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March 4, 2019

The VR Goldilocks Problem and Value of Continued Recognition

Security and Operations Teams face challenges when it comes to visibility and recognition. Learn more about how we find a solution to the problems!
Inside the SOC
Darktrace cyber analysts are world-class experts in threat intelligence, threat hunting and incident response, and provide 24/7 SOC support to thousands of Darktrace customers around the globe. Inside the SOC is exclusively authored by these experts, providing analysis of cyber incidents and threat trends, based on real-world experience in the field.
Written by
Max Heinemeyer
Global Field CISO
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04
Mar 2019

First, some context about VR

Security Operations teams face two fundamental challenges when it comes to 'finding bad'.

The first is gaining and maintaining appropriate visibility into what is happening in our environments. Visibility is provided through data (e.g. telemetry, logs). The trinity of data sources for visibility concern accounts/credentials, devices, and network traffic.

The second challenge is getting good recognition within the scope of what is visible. Recognition is fundamentally about what alerting and workflows you can implement and automate in response to activity that is suspicious or malicious.

Visibility and Recognition each have their own different associated issues.

Visibility is a problem about what is and can be generated and either read as telemetry, or logged and stored locally, or shipped to a central platform. The timelines and completeness of what visibility you have can depend on factors such as how much data you can or can't store locally on devices that generate data - and for how long; what your data pipeline and data platform look like (e.g. if you are trying to centralise data for analysis); or the capability of host software agents you have to process certain information locally.

The constraints on visibility sets the bar for factors like coverage, timelines and completeness of what recognition you can achieve. Without visibility, we cannot recognize at all. With limited visibility, what we can recognize may not have much value. With the right visibility, we can still fail to recognise the right things. And with too much recognition, we can quickly overload our senses.

A good example of a technology that offers the opportunity to solve these challenges at the network layer is Darktrace. Their technology provides visibility, from a network traffic perspective, into data that concerns devices and the accounts/credentials associated with them. They then provide recognition on top of this by using Machine Learning (ML) models for anomaly detection. Their models alert on a wide range of activities that may be indicative of threat activity, (e.g. malware execution and command and control, a technical exploit, data exfiltration and so on).

The major advantage they provide, compared to traditional Intrusion Detection Systems (IDS) and other vendors who also use ML for network anomaly detection, is that you can a) adjust the sensitivity of their algorithms and b) build your own recognition for particular patterns of interest. For example, if you want to monitor what connections are made to one or two servers, you can set up alerts for any change to expected patterns. This means you can create and adjust custom recognition based on your enterprise context and tune it easily in response to how context changes over time.

The Goldilocks VR Matrix

Below is what we call the VR Goldilocks Matrix at PBX Group Security. We use it to assess technology, measure our own capability and processes, and ask ourselves hard questions about where we need to focus to get the most value from our budget, (or make cuts / shift investment) if we need to.

In the squares are some examples of what you (maybe) should think about doing if you find yourself there.

Important questions to ask about VR

One of the things about Visibility and Recognition is that it’s not a given they are ‘always on’. Sometimes there are failure modes for visibility (causing a downstream issue with recognition). And sometimes there are failure modes or conditions under which you WANT to pause recognition.

The key questions you must have answers to about this include:

  • Under what conditions might I lose visibility?
  • How would I know if I have?
  • Is that loss a blind spot (i.e. data is lost for a given time period)…
  • …or is it 'a temporal delay’ (e.g. a connection fails and data is batched for moving from A to B but that doesn’t happen for a few hours)?
  • What are the recognitions that might be impacted by either of the above?
  • What is my expectation for the SLA on those recognitions from ‘cause of alert’ to ‘response workflow’?
  • Under what conditions would I be willing to pause recognition, change the workflow for what happens upon recognition, or stop it all together?
  • What is the stacked ranked list of ‘must, should, could’ for all recognition and why?

Alerts. Alerts everywhere.

