It has been observed that the variants of a new ransomware named as "cerber" are spreading widely. The malware is capable of infecting Windows operating system by encrypting filesof specific extensions present on the victims┐ machine and thereafter making it unusable for the user. The malware propagates itself via social engineering techniques, exploiting ADOBE FLASH player vulnerability CVE-2016-1019, or by means of web compromised malware propagation mechanism like in case of "AMMYY Admin" compromised website spreading the "CERBER3" ransomware. Social engineering techniques used for propagation includes spam emails containing malicious attachments with subjects like "confirmation of an online e-commerce order", "purchase or package shipment", drive-by-download attacks, specially crafted URLs in emails.
The malware is capable of performing the following functions:
- Encrypts the specific files of the victim's machine.
- Make network connections to the call back server to send uniquely identifiable system information.
- Make file system and registry changes such as installation of specific windows themes representing ransomware encryption.
- Make use of native Windows utilities such as WMIC and/or VSSAdmin to delete backups and shadow copies.
- Add file extension to the encrypted files such as .cerber. .cerber2, .cerber3, and some variants also add extension randomly.
- Capable of keeping persistence by creating command processor, screensaver, startup.run and runonce registry entries.
- Delays actual payload execution for encryption to avoid detection by antivirus solutions.
- Capable of encrypting the database running on the targeted machine by identifying the DB processes and if found any, it first kills those processes and then try to encrypt the database.
Aliases:Trojan.Ransom.Cerber [ALYac], Win.Trojan.Cerber-1 [ClamAV], TrojWare.Win32.Ransom.Cerber.~A [Comodo], Win32/Filecoder.Cerber.A [ESET-NOD32], Ransom.Cerber [Malwarebytes], Ransom:Win32/Cerber.A [Microsoft], Ransom.Cerber [Symantec], Trojan/Filecoder.Cerber.a [TheHacker], Trojan/W32.Cerber.176128 [nProtect]
Indicator of compromise:
File system Changes:
Upon execution, it copies itself at the following location:
It creates the following registry entries to execute itself at windows starts:
Upon Execution, the ransomware make file system changes and simultaneously encrypts specific files of the victim┐s machine. The file extensions targeted by the malware for encryption are:
Once the encryption is successful, it drops 3 files on the victim┐s machine and simultaneously change the desktop wallpaper of the infected machine. The files created by the malware are mentioned in "File system changes" section.
The screen shown to the user after encryption is:
In the figure shown above, the highlighted string is the unique identifier for the system infected with cerber ransomware.
Content of the dropped files contains a step-by-step procedure for paying the ransom and get the decryption key for the encrypted files. The content of the file is shown below:
Content of the encrypted files:
VM Detection Mechanism:
The malware is capable of checking the Virtual Machine environment by searching VM specific file names and paths, hooked modules, known sandbox volume serial numbers, including: sbiedll.dll, dir_watch.dll, api_log.dll, dbghelp.dll, Frz_State, C:\popupkiller.exe, C:\stimulator.exe, C:\TOOLS\execute.exe, \sand-box\, \cwsandbox\, \sandbox\, 0CD1A40, 6CBBC508, 774E1682, 837F873E, 8B6F64BC.
The following code snippet compares the subkey name with the VBox vendor ID.
Checking the VBox vendor ID.
The command and control server used by the cerber ransomware in some cases is:
- Apply software restriction policies depending upon the operating system installed. Details are given below:
Windows XP Path : %UserProfile%\Local Settings\*.exe
Windows Vista/7/8 Path : %LocalAppData%\*.exe
Security Level: Disallowed
Description: Don't allow executables to run from %AppData%.
- Conductroutine backups of important files, keeping the backups stored offline.
- Disconnect the infected system from wireless or wired networks to prevent the malware from further encrypting files stored over network shares.
- Exercise caution while visiting links within emails received from untrusted users or unexpectedly received from trusted users.
- Do not download and open attachments in emails received from untrusted users or unexpectedly received from trusted users.
- Exercise caution while visiting links to web pages.
- Protect yourself against social engineering attacks.
- Do not visit untrusted websites.
- Enable firewall at desktop and gateway level and disable ports that are not required.
- Avoid downloading pirated software.
- Keep up-to-date patches and fixes on the operating system and application software.
- Keep up-to-date antivirus and antispyware signatures at desktop and gateway level.
- Ensure that programs and users of the computer use the lowest level of privileges necessary to complete a task. When prompted for a root or UAC password, ensure that the program asking for administration-level access is a legitimate application.
- Disable AutoPlay to prevent the automatic launching of executable files on network and removable drives, and disconnect the drives when not required. If write access is not required, enable read-only mode if the option is available.
- Turn off file sharing if not needed. If file sharing is required, use ACLs and password protection to limit access. Disable anonymous access to shared folders. Grant access only to selected user accounts with strong passwords. Enable access on need basis.
- Turn off and remove unnecessary services. By default, many operating systems install auxiliary services that are not critical. These services are avenues of attack. If they are removed, threats have less avenues of attack.
- Configure your email server to block or remove email that contains file attachments that are commonly used to spread threats, such as .vbs, .bat, .exe, .pif and .scr files.
- Isolate compromised computers quickly to prevent threats from spreading further. Perform a forensic analysis and restore the computers using trusted media and trusted backups.
- If Bluetooth is not required for mobile devices, it should be turned off. If you require its use, ensure that the device's visibility is set to "Hidden" so that it cannot be scanned by other Bluetooth devices. If device pairing must be used, ensure that all devices are set to "Unauthorized", requiring authorization for each connection request. Do not accept applications that are unsigned or sent from unknown sources.