Sophos Tracks Nefilim And Other Ransomware Attacks to “Ghost” Account Credentials

Sophos Press Release

OXFORD, U.K. – Jan. 26, 2021 – Sophos, a global leader in next-generation cybersecurity, today published its latest findings into real world attacks investigated by its Rapid Response team. The article, “Nefilim Ransomware Attack Uses ‘Ghost’ Credentials,” details how a failure to keep close tabs on “ghost” account credentials facilitated two recent cyberattacks, one of which involved Nefilim ransomware.

Nefilim, also known as Nemty ransomware, combines data theft with encryption. The target hit by Nefilim had more than 100 systems impacted. Sophos responders traced the initial intrusion to an admin account with high level access that attackers had compromised more than four weeks before they released the ransomware. During this time, the attackers were able to quietly move through the network, steal credentials for a domain admin account, and find and exfiltrate hundreds of GB of data, before unleashing the ransomware that revealed their presence.

The hacked admin account that enabled this belonged to an employee who had sadly passed away around three months previously. The company had kept the account active because it was used for a number of services.

In the second, unrelated attack, Sophos responders found that intruders had created a new user account and added it to the target’s domain admin group in Active Directory. With this new new domain admin account, the attackers were able to delete approximately 150 virtual servers and encrypt the server backups using Microsoft Bitlocker – all without setting off alerts.

“If it wasn’t for the ransomware that flagged the presence of intruders, how long might the attackers have had domain admin access to the network without the company knowing?” said Peter Mackenzie, manager, Sophos Rapid Response. “Staying on top of account credentials is basic, but critical cybersecurity hygiene. We see far too many incidents where accounts have been set up, often with considerable access rights, that are then forgotten about, sometimes for years. Such ‘ghost’ accounts are a prime target for attackers.

“If an organization really needs an account after someone has left the company, they should implement a service account and deny interactive logins to prevent any unwanted activity. Or, if they don’t need the account for anything else, disable it and carry out regular audits of Active Directory.

“The danger is not just keeping outdated and unmonitored accounts active; it is also giving employees greater access rights than they need. Fewer accounts need to be a domain admin than most people think. No account with privileges should be used by default for work that doesn't require that level of access. Users should elevate to using the required accounts when needed and only for that task. Further, alerts should be set so that if the domain admin account is used or if a new admin account is created, someone knows.” 

Nefilim ransomware was first reported on in March 2020. Like other ransomware families such as Dharma, Nefilim mainly targets vulnerable Remote Desktop Protocol (RPD) systems as well as exposed Citrix software. It is one of a growing number of ransomware families, alongside DoppelPaymer and others that engages in so-called “secondary extortion,” with attacks that combine encryption with data theft and the threat of public exposure.

Further information on the incidents, including Indicators of Compromise (IoCs) and tactics, techniques and procedures (TTPs) for the Nefilim attack, can be found in “Nefilim Ransomware Attack Uses ‘Ghost’ Credentials.

Ransomware timeline



About Sophos

Sophos is a worldwide leader and innovator of advanced cybersecurity solutions, including Managed Detection and Response (MDR) and incident response services and a broad portfolio of endpoint, network, email, and cloud security technologies that help organizations defeat cyberattacks. As one of the largest pure-play cybersecurity providers, Sophos defends more than 500,000 organizations and more than 100 million users globally from active adversaries, ransomware, phishing, malware, and more. Sophos’ services and products connect through its cloud-based Sophos Central management console and are powered by Sophos X-Ops, the company’s cross-domain threat intelligence unit. Sophos X-Ops intelligence optimizes the entire Sophos Adaptive Cybersecurity Ecosystem, which includes a centralized data lake that leverages a rich set of open APIs available to customers, partners, developers, and other cybersecurity and information technology vendors. Sophos provides cybersecurity-as-a-service to organizations needing fully-managed, turnkey security solutions. Customers can also manage their cybersecurity directly with Sophos’ security operations platform or use a hybrid approach by supplementing their in-house teams with Sophos’ services, including threat hunting and remediation. Sophos sells through reseller partners and managed service providers (MSPs) worldwide. Sophos is headquartered in Oxford, U.K. More information is available at www.sophos.com.