Posts Tagged Ransomware

The New Ryuk Ransomware Attack

Ryuk is a type of crypto-ransomware. It uses encryption as a way to block access to a system or file until the ransom is paid. The ransomware is generally dropped with the help of other malware such as TrickBot or Emotet. Another mode of infection used by Ryuk ransomware is ‘Remote Desk Services’.

The Ryuk attacks were popular in third quarter of 2019, however the ransomware went silent at the onset of COVID-19 quarantine. But, it has returned as new Ryuk ransomware with added features and evolution of tools used to compromise target networks and ransomware deployment.

The most notable feature of new Ryuk ransomware is ‘Speed’. Once a system is infected, the attackers gain access of domain controller and enter early stage of deployment just within a day.

The second notable feature of new Ryuk ransomware is ‘Persistence’. The attackers make multiple attempts by sending renewed phishing emails to establish a contact.

How Is A System Infected?

  • The attackers send a phishing email to the target. The email contains a link, which redirects the user to a malicious document hosted on ‘docs.google.com’.
  • When a user opens the document, its contents are enabled. This allows the document to execute a malicious executable identifier ‘print_document.exe’ as a Buer Loader. Buer Loader is a modular malware-as-a-service downloader.
  • When executed, Buer Loader drops malware files and a Cobalt Strike beacon ‘qoipozincyusury.exe’. it is a modular attack tool which is capable of performing multiple tasks such as providing access to operating system features and establishing a covert command & control channel within the compromised network.
  • Additional Cobalt Strike beacons are downloaded on the system for reconnaissance and to hunt for credentials. Numerous commands are run on the infected system to retrieve information such as list of trusted domains, list of members of ‘enterprise admins’, list of administrators for local machine, list of domain admins, network configuration, etc.
  • Using this data, attackers obtain administrative credentials and connect to domain controller, where they dump data of Active Directory.
  • Using domain administrator credentials, another Cobalt Strike service is installed on the domain controller. It is a chained Server Message Block listener. It allows Cobalt Strike commands to be passed on to the server and other computers on the network. This allows attackers to spread the attack laterally onto other systems in the same network.
  • The Ryuk is launched and it attacks the backup server. In case of detection or interruption by security protocols, the attackers use icacls command to modify access control. This gives them complete control of the system folders on the server.
  • Now, they deploy GMER, a rootkit detector tool. It is used to find and shutdown hidden processes such as antivirus. The ransomware is re-deployed and re-launched multiple times to overwhelm remaining defenses.
  • Ransom notes are dropped in folders hosting the ransomware.

Educate the employees to refrain from opening doubtful emails and documents to prevent the new Ryuk attack.

For more information on the new Ryuk ransomware attack, contact Centex Technologies at (254) 213 – 4740.

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What Is CryptoWall Ransomware?

A ransomware is a type of malware that encrypts user files on victim computer or network. The attacker then demands a ransom from the victim in exchange for the decryption key. CryptoWall is a family of such file-encrypting ransomware. It first appeared in early 2014 and has numerous variants including Cryptorbit, CryptoDefense, CryptoWall 2.0, and CryptoWall 3.0. The early variants used RSA public key for file encryption, however, the new versions use AES key for file encryption. The AES key is further encrypted using a public key. This makes it impossible to get the actual key needed to decrypt the files.

Mode Of Infection:

Traditionally, CryptoWall ransomware was distributed via exploit kits. But, now spam emails are also used to infect the victims. The spam email contains RAR attachment that includes a CHM file. When the victim opens the CHM file, it downloads ‘CryptoWall binary’ to the system and copies itself into the %temp% folder.

CHM file – Compiled HTML or CHM file is an interactive html file that is compressed inside a CHM container and may hold other files such as JavaScript, images, etc. inside it.

Execution:

  • The Cryptowall binary downloaded on the system is compressed or encoded. Useless instructions and anti-emulation tricks are deliberately inserted in the coding to break AV engine protection.
  • On execution, it launches a new instance of explorer.exe process.
  • In the next step, the ransomware injects its unpacked CrytoWall binary and executes the injected code.
  • The original process automatically exits itself after launching the injected explorer process.
  • The files are encrypted and the ransomware deletes the volume shadow files using ‘vssadmin.exe’ tool. This makes sure that the encrypted files may not be recovered.
  • The CryptoWall binary is copied to various locations such as %appdata%, %startup%, %rootdrive%, etc. The copies are added to the auto start key to help them stay persistent even after the infected system is rebooted.
  • A new svchost.exe process is launched with user privilege and malicious binary code is injected into it.
  • The ransomware connects to I2P proxies to find live command and control server.
  • The server replies with unique encryption key generated specifically for the target system. The key starts the file encryption thread and drops ransom notes in all directories.
  • Finally, it launches Internet Explorer to display ransom notes and the hollowed svchost process kills itself.

Protection:

  • Keep antivirus up-to-date
  • Back up the files
  • Apply windows update regularly
  • Avoid clicking random emails
  • Disable remote desktop connections
  • Block binaries running from %appdata% and %temp% paths

For more information on Cryptowall ransomware, contact Centex Technologies at (254) 213 – 4740.

