OXFORD, U.K.  — février 23, 2022 —

Sophos, a global leader in next-generation cybersecurity, today released new research, “Dridex Bots Deliver Entropy in Recent Attacks,” that details code similarities in the general purpose Dridex botnet and the little-known ransomware, Entropy. The similarities are in the software packer used to conceal the ransomware code, in the malware subroutines designed to find and obfuscate commands (API calls), and in the subroutines used to decrypt encrypted text.

Sophos uncovered the similarities while investigating two incidents where attackers used Dridex to deliver Entropy ransomware. These attacks targeted a media company and a regional government agency, using specially crafted, customized versions of the Entropy ransomware dynamic link library (DLL) with the target’s name embedded in the ransomware code. In both attacks, the attackers also deployed Cobalt Strike on some of the targets’ computers and exfiltrated data to cloud storage providers using the legitimate WinRAR compression tool, before launching the ransomware on unprotected computers.

“It’s not unheard of for malware operators to share, borrow or steal each other’s code, either to save themselves the effort of creating their own, intentionally mislead attribution or distract security researchers. This approach makes it harder to find evidence that corroborates a ‘family’ of related malware or to identify ‘false flags’ that can make attackers’ jobs easier and investigators’ jobs harder,” said Andrew Brandt, principal researcher at Sophos. “In this analysis, Sophos focused on aspects of the code that both Dridex and Entropy apparently used to make forensic analysis more challenging. These include the packer code, which prevents easy static analysis of the underlying malware, a subroutine that the programs use to conceal the command (API) calls they make, and a subroutine that decrypts encrypted text strings embedded within the malware. The researchers found that the subroutines in both malware have a fundamentally similar code flow and logic.”

Different Attack Methodology

In addition to finding similarities in the code, Sophos researchers found some notable differences. In the attack on the media organization, the adversaries used the ProxyShell exploit to target a vulnerable Exchange server to install a remote shell they later leveraged to spread Cobalt Strike beacons to other computers. The attackers were in the network for four months before launching Entropy at the beginning of December 2021.

In the attack on the regional government organization, the target was infected with Dridex malware through a malicious email attachment. The attackers then used Dridex to deliver additional malware and move laterally within the target’s network. The incident analysis shows that approximately 75 hours after the initial detection of a suspicious login attempt on a single machine, the attackers started to steal data and move it to a series of cloud providers.

Staying Protected

The investigation found that in both cases, the attackers were able to take advantage of unpatched and vulnerable Windows systems and abuse legitimate tools. Regular security patching and the active investigation of suspicious alerts by threat hunters and security operations teams will help to make it harder for attackers to gain initial access to a target and deploy malicious code.

Sophos endpoint products, such as Intercept X, protect users by detecting the actions and behaviors of ransomware and other attacks, such as those described in this Sophos research. 

For further information, read the article “Dridex Bots Deliver Entropy in Recent Attacks.”

À propos de Sophos

Sophos est un leader mondial et un innovateur dans le domaine des solutions de cybersécurité avancées, qui comprend des services managés de détection et réponse (MDR) et de réponse aux incidents, ainsi qu’un vaste portefeuille de technologies de sécurité qui protègent les systèmes endpoint, les réseaux, les messageries et le Cloud contre les cyberattaques. Sophos est l’un des plus grands fournisseurs de cybersécurité et protège aujourd’hui plus de 500 000 entreprises et plus de 100 millions d’utilisateurs dans le monde contre les adversaires actifs, les ransomwares, le phishing, les malwares, etc. Les services et produits de Sophos sont connectés à travers sa console d’administration Sophos Central basée dans le Cloud et sont alimentés par Sophos X-Ops, l’unité de renseignement sur les menaces transversale de la société. L’intelligence de Sophos X-Ops optimise l’ensemble de l’écosystème de cybersécurité adaptatif (ACE) de Sophos, qui comprend un datalake centralisé exploitant un ensemble riche d’API ouvertes à destination des clients, des partenaires, des développeurs et des autres fournisseurs de cybersécurité et de technologies de l’information. Sophos fournit des services de cybersécurité aux entreprises qui ont besoin de solutions de sécurité clés en main et entièrement gérées. Les clients peuvent également gérer leur cybersécurité directement avec la plateforme d’opérations de sécurité de Sophos ou utiliser une approche hybride en complétant leurs équipes internes avec les services de Sophos, notamment la chasse aux menaces et la remédiation. Sophos vend ses produits par l’intermédiaire d’un réseau mondial de partenaires et de fournisseurs de services gérés (MSP : Managed Service Provider). Le siège de l’entreprise est basé à Oxford, au Royaume-Uni. Plus d’informations sont disponibles sur www.sophos.fr.