More often than not, Security Operations teams suffer the costs of wasted time due to noisy alerts from certain data sources. As a consequence, it's more difficult for them to single out malicious behavior as suspicious or benign. The number of alerts that are generated due to out of the box SIEM platform configurations for sources like Web Proxies and Domain Controllers are often excessive, and the cost to tune those rules can also be unpalatable. Therefore, rather than trying to tune alerts, teams might make a call to switch them off until someone can get around to figuring out a better way. There’s no use having hypothetical recognition, but no workflow to act on what is generate (other than compliance).

This is where technologies that use ML can help. There are two basic approaches...

One is to avoid alerting until multiple conditions are met that indicate a high probability of threat activity. In this scenario, rather than alerting on the 1st, 2nd, 3rd and 4th ‘suspicious activities’, you wait until you have a critical mass of indicators, and then you generate one high fidelity alert that has a much greater weighting to be malicious. This requires both a high level of precision and accuracy in alerting, and naturally some trade off in the time that can pass before an alert for malicious activity is generated.

The other is to alert on ‘suspicious actives 1-4' and let an analyst or automated process decide if this merits further investigation. This approach sacrifices accuracy for precision, but provides rapid context on whether one, or multiple, conditions are met that push the machine(s) up the priority list in the triage queue. To solve for the lower level of accuracy, this approach can make decisions about how long to sustain alerting. For example, if a host triggers multiple anomaly detection models, rather than continue to send alerts (and risk the SOC deciding to turn them off), the technology can pause alerts after a certain threshold. If a machine has not been quarantined or taken off the network after 10 highly suspicious behaviors are flagged, there is a reasonable assumption that the analyst will have dug into these and found the activity is legitimate.

Punchline 1: the value of Continued Recognition even when 'not malicious'

The topic of paused detections was raised after a recent joint exercise between PBX Group Security and Darktrace in testing Darktrace’s recognition. After a machine being used by the PBX Red Team breached multiple high priority models on Darktrace, the technology stopped alerting on further activity. This was because the initial alerts would have been severe enough to trigger a SOC workflow. This approach is designed to solve the problem of alert overload on a machine that is behaving anomalously but is not in fact malicious. Rather than having the SOC turn off alerts for that machine (which could later be used maliciously), the alerts are paused.

One of the outcomes of the test was that the PBX Detect team advised they would still want those alerts to exist for context to see what else the machine does (i.e. to understand its pattern of life). Now, rather than pausing alerts, Darktrace is surfacing this to customers to show where a rule is being paused and create an option to continue seeing alerts for a machine that has breached multiple models.

Which leads us on to our next point…

Punchline 2: the need for Atomic Tests for detection

Both Darktrace and Photobox Security are big believers in Atomic Red Team testing, which involves ‘unit tests’ that repeatedly (or at a certain frequency) test a detection using code. Unit tests automate the work of Red Teams when they discovery control strengths (which you want to monitor continuously for uptime) or control gaps (which you want to monitor for when they are closed). You could design atomic tests to launch a series of particular attacks / threat actor actions from one machine in a chained event. Or you could launch different discreet actions from different machines, each of which has no prior context for doing bad stuff. This allows you to scale the sample size for testing what recognition you have (either through ML or more traditional SIEM alerting). Doing this also means you don't have to ask Red Teams to repeat the same tests again, allowing them to focus on different threat paths to achieve objectives.

Mitre Att&ck is an invaluable framework for this. Many vendors are now aligning to Att&ck to show what they can recognize relating to attack TTPs (Tools, Tactics and Procedures). This enables security teams to map what TTPs are relevant to them (e.g. by using threat intel about the campaigns of threat actor groups that are targeting them). Atomic Red Team tests can then be used to assure that expected detections are operational or find gaps that need closing.

If you miss detections, then you know you need to optimise the recognition you have. If you get too many recognitions outside of the atomic test conditions, you either have to accept a high false positive rate because of the nature of the network, or you can tune your detection sensitivity. The opportunities to do this with technology based on ML and anomaly detection are significant, because you can quickly see for new attack types what a unit test tells you about your current detections and that coverage you think you have is 'as expected'.

