QakBot’s infection chain

QakBot is distributed using spear-phishing emails (Figure 2) that contain Excel files with Excel 4.0 macros. The emails entice the recipient to enable macros, which download and execute the QakBot DLL files (Figures 3 and 4). The downloaded QakBot DLL is dropped onto a specific file path and file name, and is executed via regsvr32.exe (Figure 5). The QakBot DLL performs process injection using explorer.exe (Figure 6), after which the injected Explorer process creates a scheduled task to maintain the malware’s initial foothold in the infected system (Figure 7).

Once QakBot is installed in a system, it proceeds to download and drop the other components in the infection chain, beginning with the Cobeacon backdoor. We have observed the execution of Cobeacon using a fileless PowerShell script with multiple layers of obfuscation (Figures 8 to 11). The Base64-encoded shellcode of the installed Cobeacon establishes and names a pipe for communication (Figure 12) that is possibly used for exfiltration purposes once information has been collected from a targeted system. The Black Basta ransomware group posts this information on its leak sites if the victim does not pay the ransom.

PrintNightmare and Coroxy

Upon further analysis of the system that was affected by Black Basta, we found evidence that points to the ransomware group’s exploitation of the PrintNightmare vulnerability. Exploiting this vulnerability, Black Basta abused the Windows Print Spooler Service or spoolsv.exe to drop its payload, spider.dll, and perform privileged file operations. It also exploited the vulnerability to execute another file in the affected system, but samples of this file were no longer available in the system.

Additionally, our investigation found that the ransomware actors used the Coroxy backdoor. They used Coroxy in conjunction with the abuse of the computer networking utility tool Netcat to move laterally across the network. Once the attackers gained a wide foothold in the network, they executed the Black Basta ransomware, whose infection process we explained in more detail in a previous blog post.

Thwarting phishing attempts

Spear phishing is a common precursor to ransomware infection. Organizations can protect their data from threats that spread through emails by adhering to best practices such as:

• Ensuring that macros are disabled in Microsoft Office applications.
• Verifying an email’s sender and content before opening or downloading any attachments.
• Hovering the pointer over embedded links to show the links’ full addresses.
• Being wary of telltale signs of malicious intent, including unfamiliar email addresses, mismatched email and sender names, and spoofed company emails.

Businesses and their employees can safeguard sensitive company data from email-borne ransomware threats like Black Basta by turning to endpoint solutions such as Trend Micro’s Smart Protection Suites and Worry-Free Business Security solutions, which are equipped with behavior-monitoring capabilities that are able to detect malicious files, scripts, and messages, and block all related malicious URLs. Trend Micro™ Deep Discovery™ also has a layer for email inspection that protects businesses by detecting any malicious attachments and URLs. Multilayered detection and response solutions like the Trend Micro Vision One™ platform provides companies with greater visibility across multiple layers — like email, endpoints, servers, cloud workloads, and networks — to look out for suspicious behavior in their systems and block malicious components early, mitigating the risk of ransomware infection. 

URLs
24[.]178[.]196[.]44:2222
37[.]186[.]54[.]185:995
39[.]44[.]144[.]182:995
45[.]63[.]1[.]88:443
46[.]176[.]222[.]241:995
47[.]23[.]89[.]126:995
72[.]12[.]115[.]15:22
72[.]76[.]94[.]52:443
72[.]252[.]157[.]37:995
72[.]252[.]157[.]212:990
73[.]67[.]152[.]122:2222
75[.]99[.]168[.]46:61201
103[.]246[.]242[.]230:443
113[.]89[.]5[.]177:995
148[.]0[.]57[.]82:443
167[.]86[.]165[.]191:443
173[.]174[.]216[.]185:443
180[.]129[.]20[.]53:995
190[.]252[.]242[.]214:443
217[.]128[.]122[.]16:2222
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