Want to get around app whitelists by pretending to be Microsoft? Of course you can...

...And here's how

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DerbyCon A sprinkle of code and an understanding of the Windows digital certificate process is all that's needed for a miscreant to sneak malware past Microsoft's application whitelist within a corporate environment.

In a keynote address at the DerbyCon hacking conference in Kentucky, USA, on Friday, Matt Graeber, a security researcher with SpecterOps, detailed how he managed to disguise and run a banned software nasty as a legit whitelisted app, and thus bypass Redmond's security mechanisms.

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Usually anyone trying to fool Microsoft's defenses in this way, via PowerShell, will be caught by the executable signature checks within the Get-AuthenticatedSignature function. However, according to Graeber, there’s also CryptSIPVerifyIndirectData, which can be abused to green-light malicious applications with a counterfeit signature. The only thing you need are some coding tools and, oh yeah, admin privileges on the target computer, we're told.

“By fooling PowerShell signature checking I could validate myself as anyone,” Graeber said. “I am Microsoft at this point. I can be Google, I can be anyone I want to be. I can do this remotely and it's not hard to get admin privileges.”

Graeber said that he has since verified that malware using bogus signatures to masquerade as white-listed programs can be validated and run within non-PowerShell environments on Windows. He has detailed the whitelist bypass technique in this here white paper [PDF] if you want all the techie details. ®

PS: There are other ways, of course, to run rogue programs you're not supposed to on Windows.


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