to try and evade security software. Software vendors and websites use digital certificates to authenticate their products and to enable secure communications between a web browser and a server.

In recent years, malware authors have taken to stealing digital certs or to set up new certificate with fake information, which they then use to digitally sign their malware tools to make them appear legitimate.

“The digital certificate will give a false sense of authenticity to the end user especially when the certificate belongs to a legitimate software vendor,” says Deepen Desai, director of security research at Zscaler. “This approach also helps malware authors in evading detection as it is common for security vendors to bypass advanced heuristic checks for payloads that are signed using legitimate trusted certificates,” he said.

The use of such certificates is becoming increasingly common especially in creating botnets as well as spyware and adware payloads, he said.  Signed malware payloads have been around for years, he said but initially at least most of it was used for carrying out targeted attacks. It’s only relatively recently that threat actors have begun using digital certs to distribute other payloads as well, Desai said.

Most likely driving the trend is the improved infection rates that malware authors can achieve with signed malware and the higher possibility that signed malware has of evading malware detection tools he said.

“Additionally, it is very easy and inexpensive for the bad actors to setup a new certificate with fake information due to weaknesses in the vetting process of certain Certificate issuing authorities.”

This marks the second time in just the past few days that a security vendor has warned about threat actors using digital certs to distribute malware. Just last week, Proofpoint warned about rogue iOS application marketplaces springing up carrying malicious IOS applications signed with stolen enterprise certificates. According to Proofpoint, threat actors have figured out a way to “sideload” malicious applications even on non-jailbroken iOS devices by using digital signatures to fool iOS devices into installing the software.

 [For more on this topic, read 2015: The Year Of 'Attacks on Trust' by Kevin Bocek]

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