The WannaCry ransomware was first noticed on May 12, 2017 and it spread very quickly through many large organizations, infecting systems worldwide. Unlike other ransomware, this sample used the SMBv1 “ETERNALBLUE” exploit to spread. “ETERNALBLUE” became public about a month prior when it was published as part of the Shadowbroker archive of NSA hacking tools.
Prior to the release of the hacking tool, Microsoft had patched the vulnerability as part of the March 2017 Patch Tuesday release. The patch was released for only supported versions of Windows. In response to the rapid spread of WannaCry, Microsoft eventually released a patch for later versions of Windows as part of MS17-010, going back to include the still popular Windows XP and Windows Server 2003.
One way to detect the spread of the malware was the significant increase in activity on port 445. The increase was caused by infected systems scanning for more victims. It is still not clear how the infection started. There are some reports of e-mails that included the malware as an attachment, but at this point no actual samples have been made public. It is also possible that the worm entered a corporate network via vulnerable hosts that had port 445 exposed to the internet. The WannaCry malware itself doesn’t have an e-mail component.
At startup, the malware was first checking if it can reach a specific website at http://www.iuqerfsodp9ifjaposdfjhgosurijfaewrwergwea.com, but it can no longer be assumed that newer versions will still demonstrate this behavior. This was a simple “kill-switch”, since if it found the site it would stop operations.
Eventually, the malware would create an encryption key and encrypt all the user files on the infected PC to prevent normal user access to those files. The idea is to force the user to pay a fee to recover the files they no longer could access.
Encrypted files use the extension: wncry. To decrypt the files, the user is asked to pay $300, which increased to $600 after a few days. The ransomware threatened to delete all user files after a week waiting period.
In addition to encrypting files, the malware also installed a “DOUBLEPULSAR” back door. The backdoor could be used to compromise the system further. The malware will also install Tor to facilitate communication with the ransomware author.
New variants have already been reported with slight changes to the kill switch domain and other settings. There is also a decryption key that can be used on many systems, but prevention is always better than sarching for recovery options.
If your version of Windows was supported and you installed all available patches from Microsoft, your system would not have been infected. Microsoft also announced that the new “Windows 10 S” would help prevent ransomware infection as it will only run software purchased from the Microsoft Store.