Darktrace Detects Malicious ISO Files with AI Darktrace Email
Darktrace AI detects malicious ISO file in email attack. Learn more about how Antigena Email stopped the attack without relying on signatures or blacklists.
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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.
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26
Aug 2020
Darktrace has recently seen a string of email attacks that use some degree of social engineering to convince the recipient to open a misleading link and divulge their credentials. In this blog, we look at an email attack targeting a Spanish customer that involved hiding malicious content in an unusual file type that is not regularly checked by common email security tools.
An ISO file, often referred to as an ISO image, is an archive file that contains an identical copy of data found on an optical disc, like a CD or DVD. They are primarily used for backing up optical discs or distributing large file sets that are intended to be burned onto an optical disc. Since they are relatively unusual – and are typically extremely large files – most standard email controls don’t analyze them in any depth, if at all.
Darktrace detected one cyber-criminal using ISO files to inflict damage on a food distributor in Spain. The organization, which had adopted Antigena Email just two weeks earlier, received around 84 emails from the same sender, each containing a malicious ISO attachment. The emails were received from info@valeplaz[.]com, a clever and well-executed spoof of the email address info@valenplas[.]com, which is the contact email of a legitimate Spanish manufacturer – possibly even a supplier of the victim organization.
Figure 1: A snapshot of Antigena Email’s user interface
Darktrace noticed that the sender had never been seen in any prior correspondences across the business. Additionally, the personal field does not correspond with the header in the email itself – which is what would be visible to the recipient. In the connection IP address and checks, Darktrace’s AI revealed that the true sender does not correspond with the domain valeplaz[.]com.
The subject line suggests that the email is about an order the client made. Analyzing the attachments, Darktrace surfaced a file titled URGENTE_PO_120620.iso. The name of the file suggests the sender is attempting to use the social engineering tactic of urgency in order to alarm the recipients, leading them to jump into action and click a link or open attachments without carefully considering the details of the email.
Darktrace’s AI also recognized that the file extension .iso is highly anomalous for the group, user, and the organization as a whole. Even more suspiciously, the size of the attachment is incredibly small (just 485.4 kB), which makes it highly unlikely that it was, in fact, a genuine invoice in the form of a PDF or Word attachment. These findings, in conjunction with the New Contact and Wide Distribution tags of the email, caused Antigena Email to strip the email of the attachment and hold it back from each recipient’s inbox. In addition, Darktrace’s AI revealed that the email contained an anomalous link which it deemed highly suspicious, and locked the link in all emails while the security team investigated the incident.
Figure 2: The suspicious link in question
Stopping the attack without a Patient Zero
When the security team later checked the file hash on the attachment, they discovered that some anti-virus vendors, including Microsoft, had already labelled it as malware. The crucial challenge is to stop the malicious email in the first instance – before it lands in the first inbox. With a continuously updated understanding of ‘self’, Darktrace’s AI is able to do just that – stopping attacks without requiring a ‘Patient Zero’ be infected.
Moreover, many legacy solutions hadn’t yet recognized this file hash as malicious, suggesting that this was a relatively new attack. This exposes an increasingly obvious limitation of such tools – attackers are refreshing their attack infrastructure so often that no matter how frequently legacy tools or blacklists are updated, they are outdated almost immediately.
Antigena Email caught this attack without relying on any signatures and blacklists, but instead by learning whether or not the email, file, and behavior was normal for the unique business. With Cyber AI protecting their inbox, this organization was able to thwart this attack in the first instance – before any emails landed in an inbox or any employees clicked on the link.
No items found.
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.
WSUS Exploited: Darktrace’s Analysis of Post-Exploitation Activities Related to CVE-2025-59287
Introduction
On October 14, 2025, Microsoft disclosed a new critical vulnerability affecting the Windows Server Update Service (WSUS), CVE-2025-59287. Exploitation of the vulnerability could allow an unauthenticated attacker to remotely execute code [1][6].
