Cobalt Strike and Ransomware – Tracking An Effective Ransomware Campaign

Posted on August 31st, 2021

During the course of multiple incident response engagements, we encountered a persistent, unknown ransomware threat group utilizing an obfuscated Golang encryptor [1].  It is believed that the threat actors gained initial access through one or more SonicWall exploits [2], [3].  We can confirm prior sightings that Cobalt Strike was used by these threat actors to further gain access to exploit victim networks.  In this blog, we will highlight previously unreported infrastructure that is managed by this unknown threat group.

Indicators of Compromise

Victims are presented with the following ransom note:

Hello dear user!

Unfortunately, your files have been encrypted and attackers are taking over 300 GB of your personal data, financial reports and many other documents.

Do not try to recover files yourself, you can damage them without special software.

We can help you recover your files and prevent your data from leaking or being sold on the darknet.

Just contact support using the following methods and we will decrypt one non-important file for free to convince you of our honesty.

Contact us method below:

Use TOR Browser: http://[redacted].onion/[redacted]



A recent sample of the Golang packed malware was submitted to VirusTotal in mid July 2021 [4]:









The following domains have been attributed to the unknown threat group and have been observed hosting a Cobalt Strike server using TLS/SSL on non-standard ports.  It is clear that these threat groups are attempting to blend in with the noise by generating seemingly legitimate domains.


IP Addresses

The following IP addresses are related to the domains listed above and appear to be a single use.          


Am I impacted?

This threat group has been very active and if you or your organization utilized a SonicWall SMA VPN device since late 2020 or early 2021 without limited access, there is a likelihood that your organization has been compromised.  If you observe any connections to the domains listed above, it is very likely you are compromised.

What should I be doing to prevent these actors from disrupting our mission?

1. Back up (or start backing up!) all of your critical business data to an offline location.  We observed these threat actors identifying backup solutions employed by a victim and removing all backup files from an online 3rd party solution provider.

2. Patch and upgrade your SMA devices immediately.  More information can be found here:

3. Review all SMA logs looking for suspicious activity – specifically looking for successful authentication attempts from non-US based IP addresses and/or IP addresses that don’t originate from Internet service providers such as home or commercial ISPs.  

4. Enforce multi-factor authentication for all VPN accounts. 

5. Employ signatures to detect the above mentioned domains and hashes.

If you are in need of incident response support or ways to defend against this and other threats, please contact us at