Your Files Are Encrypted with a “Windows 10 Upgrade” – DON’T BE FOOLED!

Adversaries are always trying to take advantage of current events to lure users into executing their malicious payload. These campaigns are usually focused around social events and are seen on a constant basis. Today, Talos discovered a spam campaign that was taking advantage of a different type of current event.

Microsoft released Windows 10 earlier this week (July 29) and it will be available as a free upgrade to users who are currently using Windows 7 or Windows 8. This threat actor is impersonating Microsoft in an attempt to exploit their user base for monetary gain. The fact that users have to virtually wait in line to receive this update, makes them even more likely to fall victim to this campaign.

win10_blacked_out

Email Message

The email message above is a sample of the type of messages that users are being presented with. There are a couple of key indicators in the message worth calling out. First, the from address, the adversaries are spoofing the email to look like it is coming directly from Microsoft (update<at>microsoft.com). This is a simple step that tries to get users to read further.

win10_header

However, a quick look at the email header reveals that the message actually originated from IP address space allocated to Thailand.

Second, the attackers are using a similar color scheme to the one used by Microsoft.

Third, there are a couple of red flags associated with the text of the email. As you can see below, there are several characters that don’t parse properly. This could be due to the targeted audience, a demographic using a non-standard character set, or the character set the adversaries were using to craft the email.

Character_errors

Lastly, there are a couple other interesting techniques used by attackers to make the message appear authentic. One is the inclusion of a disclaimer message that looks similar to the one a user would receive from an email directly from Microsoft.

microsoft_callout

The other is a key piece of information added by adversaries that users are becoming more accustomed to seeing: an indication that the message attachment has been scanned by antivirus and appears to be a legitimate file.

malware_scan

This message links to a legitimate open source email filter and will trick some users into thinking the attachment is not malware.

Payload

Once a user moves past the email, downloads the zip file, extracts it, and runs the executable, they are greeted with a message similar to the following:

CTB-Locker

The payload is CTB-Locker, a ransomware variant. Currently, Talos is detecting the ransomware being delivered to users at a high rate. Whether it is via spam messages or exploit kits, adversaries are dropping a huge amount of different variants of ransomware. The functionality is standard however, using asymmetric encryption that allows the adversaries to encrypt the user’s files without having the decryption key reside on the infected system. Also, by utilizing Tor and Bitcoin they are able to remain anonymous and quickly profit from their malware campaigns with minimal risk.

TG-CTB-Locker

CTB-Locker has some interesting features that are different from large scale variants Talos has seen. First is the type of encryption used, most variants use RSA asymmetric encryption.  CTB-Locker actually makes use of elliptical curve encryption which still provides the same public/private key encryption but it’s a different type of algorithm, with lower overhead and the same level of security utilizing smaller key space. Second, there is the issue of the time window. CTB-Locker is only giving users 96 hours to pay for decryption, which is a shorter window than is standard for most ransomware.

The video below is courtesy of Cisco and it demonstrates how machine infections occur and the payload behind them:

Conclusion

The threat of ransomware will continue to grow until adversaries find a more effective method of monetizing the machines they compromise. As a defense, users are encouraged to backup their data in accordance with best practices. These backups should be stored offline to prevent them from being targeted by attackers.  Adversaries are always looking to leverage current events to get users to install their malicious payloads. This is another example, which highlights the fact that technology upgrades can also be used for malicious purposes. Talos is diligently working to detect and block these types of attacks as they occur and before users are potentially impacted.

Source found Here

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