From the warning of gross force to a system of ransomware: thus an exposed RDP revealed a criminal operation

It takes very little for what looks like a routine alert to become the tip of an iceberg. A gross force warning against a Remoto Desktop (RDP) service exposed to the Internet is usually treated as a daily event: IP is blocked, attempts are reviewed and case closed. But when a response team decides to pull the thread with investigative curiosity, connections often appear that draw a much more sophisticated criminal operation.

In today's incident, a successful start-up after a brute force campaign opened the door to a forensic tour that revealed unusual behavior: an actor seeking credentials within files, an infrastructure distributed by countries and domains that referred to VPN-type services with promises of "no login." All of this fit into a Ransomware ecosystem as a service and the logic of those who sell initial access to networks to third parties.

RDP exposure remains one of the most used vectors. Although many organizations cannot help but offer remote access for operational reasons, this window to the outside world is a constant goal. Microsoft and cyber security specialists have been remembering the risks of publishing RDP services without appropriate protections for years; it is advisable to consult official guides to minimize the attack surface, such as Microsoft's technical documentation on remote access.

The forensic investigation started with Windows records: while in many environments the logs are overwritten with authentication attempts and lose value, in this case there were still useful traces. Analysts identified that, although multiple accounts were attacked, only one was compromised. What got the attention was that that account was used from several IP addresses, but with time patterns that indicated a single actor controlling different servers, not several independent attackers.

With access to the host, the attacker made a list of the domain and sought credentials. Here another anomaly emerged: instead of immediately resorting to automatic techniques for the extraction of credentials - such as the overturn of LSASS with known tools - the intruder opened text files with password-related names and visualized them with the Notebook. The jumplists confirmed the presence of manual searches within the system, a less common but effective procedure if there are secrets stored in files.

This behaviour led to a second phase of research: to track the associated PIs and TLS certificates. The cross-border of certificates and public data revealed domains and addresses that formed a network with a presence in multiple countries, often under the same name convention. This type of mapping is possible thanks to pivots on cryptographic prints and searches in public repositories such as Maltrail, who catalogued known malicious infrastructure.

From these pivots emerged suspicious domains and services that imitated legitimate VPN suppliers - with small differences in spelling - and others that explicitly offered "no records" policies, something very attractive to actors seeking anonymity. An operation-related domain was also linked to Ransomware families and reports from cybersecurity agencies. In particular, bodies such as the CISA have published notices that connect addresses and campaigns with groups of ransomware, which helps to confirm the seriousness of the finding.

The set of evidence - initial access by RDP, active file credentials searches, geographically replicated infrastructure and unscrupulous VPN services - fits what is known as a cybercrime value chain: initial access brokers selling access, and ransomware operators exploiting those access to encryption networks. To understand the techniques and procedures used by the attackers it is useful to refer to frames such as MITRE ATT & CK, which describe tactics such as the collection of credentials and the enumeration of domains.

Beyond the description of the attack, there are two clear operational lessons. The first is that defence teams earn a lot if they do not download "common" alerts and apply an inquisitive mentality: small data (a certificate, an IP, an open file) can become routes to map a complete adverse network. The second is that attackers do not always follow the manual: they sometimes adopt unorthodox methods, such as inspecting text files, which are counterintuitively fruitful and therefore must be considered in defensive playbooks.

In terms of mitigation, concrete and sustainable action should be taken. Avoid direct exposure of RDP to the public Internet, deploy multifactor authentication for remote access, and keep records of events with sufficient retention are basic pillars. It is also essential to monitor unusual connections and correlate them with search for certificates and domains associated with malicious infrastructure; for those who manage the defense, sources such as CISA StopRansomware offer up-to-date practical guides and resources.

Finally, the case underlines the importance of sharing intelligence and maintaining collaboration between response teams, security providers and agencies. When researchers were able to pivote from an IP to domains and services that imitated anonymity providers, that collective visibility made it possible to place the incident within a larger criminal economy, which is not achieved with a single, isolated record.

If anything is clear, the financial mechanisms of cybercrime are based on infrastructure and services that look like anodes: TLS certificates, small typosquating domains, and VPN offers "without records." Understanding how these elements are assembled and teaching teams to pull any suspicious thread is, today, one of the best ways to make life difficult for those who trade with access and extort organizations.

For those who want to deepen specific techniques and similar cases, in addition to the guides of government agencies, it is useful to consult technical repositories and forensic analysis published by specialized teams and response communities. A practical starting point for reviewing malicious infrastructure listings is the project Maltrail, and to explore examples of tools for the extraction of credentials you can see the repository of projects such as Mimikatz. There are also documentation and examples that independent researchers have collected in public gists that show how pivots of certificates and domains reveal whole networks.

In short, don't underestimate a brute force alert: with the right methodology and some research patience, it can become the key to discovering a network to support high-impact operations. And for those who defend systems, the recommendation does not change: priority is given to reducing exposure, proactive detection and collaboration between teams.