{ "id": "e4317114-0ea9-4998-bd60-dd44153fb5cd", "created_at": "2026-04-06T00:12:33.418721Z", "updated_at": "2026-04-10T13:11:41.938698Z", "deleted_at": null, "sha1_hash": "ee03eda84b004bb6ca0a939346c98310fe77067f", "title": "Suspected AsyncRAT Delivered via ISO Files Using HTML Smuggling Technique", "llm_title": "", "authors": "", "file_creation_date": "0001-01-01T00:00:00Z", "file_modification_date": "0001-01-01T00:00:00Z", "file_size": 84301, "plain_text": "Suspected AsyncRAT Delivered via ISO Files Using HTML\r\nSmuggling Technique\r\nBy eSentire Threat Response Unit (TRU)\r\nArchived: 2026-04-05 19:27:06 UTC\r\nAdversaries don’t work 9-5 and neither do we. At eSentire, our 24/7 SOCs are staffed with Elite Threat Hunters\r\nand Cyber Analysts who hunt, investigate, contain and respond to threats within minutes.\r\nWe have discovered some of the most dangerous threats and nation state attacks in our space – including the\r\nKaseya MSP breach and the more_eggs malware.\r\nOur Security Operations Centers are supported with Threat Intelligence, Tactical Threat Response and Advanced\r\nThreat Analytics driven by our Threat Response Unit – the TRU team.\r\nIn TRU Positives, eSentire’s Threat Response Unit (TRU) provides a summary of a recent threat investigation. We\r\noutline how we responded to the confirmed threat and what recommendations we have going forward.\r\nHere’s the latest from our TRU Team…\r\nWhat did we find?\r\nHow did we find it?\r\nOur Machine Learning PowerShell classifier detected malicious code execution resulting from the victim\r\nmanually executing the malicious VBS file.\r\nWhat did we do?\r\nOur 24/7 SOC cyber analysts alerted the customer and responded on the client’s behalf by successfully\r\nisolating the host.\r\nWhat can you learn from this TRU positive?\r\nThe HTML smuggling technique makes detection through content filters difficult since payloads are\r\nembedded within a local HTML file and not retrieved over the network.\r\nFurther complicating detection is the use of an .iso file within the HTML to hide the payload until mounted\r\nby the victim. Figure 5 shows a visual representation of this file structure.\r\nNote that only the email and final payload are transmitted over the network layer.\r\nhttps://www.esentire.com/blog/suspected-asyncrat-delivered-via-iso-files-using-html-smuggling-technique\r\nPage 1 of 6\n\nFigure 5 Visual representation of nested files.\r\nOur observations of adversaries using disk image files for code delivery is increasingly common. In\r\nFebruary TRU identified an IcedID campaign delivered using .iso images.\r\nMalware embedded inside of .iso files may evade security controls and is a known technique for bypassing\r\nthe Mark-of-the-Web trust control.\r\nEarly detection of this evasive malware delivery method will be crucial to limiting impact.\r\nRecommendations from our Threat Response Unit (TRU) Team:\r\nDisplay file extensions for known file types and consider showing hidden files to users by default.\r\nConduct Phishing and Security Awareness Training (PSAT) on a regular basis with your employees,\r\nplacing a special emphasis on spotting business email compromise (BEC) attacks. Warn users about the\r\nthreat posed by .html and image files (.iso) attached or hyperlinked in emails.\r\nCreate new “Open With” parameters for script files (.js, .jse, .hta, .vbs) so they open with notepad.exe. This\r\nsetting is found in the Group Policy Management Console under User\r\nConfiguration \u003e Preferences \u003e Control Panel Settings \u003e Folder Options.\r\nBy default, these script files are executed automatically using Windows Script Host (wscript.exe) or\r\nMicrosoft HTML Application host (mshta.exe) when double-clicked by a user.