Punchline 3: collaboration for the win

Using well-structured Red Team exercises can help your organisation and your technology partners learn new things about how we can collectively find and halt evil. They can also help defenders learn more about good assumptions to build into ML models, as well as covering edge cases where alerts have 'business intelligence' value vs ‘finding bad’.

If you want to understand the categorisations of ways that your populations of machines act over time, there is no better way to do it than through anomaly detection and feeding alerts into a system that supports SOC operations as well as knowledge management (e.g. a graph database).

Working like this means that we also help get the most out of the visibility and recognition we have. Security solutions can be of huge help to Network and Operations teams for troubleshooting or answering questions about network architecture. Often, it’s just a shift in perspective that unlocks cross-functional value from investments in security tech and process. Understanding that recognition doesn’t stop with security is another great example of where technologies that let you build your own logic into recognition can make a huge difference above protecting the bottom line, to adding top line value.

Inside the SOC
Darktrace cyber analysts are world-class experts in threat intelligence, threat hunting and incident response, and provide 24/7 SOC support to thousands of Darktrace customers around the globe. Inside the SOC is exclusively authored by these experts, providing analysis of cyber incidents and threat trends, based on real-world experience in the field.
Written by
Max Heinemeyer
Global Field CISO

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November 27, 2025

CastleLoader & CastleRAT: Behind TAG150’s Modular Malware Delivery System

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What is TAG-150?

TAG-150, a relatively new Malware-as-a-Service (MaaS) operator, has been active since March 2025, demonstrating rapid development and an expansive, evolving infrastructure designed to support its malicious operations. The group employs two custom malware families, CastleLoader and CastleRAT, to compromise target systems, with a primary focus on the United States [1]. TAG-150’s infrastructure included numerous victim-facing components, such as IP addresses and domains functioning as command-and-control (C2) servers associated with malware families like SecTopRAT and WarmCookie, in addition to CastleLoader and CastleRAT [2].

As of May 2025, CastleLoader alone had infected a reported 469 devices, underscoring the scale and sophistication of TAG-150’s campaign [1].

What are CastleLoader and CastleRAT?

CastleLoader is a loader malware, primarily designed to download and install additional malware, enabling chain infections across compromised systems [3]. TAG-150 employs a technique known as ClickFix, which uses deceptive domains that mimic document verification systems or browser update notifications to trick victims into executing malicious scripts. Furthermore, CastleLoader leverages fake GitHub repositories that impersonate legitimate tools as a distribution method, luring unsuspecting users into downloading and installing malware on their devices [4].

CastleRAT, meanwhile, is a remote access trojan (RAT) that serves as one of the primary payloads delivered by CastleLoader. Once deployed, CastleRAT grants attackers extensive control over the compromised system, enabling capabilities such as keylogging, screen capturing, and remote shell access.

TAG-150 leverages CastleLoader as its initial delivery mechanism, with CastleRAT acting as the main payload. This two-stage attack strategy enhances the resilience and effectiveness of their operations by separating the initial infection vector from the final payload deployment.

How are they deployed?

Castleloader uses code-obfuscation methods such as dead-code insertion and packing to hinder both static and dynamic analysis. After the payload is unpacked, it connects to its command-and-control server to retrieve and running additional, targeted components.

Its modular architecture enables it to function both as a delivery mechanism and a staging utility, allowing threat actors to decouple the initial infection from payload deployment. CastleLoader typically delivers its payloads as Portable Executables (PEs) containing embedded shellcode. This shellcode activates the loader’s core module, which then connects to the C2 server to retrieve and execute the next-stage malware.[6]

Following this, attackers deploy the ClickFix technique, impersonating legitimate software distribution platforms like Google Meet or browser update notifications. These deceptive sites trick victims into copying and executing PowerShell commands, thereby initiating the infection kill chain. [1]

When a user clicks on a spoofed Cloudflare “Verification Stepprompt, a background request is sent to a PHP script on the distribution domain (e.g., /s.php?an=0). The server’s response is then automatically copied to the user’s clipboard using the ‘unsecuredCopyToClipboard()’ function. [7].

