Threat Level: green Handler on Duty: Guy Bruneau

SANS ISC: CryptXXX ransomware updated - SANS Internet Storm Center SANS ISC InfoSec Forums

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CryptXXX ransomware updated


When generating exploit kit (EK) traffic earlier today, I noticed a change in post-infection activity on a Windows host infected with CryptXXX ransomware.  This happened after an infection caused by Neutrino EK triggered from the pseudoDarkleech campaign.

Shown above:  Flow chart for Neutrino EK/CryptXXX caused by pseudoDarkleech.

This morning, the decryption instructions for CryptXXX ransomware looked different.  A closer examination indicates CryptXXX has been updated.  As I write this, I haven't found anything online yet describing these recent changes, so this diary takes a quick look at the traffic.

Shown above:  An infected Windows desktop from earlier today.


Today's EK traffic was on using the same domain shadowing technique we've seen before from various campaigns using Neutrino EK (formerly using Angler EK [1, 2, 3] before Angler disappeared).  Post-infection traffic was over on TCP port 443 using custom encoding, a method CryptXXX has used since it first appeared earlier this year [4].

Shown above:  Traffic from today's Neutrino EK/CryptXXX infection filtered in Wireshark.

Below are some screenshots of the Neutrino EK traffic.

Shown above:  Neutrino EK landing page.

Shown above:  Neutrino EK sends a Flash exploit.

Shown above:  Neutrino EK sends the payload (it's encrypted).

In a change of behavior, text and HTML files for the CryptXXX decryption instructions are downloaded in the clear during the post-infection traffic.

Shown above:  Text-based decryption instructions sent on over TCP port 443.

Shown above:  HTML-based decryption instructions sent on over TCP port 443.

I used my Security Onion setup to see what Snort-based alerts triggered.  Looks like the EmergingThreats team already has a signature covering the new CryptXXX post-infection traffic.

Shown above:  My results from Sguil on Security Onion using the ET Pro ruleset.

Below are two screenshots with HTML decryption instructions from the infected Windows host's desktop.

Final words

Although I haven't noticed anything yet, I'm sure some of the usual sources will have a more in-depth article on these recent changes in CryptXXX ransomware.  This diary is just meant to give everyone a heads-up.

Pcap and malware for this diary are located here.

Brad Duncan
brad [at]




339 Posts
ISC Handler

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