WSUS allows for centralized distribution of Microsoft product updates [3]; a server running WSUS is likely to have significant privileges within a network making it a valuable target for threat actors. While WSUS servers are not necessarily expected to be open to the internet, open-source intelligence (OSINT) has reported thousands of publicly exposed instances that may be vulnerable to exploitation [2].
Microsoft’s initial ‘Patch Tuesday’ update for this vulnerability did not fully mitigate the risk, and so an out-of-band update followed on October 23 [4][5] . Widespread exploitation of this vulnerability started to be observed shortly after the security update [6], prompting CISA to add CVE-2025-59287 to its Known Exploited Vulnerability Catalog (KEV) on October 24 [7].
Attack Overview
The Darktrace Threat Research team have recently identified multiple potential cases of CVE-2025-59287 exploitation, with two detailed here. While the likely initial access method is consistent across the cases, the follow-up activities differed, demonstrating the variety in which such a CVE can be exploited to fulfil each attacker’s specific goals.
The first signs of suspicious activity across both customers were detected by Darktrace on October 24, the same day this vulnerability was added to CISA’s KEV. Both cases discussed here involve customers based in the United States.
Case Study 1
The first case, involving a customer in the Information and Communication sector, began with an internet-facing device making an outbound connection to the hostname webhook[.]site. Observed network traffic indicates the device was a WSUS server.
OSINT has reported abuse of the workers[.]dev service in exploitation of CVE-2025-59287, where enumerated network information gathered through running a script on the compromised device was exfiltrated using this service [8].
In this case, the majority of connectivity seen to webhook[.]site involved a PowerShell user agent; however, cURL user agents were also seen with some connections taking the form of HTTP POSTs. This connectivity appears to align closely with OSINT reports of CVE-2025-59287 post-exploitation behaviour [8][9].
Connections to webhook[.]site continued until October 26. A single URI was seen consistently until October 25, after which the connections used a second URI with a similar format.
Later on October 26, an escalation in command-and-control (C2) communication appears to have occurred, with the device starting to make repeated connections to two rare workers[.]dev subdomains (royal-boat-bf05.qgtxtebl.workers[.]dev & chat.hcqhajfv.workers[.]dev), consistent with C2 beaconing. While workers[.]dev is associated with the legitimate Cloudflare Workers service, the service is commonly abused by malicious actors for C2 infrastructure. The anomalous nature of the connections to both webhook[.]site and workers[.]dev led to Darktrace generating multiple alerts including high-fidelity Enhanced Monitoring alerts and alerts for Darktrace’s Autonomous Response.
Infrastructure insight
Hosted on royal-boat-bf05.qgtxtebl.workers[.]dev is a Microsoft Installer file (MSI) named v3.msi.
Figure 1: Screenshot of v3.msi content.
Contained in the MSI file is two Cabinet files named “Sample.cab” and “part2.cab”. After extracting the contents of the cab files, a file named “Config” and a binary named “ServiceEXE”. ServiceEXE is the legitimate DFIR tool Velociraptor, and “Config” contains the configuration details, which include chat.hcqhajfv.workers[.]dev as the server_url, suggesting that Velociraptor is being used as a tunnel to the C2. Additionally, the configuration points to version 0.73.4, a version of Velociraptor that is vulnerable to CVE-2025-6264, a privilege escalation vulnerability.
Figure 2: Screenshot of Config file.
Velociraptor, a legitimate security tool maintained by Rapid7, has been used recently in malicious campaigns. A vulnerable version of tool has been used by threat actors for command execution and endpoint takeover, while other campaigns have used Velociraptor to create a tunnel to the C2, similar to what was observed in this case [10] .
The workers[.]dev communication continued into the early hours of October 27. The most recent suspicious behavior observed on the device involved an outbound connection to a new IP for the network - 185.69.24[.]18/singapure - potentially indicating payload retrieval.
