Atrás 
Summary
CrossLock is a ransomware group that emerged in April 2023, targeting a large digital certifier company in Brazil. This ransomware was written in Go, which has also been adopted by other ransomware groups, including Hive, due to the cross-platform capabilities offered by the language. CrossLock operates in the double-extortion scheme, by threatening to leak stolen data on a website hosted on the deep web if the ransom isn’t paid by the victim.
In this blog post, we will show how the CrossLock ransomware works.
Analysis
The CrossLock ransomware was developed in the Go programming language, and was likely compiled on April 16, 2023, which is the same day where the attackers added the Brazilian digital certifier in their deep web site.
Attackers can use CrossLock to infect not only a local system, but also a remote system by using their custom parameters, which are described below:
| Parameter | Description |
|---|---|
| --path, -P | Encrypt the specified path |
| --host, -H | Remote system to run CrossLock (which can be a DNS or an IP address) |
| --domain, -d | The domain name (default is “.”) |
| --user, -u | Username used to authenticate in the remote system |
| --pwd, -p | Password of the user specified in “-u” or “--user” |
| --uac, -ub | If specified, tries to bypass Windows UAC to run with elevated privileges |
Like other ransomware families, such as BlackCat, CrossLock offers a “help” menu to provide instructions on how to use these parameters. They even included an example on how to execute CrossLock on a remote system and encrypt the entire file directory.
When executed, CrossLock outputs what it’s doing to a console. Also, the attacker left a few debug logs enabled, so it’s possible to get more insights of what it’s doing by just looking at the output.
To avoid detection, CrossLock bypasses the Event Tracing for Windows (ETW), which is a mechanism that provides system and application logs that can be used by developers for debugging. This is done through a common API hooking technique, by patching functions EtwEventRegister, EtwNotificationRegister, EtwEventWriteFull, and EtwEventWrite on “ntdll.dll”.
CrossLock has a hardcoded list of services and processes that it tries to stop before encrypting files, which is a common practice among ransomware families. First, it tries to stop services related to backup services, databases, and security software. Then, it tries to stop a series of processes. The complete list of services and processes it tries to stop can be found in our GitHub repository.