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Dirtbags dressed up malware as legit app using Sony crypto-certs

Code-signing certificate revoked in wake of discovery

Miscreants were quick to capitalize on the theft of Sony's cryptographic certificates – used to sign a software nasty to make it look legit.

An analysis of malware dubbed Destover was published by Kaspersky Lab on Tuesday, and shows the code was signed using a private certificate belonging to Sony to evade malware filters.

These certificate were apparently taken from Sony Pictures servers, which were comprehensively ransacked by hackers at the end of November, and leaked online.

It's believed the infiltrators used a version of Destover to attack Sony's network. And it appears the stolen digital certs were used to sign another build of Destover on Friday, which then ended up in the wild over the weekend.

When Windows examines an executable, it looks to see if the program has been signed by a recognized, trusted developer before running the code. As far as the operating system was concerned, the signed Destover was legit.

"The stolen Sony certificates (which were also leaked by the attackers) can be used to sign other malicious samples," Kaspersky warned on Tuesday.

"In turn, these can be further used in other attacks. Because the Sony digital certificates are trusted by security solutions, this makes attacks more effective. We've seen attackers leverage trusted certificates in the past, as a means of bypassing whitelisting software and default-deny policies."

Sounds pretty scary, right? But before anyone panics, it's worth pointing out that malware writers can no longer use the code-signing keys.

The certificates were issued by DigiCert, a US biz that sells security certs. Kaspersky said it warned DigiCert about the issue, so El Reg checked with the crypto-company to find out what the situation was.

"This certificate is already revoked," a spokeswoman for DigiCert told The Register on Tuesday, meaning Windows systems should reject the Destover build when its cryptographic signature is checked by the operating system.

"We received a report about the malware last week and immediately revoked the certificate," she added.

If you've already downloaded and run the Sony-signed malware, well, bad luck: you're infected. If you haven't yet, your PC should kick it out as the cert is toast. So, no real need to panic – although you wouldn't guess that from Kaspersky's report today, cough. ®

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