The Python-based variant of CastleRAT, known as “PyNightShade,” has been engineered with stealth in mind, showing minimal detection across antivirus platforms [2]. As illustrated in Figure 1, PyNightShade communicates with the geolocation API service ip-api[.]com, demonstrating both request and response behavior

Packet Capture (PCAP) of PyNightShade, the Python-based variant of CastleRAT, communicating with the geolocation API service ip-api[.]com.
Figure 1: Packet Capture (PCAP) of PyNightShade, the Python-based variant of CastleRAT, communicating with the geolocation API service ip-api[.]com.

Darktrace Coverage

In mid-2025, Darktrace observed a range of anomalous activities across its customer base that appeared linked to CastleLoader, including the example below from a US based organization.

The activity began on June 26, when a device on the customer’s network was observed connecting to the IP address 173.44.141[.]89, a previously unseen IP for this network along with the use of multiple user agents, which was also rare for the user.  It was later determined that the IP address was a known indicator of compromise (IoC) associated with TAG-150’s CastleRAT and CastleLoader operations [2][5].

Figure 2: Darktrace’s detection of a device making unusual connections to the malicious endpoint 173.44.141[.]89.

The device was observed downloading two scripts from this endpoint, namely ‘/service/download/data_5x.bin’ and ‘/service/download/data_6x.bin’, which have both been linked to CastleLoader infections by open-source intelligence (OSINT) [8]. The archives contains embedded shellcode, which enables attackers to execute arbitrary code directly in memory, bypassing disk writes and making detection by endpoint detection and response (EDR) tools significantly more difficult [2].

 Darktrace’s detection of two scripts from the malicious endpoint.
Figure 3: Darktrace’s detection of two scripts from the malicious endpoint.

In addition to this, the affected device exhibited a high volume of internal connections to a broad range of endpoints, indicating potential scanning activity. Such behavior is often associated with reconnaissance efforts aimed at mapping internal infrastructure.

Darktrace / NETWORK correlated these behaviors and generated an Enhanced Monitoring model, a high-fidelity security model designed to detect activity consistent with the early stages of an attack. These high-priority models are continuously monitored and triaged by Darktrace’s Security Operations Center (SOC) as part of the Managed Threat Detection and Managed Detection & Response services, ensuring that subscribed customers are promptly alerted to emerging threats.

Darktrace detected an unusual ZIP file download alongside the anomalous script, followed by internal connectivity. This activity was correlated under an Enhanced Monitoring model.
Figure 4: Darktrace detected an unusual ZIP file download alongside the anomalous script, followed by internal connectivity. This activity was correlated under an Enhanced Monitoring model.

Darktrace Autonomous Response

Fortunately, Darktrace’s Autonomous Response capability was fully configured, enabling it to take immediate action against the offending device by blocking any further connections external to the malicious endpoint, 173.44.141[.]89. Additionally, Darktrace enforced a ‘group pattern of life’ on the device, restricting its behavior to match other devices in its peer group, ensuring it could not deviate from expected activity, while also blocking connections over 443, shutting down any unwanted internal scanning.

Figure 5: Actions performed by Darktrace’s Autonomous Response to contain the ongoing attack.

