{
	"id": "245d29a9-3dd7-4660-bd6e-69df6d256b6a",
	"created_at": "2026-04-06T00:11:51.834939Z",
	"updated_at": "2026-04-10T03:21:17.903156Z",
	"deleted_at": null,
	"sha1_hash": "7fca1182bde993ce08bd142ea2e2cd281bf89a9e",
	"title": "Phishing Attacks Using Verclsid.exe: Threat Detection",
	"llm_title": "",
	"authors": "",
	"file_creation_date": "0001-01-01T00:00:00Z",
	"file_modification_date": "0001-01-01T00:00:00Z",
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	"plain_text": "Phishing Attacks Using Verclsid.exe: Threat Detection\r\nBy Keshia LeVan, Michael Haag\r\nArchived: 2026-04-05 18:37:15 UTC\r\nPhishing is not exactly a new or groundbreaking attack method, but it’s an ongoing problem (likely because it’s\r\neffective and we all need e-mail). A wave of Hancitor malware spam campaigns recently hit many organizations.\r\nIt’s your typical pattern: a non-descriptively named Microsoft Word document sent with email subject lines like\r\n“USPS” or “eFax” using macros and heavily obfuscated VBScript to initiate the download of a malicious payload.\r\nWhat’s interesting is not that an Office document is yet again being used to do something untoward…what’s\r\nnotable is the method being used. Normally you would expect to see something like PowerShell, WScript, or\r\nmaybe just a plain old command prompt. Instead, a completely different process is launched: verclsid.exe.\r\nWhat Is Verclsid.exe?\r\nIf you’re like us, you probably never heard of verclsid.exe until malware started using it. According to Microsoft,\r\nthis program was created to “validate shell extensions before they are instantiated by the Windows shell or\r\nWindows Explorer.” We’re not entirely sure what exactly this means, but we think the gist was to check COM\r\nextensions to see if they would crash explorer.exe.\r\nIt was released back in 2006 to mitigate a Remote Code Execution Vulnerability (MS06-015 – 908531) for XP\r\nand Server 2003 era systems. However, just to be clear, this isn’t just running on XP systems; the process has\r\npersisted into modern operating systems. To be sure, we checked the file system and sure enough found\r\nverclsid.exe alive and well on our Windows 10 host. Though it’s not explicitly stated why, there is a whole lot of\r\nbackwards compatibility that Microsoft does under the surface. This can be both good and bad depending on what\r\nyou’re trying to do, so banning the process outright is probably not the best plan.\r\nRegardless of its true purpose, what is clear is that verclsid.exe can do things like initiate network connections and\r\ndownload and write files to disk, as evidenced by the below activity, which was observed on a compromised host:\r\nhttps://redcanary.com/blog/verclsid-exe-threat-detection/\r\nPage 1 of 4\n\nWhat to Do Next: Investigating Endpoint Data\r\nSo we know that verclsid.exe can be used nefariously, but that in and of itself is not terribly helpful. You could try\r\nto read the documentation on it, but you’d probably quickly discover that the Microsoft information on this\r\nparticular process isn’t incredibly voluminous. The question, then, is “What’s next?” Maybe the real goal is not in\r\nknowing absolutely everything a process can do, but what does it normally do? We attempted to see if there were\r\nany outliers that only happen when it is being used to download and execute malware. Luckily for our\r\ninvestigative purposes, we had a fairly decent dataset of what abnormal behavior looked like across several\r\ncustomers that had been hit by this Hancitor variant, so we already probably had the outliers; we just needed to\r\ndetermine what they were and if they could be used to create a useful detection method.\r\nIn this case, having a good amount of diverse endpoint data can give us a lot of insight into a random process—in\r\nthis case verclsid.exe. To start things off we looked at what verclsid.exe does most of the time, in a single\r\nenvironment where no malicious activity had been observed, with 193,000+ total executions of the process. The\r\nfollowing table depicts the range of activity we found.[table id=1 /]\r\nA couple things immediately jump out. First, this process never makes a network connection and it never launches\r\nany child processes. Filemod is a potential candidate, but since we’re only looking at range data here and not\r\nfrequency, we don’t know right off the bat if it’s very common for verclsid.exe to only write one filemod every\r\ntime.\r\nhttps://redcanary.com/blog/verclsid-exe-threat-detection/\r\nPage 2 of 4\n\nLet’s go back to our known bad example. We can see that it has a total of five network connections and three child\r\nprocesses. Likely, there’s something we can use here. A lot of what we do at Red Canary is to view things from the\r\nlens of “How do we detect this activity?” In this case, making a rule like “anytime verclsid.exe initiates a network\r\nconnection, let me know” seems like a good start. Since it almost never launches network connections in normal\r\nday-to-day use, that rule will likely also have a low false positive rate (which is always nice).\r\nA second option for detection is to look at what process launches verclsid.exe. If it’s almost never a Microsoft\r\nOffice binary, that could be a good detection rule as well.\r\nDetection is all well and good, but most folks would rather that the ‘badness’ never touched their systems in the\r\nhttps://redcanary.com/blog/verclsid-exe-threat-detection/\r\nPage 3 of 4\n\nfirst place, and if the payload isn’t delivered as part of the phishing e-mail, it has to be gotten from elsewhere (i.e.,\r\nthe web). So the next question is: can you stop verclsid.exe from making a network connection in the first place?\r\nHow to Prevent Verclsid.exe From Malicious Activity\r\nWhen verclsid.exe is used for its intended purpose, it doesn’t need to make a network connection (at least in our\r\nsample set), so why not put something in place that prevents this? That way, even if the initial drop on a system is\r\nsuccessful, the subsequent download simply will not happen. Turns out, you can do this—and it doesn’t require\r\nany high tech expensive tool. Simply go back to the Windows Firewall conveniently built in into any (or nearly\r\nany) modern version of Windows.\r\nAdd the following rule (and a second one for ‘%SystemRoot%\\system32\\verclsid.exe’) to prevent this process\r\nfrom talking outbound.\r\nnetsh advfirewall firewall add rule name \"Block Egress Verclsid\" dir=out\r\nprogram=\"%SystemRoot%\\syswow64\\verclsid.exe\" enable=yes action=block profile=any\r\nThis can of course be implemented via GPO.\r\nKey Takeaways for Defenders\r\nThis is just one example of a way that defenders can (at least partially) mitigate attacks that are very likely to get\r\nthrough perimeter defenses. After all, most organizations need (or prefer) Microsoft Office. (Mac users, you’re not\r\nexactly safe here either; while vbscript and verclsid.exe are not an issue, you have osascript and python, so…)\r\nThe important takeaway is not necessarily to focus specifically on verclsid.exe, as implementing one specific rule\r\nwill not fix everything. The key lessons are that (a) there are ways to identify when a process is doing something\r\nand alert on it, and; (b) sometimes you can use tools (sometimes even built-in OS ones) to mitigate the impact of\r\nattacks that do make it past the perimeter.\r\nSource: https://redcanary.com/blog/verclsid-exe-threat-detection/\r\nhttps://redcanary.com/blog/verclsid-exe-threat-detection/\r\nPage 4 of 4",
	"extraction_quality": 1,
	"language": "EN",
	"sources": [
		"MITRE"
	],
	"references": [
		"https://redcanary.com/blog/verclsid-exe-threat-detection/"
	],
	"report_names": [
		"verclsid-exe-threat-detection"
	],
	"threat_actors": [],
	"ts_created_at": 1775434311,
	"ts_updated_at": 1775791277,
	"ts_creation_date": 0,
	"ts_modification_date": 0,
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