Original Issue Date:-July 07, 2020
It has been reported that a new ransomware-as-a-service (RaaS) tool, called “Thanos” which provides buyers and affiliates a customization tool to build unique payloads, is spreading and gaining popularity among various underground forums and channels. This ransomware family employs the RIPlace tactics majorly used to bypass the anti-ransomware endpoint security.
Thanos ransomware primarily delivered via phishing emails. The attack campaign attracts the user with luring financial information like tax-refund details, invoice scheme etc. Upon launch the ransomware tries to terminate various security processes and system utilities to ensure thorough encryption.
Its originally advertised features in late 2019 includes auto update for builder tool, written in .NET, unique encryption keys per host , Anti-VM / VM-evasion, multiple persistence options and many more. Later RIPlace technique along with other updated features have been added during the last six months. Further noteworthy features are also added recently including disabling of 3rd party backup solutions (in addition to AV product termination), file-permission changing to capture (exfil) or encrypt more files, Bootlocker feature to display the ransom note at boot level (non UEFI / Secure Boot-protected clients), expanded support of encryption on Windows Server 2012 and many more to make it more resilient and sophisticated. This enhances threat potential of this Thanos ransomware.More than 80 Thanos “clients” are observed with different configurations options enabled. As observed, in Thanos ransomware builder, a user may select the option to enable RIPlace, which results in a modification of the encryption process workflow to use the technique.
Thanos’ encryption technique varies with the evolution of its payloads. While encrypting, Thanos uses a random, 32-byte string generated at runtime as a passphrase for the AES file encryption. The string is then encrypted with the ransomware operator’s public key and without the corresponding private key, recovering the encrypted files is extremely difficult / impossible.
However, the Thanos builder also provide feature to use a static password for the AES file encryption. In this option chosen, AES password used to encrypt files and if a Thanos client is recovered after the encryption has occurred then there is a chance of files recovery without paying ransom.
Countermeasures and Best practices for prevention:
- Don't open attachments in unsolicited e-mails, even if they come from people in your contact list, and never click on a URL contained in an unsolicited e-mail, even if the link seems benign. In cases of genuine URLs close out the e-mail and go to the organization’s website directly through browser.
- Install ad blockers to combat exploit kits such as Fallout that are distributed via malicious advertising.
- Prohibit external FTP connections and blacklist downloads of known offensive security tools.
- All operating systems and applications should be kept updated on a regular basis. Virtual patching can be considered for protecting legacy systems and networks. This measure hinders cybercriminals from gaining easy access to any system through vulnerabilities in outdated applications and software. Avoid applying updates / patches available in any unofficial channel.
- Restrict execution of Power shell /WSCRIPT in an enterprise environment. Ensure installation and use of the latest version of PowerShell, with enhanced logging enabled. Script block logging and transcription enabled. Send the associated logs to a centralized log repository for monitoring and analysis.
- Establish a Sender Policy Framework (SPF) for your domain, which is an email validation system designed to prevent spam by detecting email spoofing by which most of the ransomware samples successfully reaches the corporate email boxes.
- Application whitelisting/Strict implementation of Software Restriction Policies (SRP) to block binaries running from %APPDATA% and %TEMP% paths. Ransomware sample drops and executes generally from these locations.
- Users are advised to disable their RDP if not in use, if required, it should be placed behind the firewall and users are to bind with proper policies while using the RDP.
- Block the attachments of file types, exe|pif|tmp|url|vb|vbe|scr|reg|cer|pst|cmd|com|bat|dll|dat|hlp|hta|js|wsf
- Consider encrypting the confidential data as the ransomware generally targets common file types.
- Perform regular backups of all critical information to limit the impact of data or system loss and to help expedite the recovery process. Ideally, this data should be kept on a separate device, and backups should be stored offline.
- Network segmentation and segregation into security zones - help protect sensitive information and critical services. Separate administrative network from business processes with physical controls and Virtual Local Area Networks.