New Ymir Ransomware Partners With RustyStealer in Attacks

Summary:
Ymir, a relatively new ransomware family, has been observed by researchers at Kaspersky encrypting systems that were previously compromised by RustyStealer, an infostealer malware first documented in 2021. Ymir ransomware initiated operations in July 2024 and is known for its in-memory execution, use of PDF files as ransom notes, and extension configuration options. The group’s encryptor is designed to target Windows systems and uses the ChaCha20 stream cipher, an advanced and fast encryption algorithm, to encrypt files on the victim's systems. Encrypted files are typically appended with a random extension such as ".6C5oy2dVr6.” As noted above the ransomware strain operates entirely from memory, employing functions like 'malloc,' 'memove,' and 'memcmp,' to evade detection. It’s also capable of detecting whether it’s running within a sandbox environment by identifying running processes, checking the system uptime, etc. Ymir currently does not have a data leak site. However, as seen with other ransomware groups, it won’t be long before the group engages in exfiltration schemes, threatening to publish stolen data online if a ransom is not paid by the victim.

Security Officer Comments:
The emergence of Rusty Stealer underscores a growing trend of cybercriminals collaborating in sophisticated, coordinated operations. In a series of attacks tracked by Kaspersky, systems previously encrypted by Ymir ransomware were infiltrated by Rusty Stealer just two days prior to the ransomware deployment. This timing suggests a close relationship between the operators of Rusty Stealer and Ymir ransomware. Rusty Stealer is particularly effective at harvesting credentials and other sensitive data, enabling attackers to gain unauthorized access to high-privilege accounts, further facilitating lateral movement across the network. By leveraging Rusty Stealer, Ymir ransomware operators can streamline their attacks, significantly reducing the time spent on gaining initial access to victim environments. This allows them to concentrate their efforts on encrypting data across multiple systems, facilitating larger-scale extortion campaigns through ransom demands.

Suggested Corrections:
Backup your data, system images, and configurations, regularly test them, and keep the backups offline:
Ensure that backups are regularly tested and that they are not connected to the business network, as many ransomware variants try to find and encrypt or delete accessible backups. Maintaining current backups offline is critical because if your network data is encrypted with ransomware, your organization can restore systems.

Update and patch systems promptly: This includes maintaining the security of operating systems, applications, and firmware in a timely manner. Consider using a centralized patch management system; use a risk-based assessment strategy to drive your patch management program.

Test your incident response plan: There's nothing that shows the gaps in plans more than testing them. Run through some core questions and use those to build an incident response plan: Are you able to sustain business operations without access to certain systems? For how long? Would you turn off your manufacturing operations if business systems such as billing were offline?

Check Your Security Team's Work: Use a 3rd party pen tester to test the security of your systems and your ability to defend against a sophisticated attack. Many ransomware criminals are aggressive and sophisticated and will find the equivalent of unlocked doors.

Segment your networks: There's been a recent shift in ransomware attacks – from stealing data to disrupting operations. It's critically important that your corporate business functions and manufacturing/production operations are separated and that you carefully filter and limit internet access to operational networks, identify links between these networks, and develop workarounds or manual controls to ensure ICS networks can be isolated and continue operating if your corporate network is compromised. Regularly test contingency plans such as manual controls so that safety-critical functions can be maintained during a cyber incident.

Train employees:
Email remains the most vulnerable attack vector for organizations. Users should be trained on how to avoid and spot phishing emails. Multi-factor authentication can help prevent malicious access to sensitive services.

Link(s):
https://www.bleepingcomputer.com/ne...omware-partners-with-rustystealer-in-attacks/