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	"title": "Looking at Mutex Objects for Malware Discovery \u0026 Indicators of Compromise",
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	"authors": "",
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	"plain_text": "Looking at Mutex Objects for Malware Discovery \u0026 Indicators of\r\nCompromise\r\nBy Lenny Zeltser\r\nPublished: 2012-07-24 · Archived: 2026-04-05 16:14:48 UTC\r\nMutex (a.k.a. mutant) objects, which are frequently used by legitimate software, can also help defenders discover\r\nthe presence of malicious programs on the system. Incident responders can examine the infected host or reverse-engineer malware to identify mutex names used by the specimen, which will allow them to define the signs of the\r\ninfection (a.k.a. indicators of compromise). Let's take a look at how mutex objects are used and what tools are\r\navailable to identify them on a system.\r\nHow Programs Use Mutex Objects\r\nPrograms use mutex (\"mutual exclusion\") objects as a locking mechanism to serialize access to a resource on the\r\nsystem. Consider the following explanation by Microsoft: \"For example, to prevent two threads from writing to\r\nshared memory at the same time, each thread waits for ownership of a mutex object before executing the code that\r\naccesses the memory. After writing to the shared memory, the thread releases the mutex object.\"\r\nThe Use of Mutex Objects by Malware\r\nMalicious software often uses mutex objects for the same purpose as legitimate software. Furthermore, malware\r\nmight use a mutex to avoid reinfecting the host. For instance, the specimen might attempt to open a handle to a\r\nmutex with a specific name. The specimen might exit if the mutex exists, because the host is already infected.\r\nConsider the renowned Flame malware. According to FireEye, one of this specimen's components created\r\n\"numerous mutexes in order to synchronize copies of itself simultaneously injected into various core Windows\r\nprocesses (e.g., services.exe, iexplore.exe, winlogon.exe) that are already running.\" FireEye documented the\r\nmutex names whose presence indicated that the system was infected with Flame.\r\nAs another example, the Pushdo/Cutwail bot created mutex objects that were used to \"coordinate its highly\r\nmultithreaded communication\" according to TrendMicro. The mutex objects names were \"gangrenb,\" \"germeonb,\"\r\n\"crypt32LogOffPortEvent,\" etc. As yet another example, the default name of the mutex set by the popular Poison\r\nIvy backdoor is \")!VoqA.I4\"; this was the case during a targeted attack against a large Swedish company\r\ndocumented by the Internet Storm Center.\r\nIn some cases, malware might dynamically generate mutex names in an attempt to evade detection.\r\nUsing Mutex Values to Find Malware\r\nWhen examining a potentially-infected system, we can look for names of mutex objects known to belong to\r\nmalicious programs. This approach works particularly well when you've already identified malware on some\r\nhttps://www.sans.org/blog/looking-at-mutex-objects-for-malware-discovery-indicators-of-compromise/\r\nPage 1 of 3\n\nenterprise system, determined the names of its mutex objects, and are examining other systems to see whether\r\nthey are infected. Malware databases such as ThreatExpert include mutex names when describing malware,\r\nproviding another source of potential signatures based on mutex objects.\r\nMoreover, it's relatively uncommon for legitimate programs to use mutex names that are completely random; you\r\nmight use this heuristic to identify infected hosts even without searching for a specific mutex names. (See Gary\r\nGolomb's post that touches upon this topic.) A command-line tool called CheckMutex can query the local host for\r\nthe presence of a mutex object with a specific name. The author of CheckMutex, Jaime Blasco, also provides a\r\ncommand-line utility called EnumerateMutex for generating a list of all active mutex objects on the system, you\r\nyou can examine the list for the names that interest you.\r\nAnother way to enumerate all mutex objects from the command line involves Microsoft's Handletool by Mark\r\nRussinovich. This utility lists various handle types that are open on the system; to list only mutex objects look for\r\nthose of type \"Mutant\" like this:\r\nGUI tools Process Explorer and Process Hacker tools can list open handles on the host, including those that refer\r\nto mutex objects. Both tools include an option to search for an open handle or DLL by name. The Performance\r\nMonitor tool, built into Windows, also offers these capabilities, as outlined by Mark Baggett. Here's what this\r\nfeature looks like in Process Hacker:\r\nIt is also possible to search for mutex names when examining a memory snapshot of a compromised system. For\r\ninstance, the popular memory forensics framework Volatility can enumerate mutant values using the \"mutantscan\"\r\ncommand.\r\nFor another potential use of mutex values, consider the possibility of proactively generating mutant objects, so\r\nthat malware believes it is already active on the host and refuses detection. I discussed this idea in the article\r\nContemplating Malware Immunization via Infection Markers.\r\nAs you saw in this article, mutex names can be used for creating indicators of compromise, which would allow\r\nincident responders to identify hosts infected with malware that uses those mutex objects. It might also be possible\r\nto define heuristics that alert when unusually-random mutex names are discovered on the host, though this\r\napproach could produce some false positives. There are several command-line tools to list mutex names, though\r\nthere is room for maturing this approach to malware discovery.\r\nhttps://www.sans.org/blog/looking-at-mutex-objects-for-malware-discovery-indicators-of-compromise/\r\nPage 2 of 3\n\nLenny Zeltser teaches malware analysis at SANS Institute. At the \"day job,\" Lenny focuses on safeguarding\r\ncustomers' IT operations at NCR Corp. He is active on Twitter and writes a security blog.\r\nSource: https://www.sans.org/blog/looking-at-mutex-objects-for-malware-discovery-indicators-of-compromise/\r\nhttps://www.sans.org/blog/looking-at-mutex-objects-for-malware-discovery-indicators-of-compromise/\r\nPage 3 of 3",
	"extraction_quality": 1,
	"language": "EN",
	"sources": [
		"MITRE"
	],
	"references": [
		"https://www.sans.org/blog/looking-at-mutex-objects-for-malware-discovery-indicators-of-compromise/"
	],
	"report_names": [
		"looking-at-mutex-objects-for-malware-discovery-indicators-of-compromise"
	],
	"threat_actors": [],
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	"ts_updated_at": 1775791292,
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