 

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Understanding The Concept Of Ransomware As A Service

Ransomware is a type of malware that extorts money from the target victim by infecting and taking control of the victim’s systems or secured documents stored in the system. Ransomware attacks either locks the computer from normal use or encrypts the documents using a key available with the attacker only.  ‘Ransomware as a Service’ is a kind of ‘Software as a Service’ provided by tech vendor. RaaS can also be defined as a ransomware infrastructure that is rented to hackers on dark web. It is an easy platform for novice hackers (with zero to low knowledge of coding malware) to access ransomware attacks and implant these ransomwares on victim’s machines for claiming extortion money.

How Does RaaS Function?

Here is a simple map of events to explain the functioning of RaaS model:

  • A deceitful vendor offers a tool containing Ransomware on Dark web
  • The package contains all the software and related files needed for a successful ransomware attack
  • Hackers and malicious actors purchase this tool package
  • They use the tools for attacking a victim’s system or network to get hold of computer files and information
  • Depending upon the type of ransomware, it may either lock or encrypt the files
  • The hackers now demand financial ransom in exchange of returning data access to the victim

Similar to other ‘Software as a Service’ models, RaaS involves user services such as provision of desktop, infrastructure, ERP, customer relationship management or other digital services. The buyers of RaaS have the option to order up the capability of the ransomware for launching a more severe attack.

Some important points to note include:

  • RaaS users take deliberate steps to conceal their identity and take deliberate steps to make their actions hard to track. A common practice is to demand payments in digital currency as it is comparatively difficult to trace.
  • Once the victim makes the ransom payment, it is not guaranteed that the hacker will provide the decryption key to the victim. Also, making the ransom payment does not ensure that the hacker will not leak any files or documents.

What Measures Can Be Taken To Combat RaaS Attacks?

Organizations need to take following measures to secure themselves against RaaS attacks:

  • Employees are the most vulnerable entry point but they may be used as first line of defense, if properly educated. Regularly educate them on the latest ransomware attacks and cyber security practices they should employ.
  • Secure the system and network by continuously auditing for any vulnerability. Also, regularly update the cyber security tools for latest versions.
  • Maintain a backup of all the files at a location from where they can be easily retrieved. This helps the business to keep functioning even if the systems are attacked.

For more information on understanding the concept of ‘Ransomware as a Service’, contact Centex Technologies at (254) 213 – 4740.

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Necurs Botnet

PDF Version: Necurs-Botnet

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What Is SamSam Ransomware?

SamSam is a targeted ransomware attack which incorporates custom infection using a wide range of exploits or brute force tactics. The ransomware is also known as Samas or SamsamCrypt. The first version of the ransomware was released in late 2015. The SamSam ransomware attacks do not make use of phishing or malware downloads to infect a network; instead they utilize following modes of infection:

  • Vulnerabilities in Remote Desktop Protocols (RDP)
  • Vulnerabilities in Java based web servers
  • Vulnerabilities in File Transfer Protocol (FTP)
  • Brute force against weak passwords
  • Stolen login credentials

Once, the ransomware has initial foothold on the victim’s network, it compromises the network to gain control. Also, SamSam is a manual attack. Thus, in case an application detects the ransomware, the attackers modify a registry entry to disable the endpoint tool’s detection. This enables them to compromise the application and control the network. SamSam uses a number of applications to accomplish the attack such as Mimikatz, reGeorg, PsExec, PsInfo, RDPWrap, NLBrute, Impacket, CSVDE, PowerSploit and JexBoss.

During the reconnaissance phase, the attackers try to write a plain text file named test.txt to target. If successful, they add the target to a list titled alive.txt on Domain Controller (DC). After ensuring that DC has writing privileges for machines, the ransomware is deployed and pushed to all the machines controlled by DC simultaneously.

The ransomware follows an efficient approach for encrypting the files on infected machines.

  • The encryption is initiated on holidays, weekends or late nights to buy time for maximizing the impact before getting noticed.
  • Files with selective extensions or important files required for running the machines are encrypted first.
  • The remaining applications or files are encrypted later; starting from smaller files and gradually moving towards larger files.
  • A unique AES key is generated for every encrypted file.
  • As soon as encryption is complete, ransomware deletes its installer and removes any traces of the attack.
  • It becomes difficult for victims to download files from off shore backup because the applications required to run the machine are also inaccessible. Thus, they are required to go thorough time consuming process of reloading the disk and installing applications before downloading back up files.

A ransom note is left on target organization’s machines demanding a set amount of bitcoin currency to decrypt a single machine and a lump sum amount for decrypting all the machines at once. Every victim is provided a unique web address on dark web which leads to chat feature for communicating with the attackers. The chat is deleted after a victim pays the ransom.

Security Practices To Prevent SamSam Attack:

  • Regularly install available patches for RDP service. Also, disable the service when not needed by the users.
  • Ensure that no RDP ports are left open during interactions between cloud-based virtual machines and public IPs. If it is required to leave RDP Port of a system open, keep the system behind firewall and instruct users to communicate with this machine via VPN.
  • Enable, two-factor authentication, strong passwords and account lockout policies.

For more information on how to secure your network, call Centex Technologies at (254) 213 – 4740.

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