Again and again: Signed Malware

"Certificates and CAs continue to be a hot topic (think Stuxnet, Duqu, Comodogate, Diginotar, et cetera).

Every now and then we run into malware that has been signed with a code signing certificate. This is problematic, as an unsigned Windows application will produce a warning to the end user if he downloads it from the web — signed applications won’t do this. Also some security systems might trust signed code more than unsigned code.

In some of these cases, the certificate has been created by the criminals just for the purpose for signing malware. In other cases they steal code signing certificates (and their passphrases) so they can sign code as someone else.

We recently found a sample signed with a stolen certificate. The file properties looked like this:

Publisher: Adobe Systems Incorporated
Copyright: Copyright (C) 2010
Product: Adobe Systems Apps
File version: 8, 0, 12, 78
Comments: Product of Adobe Systems

And the signing info was:

Digisign Server ID (Enrich)
GTE CyberTrust Global Root
Signing date: 5:36 24/08/2011

Turns out is part of the Government of Malaysia: Malaysian Agricultural Research and Development Institute. According the information we received from the Malaysian authorities, this certificate has been stolen “quite some time ago”.

The malware itself has been spread via malicious PDF files that drop it after exploiting Adobe Reader 8. The malware downloads additional malicious components from a server called Some of those components are also signed, although this time by an entity called

It’s not that common to find a signed copy of malware. It’s even rarer that it’s signed with an official key belonging to a government.

This particular malware does not gain much advantage of the signature any more, as the certificate expired in the end of September.

The Malaysian Government has been informed about the case."

Comodo Detected

Maybe digital signature should be cross referenced to the file details. If it says Adobe on one end and digital signature something else, warn user. But there is a problem where file doesn’t have any extra info but does have digital signature…