With WannaCry and now Petya we’re beginning to see how and why the new strain of ransomware worms are evolving and growing far more effective than previous versions.
I think there are 3 main factors: Propagation, Payload, and Payment.*
- Propagation: You ideally want to be able to spread using as many different types of techniques as you can.
- Payload: Once you’ve infected the system you want to have a payload that encrypts properly, doesn’t have any easy bypass to decryption, and clearly indicates to the victim what they should do next.
- Payment: You need to be able to take in money efficiently and then actually decrypt the systems of those who pay. This piece is crucial, otherwise people will quickly learn they can’t get their files back even if they do pay and be inclined to just start over.
WannaCry vs. Petya
WannaCry used SMB as its main spreading mechanism, and its payment infrastructure lacked the ability to scale. It also had a kill switch, which was famously triggered and halted further propagation.
Petya on the other hand appears to be much more effective at spreading since it’s using both EternalBlue and credential sharing
/ PSEXEC to infect more systems. This means it can harvest working credentials and spread even if the new targets aren’t vulnerable to an exploit.
[NOTE: This is early analysis so some details could turn out to be different as we learn more.]
What remains to be seen is how effective the payload and payment infrastructures are on this one. It’s one thing to encrypt files, but it’s something else entirely to decrypt them.
The other important unknown at this point is if Petya is standalone or a component of a more elaborate attack. Is what we’re seeing now intended to be a compelling distraction?
There’s been some reports indicating these exploits were utilized by a sophisticated threat actor against the same targets prior to WannaCry. So it’s possible that WannaCry was poorly designed on purpose. Either way, we’re advising clients to investigate if there is any evidence of a more strategic use of these tools in the weeks leading up to Petya hitting.
*Note: I’m sure there are many more thorough ways to analyze the efficacy of worms. These are just three that came to mind while reading about Petya and thinking about it compared to WannaCry.