Conclusion

The rise of the MaaS ecosystem, coupled with attackers’ growing ability to customize tools and techniques for specific targets, is making intrusion prevention increasingly challenging for security teams. Many threat actors now leverage modular toolkits, dynamic infrastructure, and tailored payloads to evade static defenses and exploit even minor visibility gaps. In this instance, Darktrace demonstrated its capability to counter these evolving tactics by identifying early-stage attack chain behaviors such as network scanning and the initial infection attempt. Autonomous Response then blocked the CastleLoader IP delivering the malicious ZIP payload, halting the attack before escalation and protecting the organization from a potentially damaging multi-stage compromise

Credit to Ahmed Gardezi (Cyber Analyst) Tyler Rhea (Senior Cyber Analyst)
Edited by Ryan Traill (Analyst Content Lead)

Appendices

Darktrace Model Detections

  • Anomalous Connection / Unusual Internal Connections
  • Anomalous File / Zip or Gzip from Rare External Location
  • Anomalous File / Script from Rare External Location
  • Initial Attack Chain Activity (Enhanced Monitoring Model)

MITRE ATT&CK Mapping

  • T15588.001 - Resource Development – Malware
  • TG1599 – Defence Evasion – Network Boundary Bridging
  • T1046 – Discovery – Network Service Scanning
  • T1189 – Initial Access

List of IoCs
IoC - Type - Description + Confidence

  • 173.44.141[.]89 – IP – CastleLoader C2 Infrastructure
  • 173.44.141[.]89/service/download/data_5x.bin – URI – CastleLoader Script
  • 173.44.141[.]89/service/download/data_6x.bin – URI  - CastleLoader Script
  • wsc.zip – ZIP file – Possible Payload

References

[1] - https://blog.polyswarm.io/castleloader

[2] - https://www.recordedfuture.com/research/from-castleloader-to-castlerat-tag-150-advances-operations

[3] - https://www.pcrisk.com/removal-guides/34160-castleloader-malware

[4] - https://www.scworld.com/brief/malware-loader-castleloader-targets-devices-via-fake-github-clickfix-phishing

[5] https://www.virustotal.com/gui/ip-address/173.44.141.89/community

[6] https://thehackernews.com/2025/07/castleloader-malware-infects-469.html

[7] https://www.cryptika.com/new-castleloader-attack-using-cloudflare-themed-clickfix-technique-to-infect-windows-computers/

[8] https://www.cryptika.com/castlebot-malware-as-a-service-deploys-range-of-payloads-linked-to-ransomware-attacks/

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Ahmed Gardezi
Cyber Analyst

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November 26, 2025

UK Cyber Security & Resilience Bill: What Organizations Need to Know

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Why the Bill has been introduced

The UK’s cyber threat landscape has evolved dramatically since the 2018 NIS regime was introduced. Incidents such as the Synnovis attack against hospitals and the British Library ransomware attack show how quickly operational risk can become public harm. In this context, the UK Department for Science, Innovation and Technology estimates that cyber-attacks cost UK businesses around £14.7 billion each year.

At the same time, the widespread adoption of AI has expanded organisations’ attack surfaces and empowered threat actors to launch more effective and sophisticated activities, including crafting convincing phishing campaigns, exploiting vulnerabilities and initiating ransomware attacks at unprecedented speed and scale.  

The CSRB responds to these challenges by widening who is regulated, accelerating incident reporting and tightening supply chain accountability, while enabling rapid updates that keep pace with technology and emerging risks.

Key provisions of the Cyber Security and Resilience Bill

A wider set of organisations in scope

The Bill significantly broadens the range of organisations regulated under the NIS framework.

  • Managed service providers (MSPs) - medium and large MSPs, including MSSPs, managed SOCs, SIEM providers and similar services,will now fall under NIS obligations due to their systemic importance and privileged access to client systems. The Information Commissioner’s Office (ICO) will act as the regulator. Government analysis anticipates that a further 900 to 1,100 MSPs will be in scope.
  • Data infrastructure is now recognised as essential to the functioning of the economy and public services. Medium and large data centres, as well as enterprise facilities meeting specified thresholds, will be required to implement appropriate and proportionate measures to manage cyber risk. Oversight will be shared between DSIT and Ofcom, with Ofcom serving as the operational regulator.
  • Organisations that manage electrical loads for smart appliances, such as those supporting EV charging during peak times, are now within scope.

These additions sit alongside existing NIS-regulated sectors such as transport, energy, water, health, digital infrastructure, and certain digital services (including online marketplaces, search engines, and cloud computing).