The payload retrieved from “/singapure” is a UPX packed Windows binary. After unpacking the binary, it is an open-source Golang stealer named “Skuld Stealer”. Skuld Stealer has the capabilities to steal crypto wallets, files, system information, browser data and tokens. Additionally, it contains anti-debugging and anti-VM logic, along with a UAC bypass [11].
Figure 3: A timeline outlining suspicious activity on the device alerted by Darktrace.
Case Study 2
The second case involved a customer within the Education sector. The affected device was also internet-facing, with network traffic indicating it was a WSUS server
Suspicious activity in this case once again began on October 24, notably only a few seconds after initial signs of compromise were observed in the first case. Initial anomalous behaviour also closely aligned, with outbound PowerShell connections to webhook[.]site, and then later connections, including HTTP POSTs, to the same endpoint with a cURL user agent.
While Darktrace did not observe any anomalous network activity on the device after October 24, the customer’s security integration resulted in an additional alert on October 27 for malicious activity, suggesting that the compromise may have continued locally.
By leveraging Darktrace’s security integrations, customers can investigate activity across different sources in a seamless manner, gaining additional insight and context to an attack.
Figure 4: A timeline outlining suspicious activity on the device alerted by Darktrace.
Conclusion
Exploitation of a CVE can lead to a wide range of outcomes. In some cases, it may be limited to just a single device with a focused objective, such as exfiltration of sensitive data. In others, it could lead to lateral movement and a full network compromise, including ransomware deployment. As the threat of internet-facing exploitation continues to grow, security teams must be prepared to defend against such a possibility, regardless of the attack type or scale.
By focussing on detection of anomalous behaviour rather than relying on signatures associated with a specific CVE exploit, Darktrace is able to alert on post-exploitation activity regardless of the kind of behaviour seen. In addition, leveraging security integrations provides further context on activities beyond the visibility of Darktrace / NETWORK, enabling defenders to investigate and respond to attacks more effectively.
With adversaries weaponizing even trusted incident response tools, maintaining broad visibility and rapid response capabilities becomes critical to mitigating post-exploitation risk.
Credit to Emma Foulger (Global Threat Research Operations Lead), Tara Gould (Threat Research Lead), Eugene Chua (Principal Cyber Analyst & Analyst Team Lead), Nathaniel Jones (VP, Security & AI Strategy, Field CISO),
o royal-boat-bf05.qgtxtebl.workers[.]dev – Hostname – Likely C2 Infrastructure
o royal-boat-bf05.qgtxtebl.workers[.]dev/v3.msi - URI – Likely payload
o chat.hcqhajfv.workers[.]dev – Hostname – Possible C2 Infrastructure
o 185.69.24[.]18 – IP address – Possible C2 Infrastructure
o 185.69.24[.]18/bin.msi - URI – Likely payload
o 185.69.24[.]18/singapure - URI – Likely payload
The content provided in this blog is published by Darktrace for general informational purposes only and reflects our understanding of cybersecurity topics, trends, incidents, and developments at the time of publication. While we strive to ensure accuracy and relevance, the information is provided “as is” without any representations or warranties, express or implied. Darktrace makes no guarantees regarding the completeness, accuracy, reliability, or timeliness of any information presented and expressly disclaims all warranties.
Nothing in this blog constitutes legal, technical, or professional advice, and readers should consult qualified professionals before acting on any information contained herein. Any references to third-party organizations, technologies, threat actors, or incidents are for informational purposes only and do not imply affiliation, endorsement, or recommendation.
Darktrace, its affiliates, employees, or agents shall not be held liable for any loss, damage, or harm arising from the use of or reliance on the information in this blog.
The cybersecurity landscape evolves rapidly, and blog content may become outdated or superseded. We reserve the right to update, modify, or remove any content
Patch Smarter, Not Harder: Now Empowering Security Teams with Business-Aligned Threat Context Agents
Most risk management programs remain anchored in enumeration: scanning every asset, cataloging every CVE, and drowning in lists that rarely translate into action. Despite expensive scanners, annual pen tests, and countless spreadsheets, prioritization still falters at two critical points.
