The ransomware was first noticed on Fridayand spread very quickly through many large organizations worldwide [verge]. Unlike prior ransomware, this sample used the SMBv1 ETERNALBLUE exploit to spread. ETERNALBLUE became public about a month ago when it was published as part of the Shadowbroker archive of NSA hacking tools [shadow].
A month prior to the release of the hacking tool, Microsoft had patched the vulnerability as part of the March Patch Tuesday release. The patch was released for Windows Vista, Windows Server 2008 and later versions of Windows as part of MS17-010 in March [MS17-010]. In response to the rapid spread of WannaCry, on Friday Microsoft released a patch for older versions of Windows, going back to Windows XP and Windows Server 2003 [msft].
At the time of the initial WannaCry outbreak, we also noticed a significant increase in scanning for port 445 [port445]. The increase was likely caused by infected systems scanning for more victims. It is not clear how the infection started. There are some reports of e-mails that include the malware as attachment seeding infected networks. But at this point, no actual samples have been made public. It is possible that the worm entered acorporate network via vulnerable hosts that had port 445 exposed to the internet. The WannaCry malware itself does have no e-mail component.
The malware will first check if it can reach a specific website at http://www.iuqerfsodp9ifjaposdfjhgosurijfaewrwergwea.com.
It will also check if a registry key is present. It will not run if either the registry key is present or the website is reachable. The domain has been registered and a web server has been set up by a security researcher. This significantly reduced the impact of WannaCry. A tool was released that will assist in setting the registry keys, which will also reduce the risk of infection. Over the weekends, reports indicated that new versions of the worm were spreading that used slightly different kill switches. But all current versions check a website and check for registry keys.
The malware creates a 2048 bit RSA key pair. The private key is encrypted using a public key that is included with the malware. For each file, a new random AES key is generated. This random AES key is then encrypted using the public user key. To decrypt the files, the users private key needs to be decrypted, which requires the malware authors private key. Unlike some other ransomware, no network communication is needed to generate these keys [pastebin]. The password [email protected] is not used to encrypt files. It is only used by the malware to decrypt some of its components. [endgame]
Encrypted files use the extension. wncry. To decrypt the files, the user is asked to pay $300, which will increase to $600 after a few days. The ransomware threatens to delete all files after a week.
In addition to encrypting files, the malware also installs 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 been reported over the weekend with slight changes to the kill switch domain and registry keys.
We expect to reduce the Infocon back to green on Monday.
What Can You do to prevent Infection?
- Apply MS17010 to Windows Vista and later (Windows Server 2008 and later)
- Apply Fridays patch to Windows XP or Window Server 2003.
- Verify correct patch application
- Make sure the kill switch domain is reachable from your network without proxy. If not, setup an internal DNS sinkhole
- Deploy the registry key inoculation [terstopper]
- Disable SMBv1
- Make sure systems are running up to date anti-malware
Indicators of Compromise:
PowerPoint for Presentations to Management
Friday SANS Webcast with technical details
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Article Link: https://isc.sans.edu/diary.html?storyid=22420&rss