Self Assessment


Published On : 2021-12-30
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BigLock is a ransomware discovered in 2020 and also known as “corona-lock.” It encrypts files on the victim system with chacha and AES encryption as specified by the ransomware authors in the ransom note. All encrypted files are appended with “.corona-lock” extension. The malware took advantage of the corona pandemic period by tricking people to open malicious documents with a name like “CORONA TREATMENT.doc” file distributed as an email attachment which is carrying malicious ransomware payload. The malware is spread through spam emails having subject line as “Corona Virus Cure for China or Italy”. Upon execution, the malware modifies registry entries and injects malicious code among boot-up files. After encryption, the ransom-note “README_LOCK.txt” dropped on the desktop and other folders.

The ransom notes state that the data has been encrypted and the algorithm used for encryption are cha and AES. Further, the victims are warned not to use any third-party software or decryption tools. To recover encrypted data the ransom note mentions an email-id to contact malware authors.

Risk Score: 8
Confidence Level: High.
Suspected Malware: BigLock Malware.
Function: Ransomware.
Threat actor Associations:
Other Malware related to BigLock: CovidWorldCry Ransomware, CoronaLock Ransomware.
First Seen: May 2020.

BigLock Ransomware Analysis:

File Details: As shown in Figure1 and Figure3, the following are the details related to the ransomware “BigLLock”.
File Type: Windows PE-32 Executable
MD5: d82b27fdcc3a63f2ab0c46c5a3caef0a
SHA256: 746c79b5b6030091c37251939690eee31d023de5303544b46032bf89580806e5
Subsystem: GUI
Compilation Time: March 2019


C/C++ based and is PE-32 executabl malware

As shown in Figure1 above the malware is Visual C/C++ based and is PE-32 executable. Further, Figure2 below specifies that the malware is packed.


Packed malware

Figure3 below shows the hashes corresponding to the ransomware and shows that the file has a GUI subsystem and compilation timestamp of 28 March 2019 that is the time when the corona (covid-19) pandemic starts.


GUI subsystem and compilation timestamp

Figure4 below shows that how the ransomware is detected as malicious by different anti-malware solutions and some specifically mentioned it related to ransom activity (see highlighted part in Figure4 below).


ransomware is detected by antimalware solution

Figure5 below shows the sections present in the malware and looking quite normal except the .data section which has a large difference in its raw and virtual size and may contain some malicious packed code.


sections present in the malware

Figure6 below shows the libraries imported by the malware and indicated some of the functionality which it carries which includes low-level functionality to handle memory and devices, the functionality of handling graphical user interface, and other user-interface components.


libraries imported by the malware

Figure7 below shows the APIs imported by the ransomware and indicate the following functionality/capability in the malware:

  • Multiple Anti-debugging capabilities.
  • Capability to collect system information.
  • Synchronization capability to handle multiple processes and threads and to access shared resources.
  • Capability to handle windows/GUI functions.
  • Capability to search Drives, Folders.
  • Capability to access registry entries and manipulate them.
  • Have the capability to access native APIs to perform low-level functions like handling/manipulation of hardware, memory, and processes directly.
  • Capability to create new threads and processes.
  • Dynamic memory allocation and manipulation capability.
  • Capability to load other DLLs, libraries, and processes in memory.
  • Capability to sleep or deactivate when want to hide.
  • Ability to handle, search, open, write, access, perform the operation, and manipulate files.
  • Ability to encrypt files.
  • Capability to handle command-line arguments/strings of the process.


APIs imported by the ransomware

Upon execution of the ransomware, it encrypts the file with the extension “.corona_lock”, for example, if the filename is “” after encryption the file name changed to “” as shown in Figure8 (highlighted in red) given below. It also excludes the file having some specific extension like .exe. .dll (see Figure8 highlighted part in green).


file having some specific extension like .exe

Figure 9 shows all the folders accessed by the ransomware.


folders accessed by the ransomware

Figure10 below shows the ransom note dropped by the ransomware on the victim machine. It specifies that the encryption used is the combination of ChaCha and AES encryption algorithms and the files encrypted were marked by extension “.corona-lock”. Further instructions are given to the victim not to use any decryption tools which results in loss of data permanently and not contact any third party like data recovery companies. One email-Id “[email protected]” is also mentioned to contact malware authors for getting decryption key. Each victim user has been assigned a unique id as specified in the ransom note below in Figure10. The malware authors instructed that during correspondence the victim must specify this unique id. The ransom notes also specify a long list of files encrypted by the ransomware.


ransom note dropped by the ransomware on the victim machine

Figure11 below shows the process tree corresponding to ransomware execution. As shown at point1, the malware unpacks the packed code and uses process hollowing to replace the process with a new malicious process with the same name. After that the malware deletes the shadow volume copies by three different methods, In the first method as shown in Figure11 (at point 2 ), the malware tries to remove the shadow copies by resizing them by using the vssadmin.exe utility available in windows. This method of resizing diff areas to remove shadow copies is relatively new in ransomware families. Similarly in 2nd method at point 3 it used the same utility “vssadmin.exe” to delete the shadow copies by executing the command: “vssadmin.exe Delete Shadows /All /Quiet” and in the 3rd method (as shown at point 4), the ransomware used the “wmic.exe” utility of windows to delete the shadow copies as “wmic.exe SHADOWCOPY /nointeractive”. The methods 2nd and 3rd are quite popular among ransomware families to delete the shadow volume copies so that the victim can’t be able to recover the encrypted files. At last, as shown in Figure11 (point5), the malware tries to delete the ransomware executable from the system.



process tree corresponding to ransomware execution.

Figure12 below shows some snippets of registry access by the ransomware. Here the highlighted part shows that the malware tries to gain persistence by modifying registry entries.


snippets of registry access by the ransomware

MITRE Attack Tactics and Techniques:


Sr No. Tactic Technique
1 Initial Access (TA0001) T1566 Phishing
2 Execution (TA0002) T1204.002 Malicious File
3 Persistence (TA0003) T1547.001 Registry Keys
4 Defense Evasion (TA0005) T1112 Modify Registry
T1497.003 Time-Based Evasion
T1055.012 Process Hollowing
5 Discovery (TA0007) T1082 System Information Discovery
6 Impact (TA0040) T1486 Data Encrypted


List of IOCs:

Sr No. Indicator Type Remarks
1 d82b27fdcc3a63f2ab0c46c5a3caef0a Hash MD5
2 746c79b5b6030091c37251939690eee3
Hash SHA256
3 4e6569aeb368883e10afe84c04a19567c3d
Hash SHA512


  1. Implement a complex password policy with renewal at regular intervals.
  2. Implement a Multifactor Authentication policy.
  3. Regularly update all software on all systems and networks and other devices and turn on automatic updates if possible.
  4. Implement a Role-Based access policy and restrict it to minimal as per the requirement.
  5. Implement an Internal threat management policy that includes, train and educate employees about the latest threats and ransomware attacks and how to behave in such scenarios.
  6. Restrict to click or open suspicious/unauthorized links and files, specifically on organization devices.
  7. Must implement regular back-ups policy, more than one backup, and kept one on a separate network and other isolated offline at a different place.
  8. Use best IDS/IPS, firewall, and another antivirus/anti-spam/anti-ransomware and anti-malware solutions.
  9. Regular audits are necessary from a third party.
  10. Regular vulnerability assessment and patching policy.