Context gaps at the device level: It’s hard to know which vulnerabilities actually matter to your business given existing privileges, what software it runs, and what controls already reduce risk.
Business translation: Even when the technical priority is clear, justifying effort and spend in financial terms—especially across many affected devices—can delay action. Especially if it means halting other areas of the business that directly generate revenue.
The result is familiar: alert fatigue, “too many highs,” and remediation that trails behind the threat landscape. Darktrace / Proactive Exposure Management addresses this by pairing precise, endpoint‑level context with clear, financial insight so teams can prioritize confidently and mobilize faster.
A powerful combination: No-Telemetry Endpoint Agent + Cost-Benefit Analysis
Darktrace / Proactive Exposure Management now uniquely combines technical precision with business clarity in a single workflow. With this release, Darktrace / Proactive Exposure Management delivers a more holistic approach, uniting technical context and financial insight to drive proactive risk reduction. The result is a single solution that helps security teams stay ahead of threats while reducing noise, delays, and complexity.
No-Telemetry Endpoint: Collects installed software data and maps it to known CVEs—without network traffic—providing device-level vulnerability context and operational relevance.
Cost-Benefit Analysis for Patching: Calculates ROI by comparing patching effort with potential exploit impact, factoring in headcount time, device count, patch difficulty, and automation availability.
Introducing the No-Telemetry Endpoint Agent
Darktrace’s new endpoint agent inventories installed software on devices and maps it to known CVEs without collecting network data so you can prioritize using real device context and available security controls.
By grounding vulnerability findings in the reality of each endpoint, including its software footprint and existing controls, teams can cut through generic severity scores and focus on what matters most. The agent is ideal for remote devices, BYOD-adjacent fleets, or environments standardizing on Darktrace, and is available without additional licensing cost.
Figure 1: Darktrace / Proactive Exposure Management user interface
Built-In Cost-Benefit Analysis for Patching
Security teams often know what needs fixing but stakeholders need to understand why now. Darktrace’s new cost-benefit calculator compares the total cost to patch against the potential cost of exploit, producing an ROI for the patch action that expresses security action in clear financial terms.
Inputs like engineer time, number of affected devices, patch difficulty, and automation availability are factored in automatically. The result is a business-aligned justification for every patching decision—helping teams secure buy-in, accelerate approvals, and move work forward with one-click ticketing, CSV export, or risk acceptance.
Together, the no-telemetry endpoint and Cost–Benefit Analysis advance the CTEM motion from theory to practice. You gain higher‑fidelity discovery and validation signals at the device level, paired with business‑ready justification that accelerates mobilization. The result is fewer distractions, clearer priorities, and faster measurable risk reduction. This is not from chasing every alert, but by focusing on what moves the needle now.
Smarter Prioritization: Device‑level context trims noise and spotlights the exposures that matter for your business.
Faster Decisions: Built‑in ROI turns technical urgency into executive clarity—speeding approvals and action.
Practical Execution: Privacy‑conscious endpoint collection and ticketing/export options fit neatly into existing workflows.
Better Outcomes: Close the loop faster—discover, prioritize, validate, and mobilize—on the same operating surface.
Committed to innovation
These updates are part of the broader Darktrace release, which also included:
3. Improvements to our OT product, purpose built for industrial infrastructure, Darktrace / OT now brings dedicated OT dashboard, segmentation-aware risk modeling, and expanded visibility into edge assets and automation protocols.
Join our live broadcast to experience how Darktrace is eliminating blind spots for detection and response across your complete enterprise with new innovations in Agentic AI across our ActiveAI Security platform. Industry leaders from IDC will join Darktrace customers to discuss challenges in cross-domain security, with a live walkthrough reshaping the future of Network Detection & Response, Endpoint Detection & Response, Email Security, and SecOps in novel threat detection and autonomous investigations.
