Welcome to the VMRay Malware Analysis Report Recap. Every month our Research Team provides a recap of the malware analysis reports posted to the VMRay Twitter account. This past December, our team analyzed a variant of Globeimposter ransomware, a Windows Script File (WSF) that downloads a payload to set-up a server to accept incoming connections and an RTF document that takes advantage of the CVE-2017-11882 vulnerability.
Click the links below to jump to a specific report:
- Globeimposter Ransomware Delivered via Necurs Botnet
- WSF Downloads a Payload that Sets-up a Server to Accept Incoming Connections
- RTF Document Takes Advantage of CVE-2017-11882 Vulnerability
Report Name: Globeimposter Ransomware Delivered via Necurs Botnet
December 5, 2017
This variant of Globeimposter ransomware was downloaded and executed by a malicious Visual Basic script. The script most likely was sent by the Necurs Botnet as an email attachment. The first action of the script is to contact its C&C (command and control server). From the Network Behavior tab of the report, we can see that the C&C was located in Houston, TX (Figure 1). After downloading the payload, the Globeimposter ransomware is executed.
Globeimposter then proceeds to encrypt the user’s files and leaves a ransom note with payment instructions. The ransom note is called “Read_ME” and is left on the desktop (Figure 2).
The cybercriminals offer free decryption of a single file as proof they have working decryption keys. Like other ransomware, Globeimposter deletes snapshots created by the Volume Shadow Copy Service to make it more unlikely that the user will be able to restore the encrypted files if there are no other backups.
December 13, 2017
The Windows Script File (WSF) downloads and executes a malicious file from a blacklisted URL (Figure 5). The payload uses common techniques like process injection (Figure 4) and writing itself into the Windows startup for persistence. All of the detected threats can be seen in the VTI tab of the report (Figure 3).
What stands out in this analysis is that it executes several processes. Shown in Figure 4, it adds Chakmcat.exe to the Windows startup folder for persistence (surviving a reboot). The malware injects into explorer.exe and runtimebroker.exe, which starts a local TCP Server on a dynamic port.
Upon the initial post of this report, Twitter user @markwo responded to our Tweet asking why we show a TCP server listening on port 0.
Tcp server listening on port 0? Do you grab the actual dynamic port that was bound? Seems odd for a backdoor, unless the port info is sent to C2
— Mark Wodrich (@markwo) 14 December 2017
This is not incorrect behavior. In our analysis, you can see all necessary information:[0082.882] socket (af=2, type=1, protocol=0) returned 0xd60
[0082.882] htonl (hostlong=0x7f000001) returned 0x100007f
[0082.882] bind (s=0xd60, addr=0x59df808*(sa_family=2, sin_port=0x0, sin_addr=”127.0.0.1″), namelen=16) returned 0
[0082.882] listen (s=0xd60, backlog=1) returned 0
[0082.882] socket (af=2, type=1, protocol=0) returned 0x2108
[0082.882] getsockname (in: s=0xd60, name=0x59df818, namelen=0x59df800 | out: name=0x59df818*(sa_family=2, sin_port=0xc116, sin_addr=”127.0.0.1″), namelen=0x59df800) returned 0
[0082.882] connect (s=0x2108, name=0x59df818*(sa_family=2, sin_port=0xc116, sin_addr=”127.0.0.1″), namelen=16) returned 0
The bind API call uses sin_port=0x0 to let the OS choose an appropriate port for the socket from the dynamic client port range (value between 49152 and 65535). Later, the getsockname API call is used to get the port that has been assigned to the socket (sin_port=0xc116 = 49430).
But as a response to @markwo’s question, we’ve updated our reports to include the actual port that the OS chooses for the socket rather than displaying ‘0’. You can see the updated report below.
December 20, 2017
The CVE-2017-11882 vulnerability exploits a 17-year-old component of Microsoft Office, the Microsoft Equation Editor. The Process Graph in Figure 7 shows the Equation Editor (eqnedt32.exe) which is exploited by the RTF Document. The Equation Editor is an attractive process for attackers because CVE-2017-11882 is easily exploitable due to the lack of enabled exploit mitigations like ASLR and DEP in the Equation Editor.
The RTF Document’s payload uses typical malware techniques like process injection and anti-analysis to try to detect an attached debugger as seen in the Detected Threats section in the VTI tab (Figure 8). The exploit’s shellcode downloads a known malicious file (lambdoidtegument.exe), drops it and then executes it.