Ransomware Gangs Increasingly Use Skitnet Post-Exploitation Malware
Summary:
Skitnet is a highly modular and multi-stage malware strain attributed to the threat actor LARVA-306. It combines multiple programming languages, including Rust, Nim, PowerShell, and .NET, to maintain stealthy and persistent access to targeted systems. The initial stage, a Rust binary, decrypts and manually maps an embedded Nim payload using ChaCha20 encryption and the DInvoke-rs library for reflective code loading. This Nim binary establishes a DNS-based reverse shell by dynamically resolving APIs and crafting DNS queries to the C2 server. It then launches a cmd[.]exe process, with multiple threads handling DNS polling and encrypted communication. Skitnet’s command-and-control panel manages infected devices using C drive serial numbers as unique identifiers and enforces filters for geographic and network-based targeting. It also employs a Bash-based automated setup and cleans up forensic artifacts like SSH logs, command history, and IP traces, enhancing its operational stealth.
Once persistence is achieved, primarily through DLL hijacking of a signed Asus binary (ISP.exe) and PowerShell scripts, Skitnet enables several post-compromise capabilities via its control panel. Supported commands include ‘startup’ for persistence, ‘screen’ for screenshot capture (uploaded to Imgur), and ‘anydesk/rutserv’ for the silent deployment of legitimate remote access tools. Also supported is the ‘shell’ command, which enables real-time remote command execution via PowerShell and persistent polling for new tasks, as well as an ‘av’ command that is designed to collect installed security software information using WMI queries. A .NET-based loader extends Skitnet’s modularity, decoding and executing additional obfuscated payloads using RC4 decryption, where keys and parameters are embedded in environment variables. These secondary payloads connect to dynamically constructed C2 URLs for further instructions or malware downloads.
Security Officer Comments:
Skitnet has been actively marketed on underground forums such as RAMP since April 2024 and is believed to be developed and distributed by Russian-speaking threat actors. Overall, its modular architecture and advanced stealth capabilities make it an attractive post-exploitation tool for both cyber-espionage and financially motivated operations. Security researchers have observed Skitnet being used in the wild by several ransomware groups, notably in Microsoft Teams phishing campaigns attributed to BlackBasta, as well as in attacks involving the Cactus ransomware. These real-world deployments underscore Skitnet’s growing role as a versatile and persistent foothold in sophisticated attack chains.
Suggested Corrections:
Users should always be cautious of individuals or organizations that ask for personal information. Most companies will not ask for sensitive data from their customers. If in doubt, users should verify with the company itself to avoid any potential issues.
Users should always take a close look at the sender’s display name when checking the legitimacy of an email. Most companies use a single domain for their URLs and emails, so a message that originates from a different domain is a red flag.
As a general rule, users should not click links or download files even if they come from seemingly “trustworthy” sources.
Check for mismatched URLs. While an embedded URL might seem perfectly valid, hovering above it might show a different web address. In fact, users should avoid clicking links in emails unless they are certain that it is a legitimate link.
Users should always be on the lookout for any grammatical errors and spelling mistakes. Legitimate companies will often employ proofreaders and editors who ensure that the materials they send out are error-free.
Users should not be frightened or intimidated by messages that have an alarmist tone. They should double check with the company if they are uncertain about the status of their accounts.
Phishing emails are designed to be sent to a large number of people, so they need to be as impersonal as possible. Users should check whether the message contains a generic subject and greeting, as this can be a sign of a phishing attempt.
Although not every end user has access to advanced anti-phishing software, they can still use the built-in protection of their email clients to filter messages. One example is setting the email client to block all images unless approved.
Legitimate companies will never send confirmation emails unless there are specific reasons for doing so. In fact, most companies will avoid sending unsolicited messages unless it’s for company updates, newsletters, or advertising purposes.
Users should always take the context of an email or message into account. For example, most online accounts do away with viewable member numbers, so users should be wary if they receive emails containing a “member number” for services that generally don’t use them.
It is important to take note of unusual information in the text of the message. Any mentions of operating systems and software that are not typically used by consumers can often be indicators of a phishing attempt.
If it seems suspicious, it probably is. Users should always err on the side of caution when it comes to sending out personally identifiable information through messages and emails.
