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Cuba Ransomware Hacked Microsoft Exchange Servers

The Cuba ransomware group doesn’t use any cloud services for the exfiltration step but instead sends everything onto their own private infrastructure.

 

To get early access to business networks and encrypt devices, the Cuba ransomware campaign is exploiting Microsoft Exchange vulnerabilities. The ransomware group is known as UNC2596, and the ransomware itself is known as COLDDRAW, according to cybersecurity firm Mandiant. 

Cuba is the most popular name for malware. Cuba is a ransomware campaign that began in late 2019, and while it started slowly, it gained traction in 2020 and 2021. In December 2021, the FBI issued a Cuba ransomware notice, stating that the group has infiltrated 49 critical infrastructure firms in the United States. Researchers indicate that the Cuba operation predominantly targets the United States, followed by Canada, according to a new analysis by Mandiant. Since August 2021, the Cuba ransomware gang has been using Microsoft Exchange vulnerabilities to launch web shells, RATs, and backdoors to gain a foothold on the target network. 

"Mandiant has also identified the exploitation of Microsoft Exchange vulnerabilities, including ProxyShell and ProxyLogon, as another access point leveraged by UNC2596 likely as early as August 2021," explains Mandiant in a new report. 

Cobalt Strike or the NetSupport Manager remote access tool is among the backdoors planted, although the organisation also utilises their own 'Bughatch', 'Wedgecut', 'eck.exe', as well as Burntcigar' tools. 
  • Wedgecut comes in the form of an executable named “check.exe,” which is a reconnaissance tool that enumerates the Active Directory through PowerShell.
  • Bughatch is a downloader that fetches PowerShell scripts and files from the C&C server. To evade detection, it loads in memory from a remote URL.
  • Burntcigar is a utility that can terminate processes at the kernel level by exploiting a flaw in an Avast driver, which is included with the tool for a “bring your own vulnerable driver” attack.
Finally, Termite is a memory-only dropper that downloads and loads the payloads mentioned earlier. However, this tool has been seen in campaigns by a variety of threat groups, indicating that it is not exclusively utilised by Cuba threat actors. 

Threat actors use stolen account credentials obtained with the widely available Mimikatz and Wicker tools to elevate access. They then use Wedgecut to undertake network reconnaissance before using RDP, SMB, PsExec, and Cobalt Strike to move laterally. Bughatch is then loaded by Termite, followed by Burntcigar, which disables security tools and creates the foundation for data exfiltration and file encryption. For the exfiltration process, the Cuba gang does not use cloud services, instead transfers everything to its own private infrastructure. 

Changing Operations 

Cuba ransomware teamed up with spammers behind the Hancitor malware in May 2021 to get access to corporate networks via DocuSign phishing emails. Since then, Cuba's operations have shifted to focus on vulnerabilities in public-facing services, such as the Microsoft Exchange ProxyShell and ProxyLogon flaws. Because security updates to fix the exploited vulnerabilities have been available for months, this move makes the assaults more potent but also easier to prevent. 

Once there are no more valuable targets running unpatched Microsoft Exchange servers, the Cuba operation will likely shift its focus to other vulnerabilities. This means that adopting accessible security updates as soon as they are released by software providers is critical in maintaining a strong security posture against even the most sophisticated threat actors.
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