Can someone provide a simple (but not overly so) explanation of how the current generation of ransomware operate i.e., A) spread and B) lock up the computer? Does it always require human intervention for A. ? Thank you.
Where attacker == the ransomware executable:
First is the EternalBlue exploit developed by and leaked from the NSA. EternalBlue exploits a flaw in Windows systems on port 445 TCP that can be used to take complete control of an unpatched system. So if an attacker can connect to a vulnerable Windows machine on port 445 tcp they can take control of that machine.
There are also indications that this ransomware sample spreads using legitimate administrative tools in Windows systems such as WMI (execute commands on a remote system if you an administrator account on that PC), and PSEXEC (mount shares on the remote system if you have an administrator account, execute command if ''). These are legitimate (but legacy) Windows components that normally facilitate the management of client PC's when they're connected to a domain at a company or school. So if an attacker can connect to a Windows machine on port 445 tcp (PSEXEC) or 135 (WMI) AND have administrative credentials for that PC they can take complete control of that machine.
These two are probably part of how the ransomware spreads once it gets inside your network. The wcry outbreak a few weeks ago gained access to networks by infecting one or several people via a phishing e-mail with malicious files/links-to-files inside. AFAIK it's currently still unknown/unconfirmed how this outbreak spreads precisely but I'd guess it's either actively being spread by phishing OR it's been present but dormant in these networks for a while after having been installed by phishing over a longer period of time.
If an attacker possesses a 0-day then all bets are probably off, and even step A would not necessarily require any human interaction.
This outbreak is particularly nasty because after it's done encrypting files it supposedly triggers a crash that forces the system to restart. (handy for servers where a user is not normally able to restart the system). Because the system restarts any, artefacts from the encryption process that might be used to decrypt files without paying or restoring backups are gone.
Source:https://www.us-cert.gov/ncas/alerts/TA17-132A
"Once the malware starts as a service named mssecsvc2.0, the dropper attempts to create and scan a list of IP ranges on the local network and attempts to connect using UDP ports 137, 138 and TCP ports 139, 445. If a connection to port 445 is successful, it creates an additional thread to propagate by exploiting the SMBv1 vulnerability documented by Microsoft Security bulliten MS17-010."
B) Once a piece of ransomware is running on your computer, it can generate an encryption key and send that back to its controller machine, then start encrypting files on the computer.
"A" shouldn't be able to happen on its own on a properly firewalled network, I think. So the start of the spread might be someone clicking an e-mail link that they shouldn't, and the infection works to spread on its own once inside a network.
b) They encrypt your files and make you pay usually with a time limit before they just delete the files
Usually if it says "0-Day" assume that it can be exploited without human intervention a-la stuxnet
That's not at all what a 0-day means, it just means a previously unknown vulnerability. We've never seen a ransomware attack anywhere close to as sophisticated at Stuxnet. This latest attack is nothing new and is only affecting people who haven't kept their systems up to date.
Please don't assume I don't know what 0-day actually means. I chose my words carefully as not not imply that I was saying the definition of the term.
Typically when we see news using the term 0-day it's because there was no human element needed in the infection of machines. Thinking back in recent memory (17~ years) I can't remember a time when 0-day was used when it didn't mean autonomous infection.
Although. I fully understand that the term means that it's a previously unknown issue. Which is why I chose my words as carefully as I did.
The reason human intervention is generally required now is because Windows has been hardened enough that some idiot user has to click a button to bypass the built-in basic protection. There's still a possibility of a "0-day" exploit remote-owning a machine, though these sorts of exploits are a lot harder to craft due to that attack surface being exposed to more security scrutiny.