Link(s):
https://www.bleepingcomputer.com/ne...singly-use-skitnet-post-exploitation-malware/
Skitnet is a highly modular and multi-stage malware strain attributed to the threat actor LARVA-306. It combines multiple programming languages, including Rust, Nim, PowerShell, and .NET, to maintain stealthy and persistent access to targeted systems. The initial stage, a Rust binary, decrypts and manually maps an embedded Nim payload using ChaCha20 encryption and the DInvoke-rs library for reflective code loading. This Nim binary establishes a DNS-based reverse shell by dynamically resolving APIs and crafting DNS queries to the C2 server. It then launches a cmd[.]exe process, with multiple threads handling DNS polling and encrypted communication. Skitnet’s command-and-control panel manages infected devices using C drive serial numbers as unique identifiers and enforces filters for geographic and network-based targeting. It also employs a Bash-based automated setup and cleans up forensic artifacts like SSH logs, command history, and IP traces, enhancing its operational stealth.
Once persistence is achieved, primarily through DLL hijacking of a signed Asus binary (ISP.exe) and PowerShell scripts, Skitnet enables several post-compromise capabilities via its control panel. Supported commands include ‘startup’ for persistence, ‘screen’ for screenshot capture (uploaded to Imgur), and ‘anydesk/rutserv’ for the silent deployment of legitimate remote access tools. Also supported is the ‘shell’ command, which enables real-time remote command execution via PowerShell and persistent polling for new tasks, as well as an ‘av’ command that is designed to collect installed security software information using WMI queries. A .NET-based loader extends Skitnet’s modularity, decoding and executing additional obfuscated payloads using RC4 decryption, where keys and parameters are embedded in environment variables. These secondary payloads connect to dynamically constructed C2 URLs for further instructions or malware downloads.
Security Officer Comments:
Skitnet has been actively marketed on underground forums such as RAMP since April 2024 and is believed to be developed and distributed by Russian-speaking threat actors. Overall, its modular architecture and advanced stealth capabilities make it an attractive post-exploitation tool for both cyber-espionage and financially motivated operations. Security researchers have observed Skitnet being used in the wild by several ransomware groups, notably in Microsoft Teams phishing campaigns attributed to BlackBasta, as well as in attacks involving the Cactus ransomware. These real-world deployments underscore Skitnet’s growing role as a versatile and persistent foothold in sophisticated attack chains.
Suggested Corrections:
Users should always be cautious of individuals or organizations that ask for personal information. Most companies will not ask for sensitive data from their customers. If in doubt, users should verify with the company itself to avoid any potential issues.
Users should always take a close look at the sender’s display name when checking the legitimacy of an email. Most companies use a single domain for their URLs and emails, so a message that originates from a different domain is a red flag.
As a general rule, users should not click links or download files even if they come from seemingly “trustworthy” sources.
Check for mismatched URLs. While an embedded URL might seem perfectly valid, hovering above it might show a different web address. In fact, users should avoid clicking links in emails unless they are certain that it is a legitimate link.
Users should always be on the lookout for any grammatical errors and spelling mistakes. Legitimate companies will often employ proofreaders and editors who ensure that the materials they send out are error-free.
Users should not be frightened or intimidated by messages that have an alarmist tone. They should double check with the company if they are uncertain about the status of their accounts.
Phishing emails are designed to be sent to a large number of people, so they need to be as impersonal as possible. Users should check whether the message contains a generic subject and greeting, as this can be a sign of a phishing attempt.
Although not every end user has access to advanced anti-phishing software, they can still use the built-in protection of their email clients to filter messages. One example is setting the email client to block all images unless approved.
Legitimate companies will never send confirmation emails unless there are specific reasons for doing so. In fact, most companies will avoid sending unsolicited messages unless it’s for company updates, newsletters, or advertising purposes.
Users should always take the context of an email or message into account. For example, most online accounts do away with viewable member numbers, so users should be wary if they receive emails containing a “member number” for services that generally don’t use them.
It is important to take note of unusual information in the text of the message. Any mentions of operating systems and software that are not typically used by consumers can often be indicators of a phishing attempt.
If it seems suspicious, it probably is. Users should always err on the side of caution when it comes to sending out personally identifiable information through messages and emails.
Link(s):
https://www.bleepingcomputer.com/ne...singly-use-skitnet-post-exploitation-malware/