The hackers that compromised Sony Pictures Entertainment's network leaked extremely sensitive information-technology credentials, including a collection of passwords and hundreds of certificates, one of which was used to sign the same malware used by the attackers to compromise the company.
On Dec. 9, security firm Kaspersky Lab revealed that its products detected "an unusual sample" of the Destover malware, used by attackers against Korean targets in the DarkSeoul operation and against Sony Pictures in the most recent breach. A copy of the malware dating back to July had been signed on Dec. 5 using a code-signing certificate compromised during the Sony breach, the company said.
The malware is not being used in attacks. In fact, the day after Kaspersky Lab's announcement, a security researcher claimed that "a researcher who doesn't want to be named" had used the certificate—found in the leaked Sony files—to sign a copy of the Destover malware as a joke.
Kaspersky Lab's analyst could not confirm the claims, but said that the leak of the certificate should be considered a problem for security professionals.
"The existence of this sample demonstrated that the private key was in the public domain," Kaspersky Lab's Global Research and Analysis Team, told eWEEK in an email interview. "At that point, we knew we had an extremely serious situation at hand, regardless of who was responsible for signing this malware."
Sony has lost a great deal of sensitive data in the massive breach, which likely had gone on for months but which the company only discovered in late November after the attackers announced their presence by deleting files and defacing systems with digital wallpaper. Hundreds of digital certificates, used to designate trusted content on the Internet, and a folder full of passwords were among the data leaked to the Internet.
The passwords could be used to access a variety of business accounts used by Sony Pictures and its employees, while the code-signing certificates could be used to camouflage future attacks, making antivirus software more likely to trust signed code.
"The importance of leaked code-signing keys cannot be overestimated," the Global Research and Analysis Team said. "Software signed by a trusted publishing house will generally be trusted by the operating system, security software and first responders. It's an extremely powerful way for attackers to stay below the radar."
The certificate used to sign the Destover malware sample had been protected by a password, but the password was the name of the file, according to media reports.
Kaspersky Lab and other security experts have criticized Sony Pictures for not immediately revoking the stolen certificates. "Certificate revocation needs to be a top priority when responding to a major malware and breach incidents," the company said.
Kaspersky Lab also took aim at the anonymous researcher signing old malware using the stolen certificate, saying that the stunt was unnecessary.
"The certificate would have been revoked without the creation of new malware," the Global Research and Analysis Team said. "There really was no need to create new malware to prove that the certificate hadn't been revoked yet."