How a Brute Force Attack Exposed a Ransomware Network
â–¼ Summary
– A routine alert for a brute-force attack on an exposed RDP server revealed a successful compromise and unusual subsequent credential-hunting behavior within files, deviating from typical attacker playbooks.
– Investigators linked the attack IPs to known ransomware infrastructure, discovering a geo-distributed network of domains using a naming convention like NL-
– Further analysis of TLS certificates uncovered a suspicious VPN service domain (1vpns[.]com), which is similar to a legitimate service and is advertised as keeping no logs, making it ideal for cybercriminals.
– The evidence points to a ransomware-as-a-service ecosystem operated by initial access brokers, motivated to gather as many credentials as possible to facilitate attacks.
– This case demonstrates how investigating a common attack beyond initial containment can unravel a larger criminal infrastructure, providing rare insight into the actors’ operations and motivations.
For security teams, a brute force alert targeting an exposed Remote Desktop Protocol (RDP) server is often considered routine noise. Yet, a single, seemingly mundane alert recently provided a critical entry point into a sprawling ransomware-as-a-service (RaaS) ecosystem. By investigating a successful login, analysts uncovered a network of geo-distributed infrastructure and a suspicious VPN service, revealing the operational patterns of initial access brokers who sell network entry to ransomware gangs. This deep dive demonstrates how persistent investigation of common attacks can expose complex criminal operations.
The incident began when a security operations center (SOC) received an alert for domain enumeration. The affected network had an RDP server exposed to the internet, a common but high-risk practice often necessitated by business needs. Examining Windows event logs confirmed a brute force attack was in progress. While such attacks are fundamental, investigating them can be challenging; logs often overflow with failed attempts, burying critical data. In this instance, however, the necessary telemetry was preserved, showing that while many accounts were targeted, only one was successfully compromised.
This compromised account became a pivot point. Analysis revealed the account had been accessed from multiple IP addresses, an atypical pattern suggesting a single threat actor using distributed infrastructure rather than several independent attackers. After gaining access, the actor began enumerating the domain, examining groups and configurations. The SOC identified this activity as malicious and issued network-wide isolation to contain the threat, halting lateral movement.
At this stage, the incident appeared straightforward: a brute force success led to discovery and containment. However, a review of additional telemetry after isolation revealed unusual behavior that deviated from standard playbooks. Typically, intruders focus on extracting credentials from system processes like LSASS using tools such as Mimikatz or from the registry. This threat actor, however, manually searched through file systems and network shares, using Notepad to open text files suspected of containing passwords. This manual, file-centric approach to credential hunting is less common, as credentials in files can be outdated and require verification, unlike system-harvested credentials that are immediately useful.
This anomalous tradecraft prompted a re-examination of the IP addresses used in the brute force. Initial checks linked one IP to Hive ransomware, and other public reporting connected it to the BlackSuite ransomware group. Investigators then analyzed the TLS certificates associated with the attacking IP, uncovering a suspicious domain: `specialsseason[.]com`.
Pivoting from this domain’s TLS certificate fingerprint revealed a much larger infrastructure network. The team discovered numerous related IPs and domains following a naming convention like `NL-.specialsseason[.]com`. The list of country codes was extensive and geographically distributed, including multiple entries for Russia and the United States. The term “specials season” is known within cybercrime circles to refer to “big game hunting”, targeting high-value organizations for ransomware.
Further analysis of certificates from these IPs led to another malicious domain: `1vpns[.]com`. This domain closely mimics the legitimate `1vpn[.]org` service. Public threat reports have linked this VPN service to multiple ransomware groups. The service also advertised `1jabber[.]com` and `nologs[.]club`, the latter aligning with a “zero logs” policy attractive to cybercriminals seeking anonymity.
This investigation peeled back the curtain on the ransomware supply chain. It showed how initial access brokers operate, their motivation to gather vast amounts of credential material, and the infrastructure that supports them. The case underscores that defenders must sometimes look beyond immediate containment. What began as a simple brute force attack unraveled into the discovery of a professional RaaS infrastructure, providing rare behavioral insights that go beyond simple indicators of compromise.
Ransomware remains a pervasive threat, and while brute force is a basic technique, it should never be ignored. A deep, evidence-driven approach to investigation can transform a routine alert into intelligence that disrupts broader criminal operations. By pulling on every investigative thread, security teams can achieve a greater understanding of the adversary’s ecosystem, objectives, and methods.
(Source: Bleeping Computer)
