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Svante
Keymaster

Hi Cyril,

Thanks for the links.

The first paper, https://software.imdea.org/~juanca/papers/malsign_ccs15.pdf does not actually say anything about Authenticode signatures being weak or possible to manipulate. It says that computer system implementers (i.e. Microsoft), are not using it properly, not detecting situations that Authenticode indicates – in this case revoked certificates.

I should of course also point out that Authenticode as such, does not say  *anything* about the code, if it’s good, if it’s bad or if it’s ugly. It only strongly identifies the publisher, and make a strong statement that what you’re getting is what the publisher intended. If the publisher intends to publish malware, that can of course be signed. If this does happen, the idea with Authenticode is that you should then at least know who to sue or report to the police.

The second paper is interesting, and actually does to a certain extent demonstrate a weakness in the Authenticode implementation – they show they can *add* (not modify) arbitrary content while maintaining a valid signature. However, I’m actually at a loss to understand what they could *do* with this data, which the paper points out. Then it goes on to demonstrate an in-memory PE loader, which is also interesting – but to be honest, I don’t see how the one connects to the other. You still need to get that PE loader running. I guess you could write a software, include the PE loader, sign it – and then after that add the ‘payload’ as described but I don’t see the threat yet here. Then again – attacks never get worse, they only get better.

Thanks for two interesting reads! I don’t think it reduces trust in Authenticode as a signing mechanism from a known publisher (AxCrypt AB in this case) though.

We could certainly publish hashes of our executables, it doesn’t harm anything. I’m making a note of it, but since we don’t want any manual processes for stuff like that, we’ll need to add a few things to our platform so we can publish them automatically.

I still really, really want to get my hands on a sample of the file that seems to be signed January 5 and sort out what that is about. Probably its nothing, but we want to investigate.