root labs rdist

August 14, 2012

Cyber-weapon authors catch up on blog reading

One of the more popular posts on this blog was the one pointing out how Stuxnet was unsophisticated. Its use of traditional malware methods and lack of protection for the payload indicated that the authors were either “Team B” or in a big hurry. The post was intended to counteract the breathless praise in the press for the advent of sophisticated “cyber-weapons”.

This year, more information was released in the New York Times that gave more support for both theories. The authors may not have had a lot of time due to political pressure and concern about Iran’s progress. The uneasy partnership between the US and Israel may have led to both parties keeping their best tricks in their back pockets.

A lot of people seemed skeptical about the software protection method I described called “secure triggers”. (I had written about this before also, calling it “hash-and-decrypt”.) The general idea is to gather information about the environment in order to generate a cryptographic key, which is used to decrypt the payload. If even one bit of info is incorrect, the payload can’t be decrypted. The analyst has to brute-force the proper environment, which can be made infeasible if there’s enough entropy and/or the validation method is too slow.

The critics claimed that secure triggers were too complicated or unable to withstand malware analyst scrutiny. However, this approach had been used successfully in everything from Core Impact to Blu-ray to Team Twiizers exploits, so it was feasible. Either the malware developers were not aware of this technique or there were other constraints, such as time, preventing it from being used.

Now we’ve got Gauss, which uses (surprise!) this exact technique. And, it turns out to be somewhat effective in preventing Kaspersky from analyzing the payload. We either predicted or caused the future, take your pick.

Is this the endgame? Not even, but it does mean we’re ready for the next stage.

The malware industry has had a stable environment for a while. Targeted attacks were rare, and most new malware authors hadn’t spent a lot of effort building in custom protection for their payloads. Honeypots and local analysis methods assume the code and behavior remain stable between the malware analyst’s environment and the intended target.

In the next stage, proper use of mechanisms like secure triggers will divide malware analysis into two phases: infection and payload. The infection stage can be analyzed with traditional techniques in order to find the security flaws exploited, propagation method, etc. The payload stage will change drastically, with more effort being spent on in situ analysis.

When the payload only decrypts and runs on a single target system, the malware analyst will need direct access to the compromised host. There are several forms this might take. The obvious one is providing a remote shell to the analyst to log in, attach a debugger, try to get a memory dump of the process, etc. This is dangerous because it involves giving an outsider access to a trusted system, and one that might be critical to other operations. Even if a whole-system memory dump is generated, say by physical access or a cold-boot attack, there is still going to be a lot of sensitive information there.

Another approach is emulation. The analyst uses a VM that turns all local syscalls into remote ones. This is connected to the compromised target host (or a clone of it), which runs a daemon to answer the API queries. The malware sample or relevant portions of it (such as the hash-and-decrypt routine) are run in the analyst’s VM, but the information the routine gathers comes directly from the compromised host. This allows the analyst to gather the relevant information while not having full access to the compromised machine.

In the next phase after this, malware authors add more anti-emulation checks to their payload decryption routine. They try to prevent this routine from being run in isolation, in an emulator. Eventually, you end up in a cat-and-mouse game of Core Wars on the live hardware. Malware keeps a closely-synchronized global heartbeat so that any attempt to dump and restart it on a single host corrupts its state irrecoverably. The payload, its triggers, and encryption keys evolve in coordination with the other hosts on the network and are tied closely to each machine’s identity.

Is this where we’re headed? I’m not sure, but I do know that software protection measures are becoming more, not less relevant.

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