Stronger supply chain requirements

Under the CSRB, regulators can now designate third-party suppliers as ‘designated critical suppliers’ (DCS) when certain threshold criteria are met and where disruption could have significant knock-on effects. Designated suppliers will be subject to the same security and incident-reporting obligations as Operators of Essential Services (OES) and Relevant Digital Service Providers (RDSPs).

Government will scope the supply chain duties for OES and RDSPs via secondary legislation, following consultation. infrastructure incidents where a single supplier’s compromise caused widespread disruption.

Faster incident reporting

Sector-specific regulators, 12 in total, will be responsible for implementing the CSRB, allowing for more effective and consistent reporting. In addition, the CSRB introduces a two-stage reporting process and expands incident reporting criteria. Regulated entities must submit an initial notification within 24 hours of becoming aware of a significant incident, followed by an incident report within 72 hours. Incident reporting criteria are also broadened to capture incidents beyond those which actually resulted in an interruption, ensuring earlier visibility for regulators and the National Cyber Security Centre (NCSC). The importance of information sharing across agencies, law enforcement and regulators is also facilitated by the CSRB.

The reforms also require data centres and managed service providers to notify affected customers where they are likely to have been impacted by a cyber incident.

An agile regulatory framework

To keep pace with technological change, the CSRB will enable the Secretary of State to update elements of the framework via secondary legislation. Supporting materials such as the NCSC Cyber Assessment Framework (CAF) are to be "put on a stronger footing” allowing for requirements to be more easily followed, managed and updated. Regulators will also now be able to recover full costs associated with NIS duties meaning they are better resourced to carry out their associated responsibilities.

Relevant Managed Service Providers must identify and take appropriate and proportionate measures to manage risks to the systems they rely on for providing services within the UK. Importantly, these measures must, having regard to the state of the art, ensure a level of security appropriate to the risk posed, and prevent or minimise the impact of incidents.

The Secretary of State will also be empowered to issue a Statement of Strategic Priorities, setting cross-regime outcomes to drive consistency across the 12 competent authorities responsible for implementation.

Penalties

The enforcement framework will be strengthened, with maximum fines aligned with comparable regimes such as the GDPR, which incorporate maximums tied to turnover. Under the CSRB, maximum penalties for more serious breaches could be up to £17 million or 4% of global turnover, whichever is higher.

Next steps

The Bill is expected to progress through Parliament over the course of 2025 and early 2026, with Royal Assent anticipated in 2026. Once enacted, most operational measures will not take immediate effect. Instead, Government will bring key components into force through secondary legislation following further consultation, providing regulators and industry with time to adjust practices and prepare for compliance.

Anticipated timeline

  • 2025-2026: Parliamentary scrutiny and passage;
  • 2026: Royal Assent;  
  • 2026 consultation: DSIT intends to consult on detailed implementation;
  • From 2026 onwards: Phased implementation via secondary legislation, following further consultation led by DSIT.

How Darktrace can help

The CSRB represents a step change in how the UK approaches digital risk, shifting the focus from compliance to resilience.

Darktrace can help organisations operationalise this shift by using AI to detect, investigate and respond to emerging threats at machine speed, before they escalate into incidents requiring regulatory notification. Proactive tools which can be included in the Darktrace platform allow security teams to stress-test defences, map supply chain exposure and rehearse recovery scenarios, directly supporting the CSRB’s focus on resilience, transparency and rapid response. If an incident does occur, Darktrace’s autonomous agent, Cyber AI Analyst, can accelerate investigations and provide a view of every stage of the attack chain, supporting timely reporting.  

Darktrace’s AI can provide organisations with a vital lens into both internal and external cyber risk. By continuously learning patterns of behaviour across interconnected systems, Darktrace can flag potential compromise or disruption to detect supply chain risk before it impacts your organisation.

In a landscape where compliance and resilience go hand in hand, Darktrace can equip organisations to stay ahead of both evolving threats and evolving regulatory requirements.

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