\r\nSince .iso files are mounted as a drive when double-clicked by users by default, consider deregistering this\r\nfile extension in Windows File Explorer.\r\nAsk Yourself\r\n1. What level of visibility do you have across your network, endpoint, and overall environment to detect\r\nmalicious behavior at scale?\r\n2. What tools are you employing for email filtering and how is that activity monitored?\r\nhttps://www.esentire.com/blog/suspected-asyncrat-delivered-via-iso-files-using-html-smuggling-technique\r\nPage 2 of 6\n\n3. What level of managed endpoint support do you have in place?\r\n4. Are you monitoring your endpoints 24/7 and what degree of control do you have to initiate a kill switch\r\nwhen required?\r\nIndicators of Compromise\r\ndca4d47ed0714d3ab9e4ef17192f7f1d “Order_Receipt.html”\r\nhttps://www[.]asterglobal[.]com/.Fainl.txt Location for payload retrieved by PowerShell command\r\nIf you’re not currently engaged with a Managed Detection and Response provider, we highly recommend you\r\npartner with us for security services in order to disrupt threats before they impact your business.\r\nWant to learn more? Connect with an eSentire Security Specialist.\r\nTo learn how your organization can build cyber resilience and prevent business disruption with eSentire’s Next\r\nLevel MDR, connect with an eSentire Security Specialist now.\r\nhttps://www.esentire.com/blog/suspected-asyncrat-delivered-via-iso-files-using-html-smuggling-technique\r\nPage 3 of 6\n\nGET STARTED\r\nABOUT ESENTIRE’S THREAT RESPONSE UNIT (TRU)\r\nThe eSentire Threat Response Unit (TRU) is an industry-leading threat research team committed to helping your\r\norganization become more resilient. TRU is an elite team of threat hunters and researchers that supports our 24/7\r\nSecurity Operations Centers (SOCs), builds threat detection models across the eSentire XDR Cloud Platform, and\r\nworks as an extension of your security team to continuously improve our Managed Detection and Response\r\nservice. By providing complete visibility across your attack surface and performing global threat sweeps and\r\nproactive hypothesis-driven threat hunts augmented by original threat research, we are laser-focused on defending\r\nyour organization against known and unknown threats.\r\nhttps://www.esentire.com/blog/suspected-asyncrat-delivered-via-iso-files-using-html-smuggling-technique\r\nPage 4 of 6\n\nBack to blog\r\nTake Your Cybersecurity Program to the Next Level with eSentire MDR.\r\nBUILD A QUOTE\r\nin this blog\r\nWhat did we find?How did we find it? What did we do? What can you learn from this TRU positive?\r\nRecommendations from our Threat Response Unit (TRU) Team:\r\nhttps://www.esentire.com/blog/suspected-asyncrat-delivered-via-iso-files-using-html-smuggling-technique\r\nPage 5 of 6\n\nSource: https://www.esentire.com/blog/suspected-asyncrat-delivered-via-iso-files-using-html-smuggling-technique\r\nhttps://www.esentire.com/blog/suspected-asyncrat-delivered-via-iso-files-using-html-smuggling-technique\r\nPage 6 of 6", "extraction_quality": 1, "language": "EN", "sources": [ "Malpedia" ], "origins": [ "web" ], "references": [ "https://www.esentire.com/blog/suspected-asyncrat-delivered-via-iso-files-using-html-smuggling-technique" ], "report_names": [ "suspected-asyncrat-delivered-via-iso-files-using-html-smuggling-technique" ], "threat_actors": [], "ts_created_at": 1775434353, "ts_updated_at": 1775826701, "ts_creation_date": 0, "ts_modification_date": 0, "files": { "pdf": "https://archive.orkl.eu/ee03eda84b004bb6ca0a939346c98310fe77067f.pdf", "text": "https://archive.orkl.eu/ee03eda84b004bb6ca0a939346c98310fe77067f.txt", "img": "https://archive.orkl.eu/ee03eda84b004bb6ca0a939346c98310fe77067f.jpg" } }