homepage
Menu
Open menu
  • Training
    Go one level top Back

    Training

    • Courses

      Build cyber prowess with training from renowned experts

    • Hands-On Simulations

      Hands-on learning exercises keep you at the top of your cyber game

    • Certifications

      Demonstrate cybersecurity expertise with GIAC certifications

    • Ways to Train

      Multiple training options to best fit your schedule and preferred learning style

    • Training Events & Summits

      Expert-led training at locations around the world

    • Free Training Events

      Upcoming workshops, webinars and local events

    • Security Awareness

      Harden enterprise security with end-user and role-based training

    Featured: Solutions for Emerging Risks

    Discover tailored resources that translate emerging threats into actionable strategies

    Risk-Based Solutions

    Can't find what you are looking for?

    Let us help.
    Contact us
  • Learning Paths
    Go one level top Back

    Learning Paths

    • By Focus Area

      Chart your path to job-specific training courses

    • By NICE Framework

      Navigate cybersecurity training through NICE framework roles

    • DoDD 8140 Work Roles

      US DoD 8140 Directive Frameworks

    • By European Skills Framework

      Align your enterprise cyber skills with ECSF profiles

    • By Skills Roadmap

      Find the right training path based on critical skills

    • New to Cyber

      Give your cybersecurity career the right foundation for success

    • Leadership

      Training designed to help security leaders reduce organizational risk

    • Degree and Certificate Programs

      Gain the skills, certifications, and confidence to launch or advance your cybersecurity career.

    Featured

    New to Cyber resources

    Start your career
  • Community Resources
    Go one level top Back

    Community Resources

    Watch & Listen

    • Webinars
    • Live Streams
    • Podcasts

    Read

    • Blog
    • Newsletters
    • White Papers
    • Internet Storm Center

    Download

    • Open Source Tools
    • Posters & Cheat Sheets
    • Policy Templates
    • Summit Presentations
    • SANS Community Benefits

      Connect, learn, and share with other cybersecurity professionals

    • CISO Network

      Engage, challenge, and network with fellow CISOs in this exclusive community of security leaders

  • For Organizations
    Go one level top Back

    For Organizations

    Team Development

    • Why Partner with SANS
    • Group Purchasing
    • Skills & Talent Assessments
    • Private & Custom Training

    Leadership Development

    • Leadership Courses & Accreditation
    • Executive Cybersecurity Exercises
    • CISO Network

    Security Awareness

    • End-User Training
    • Phishing Simulation
    • Specialized Role-Based Training
    • Risk Assessments
    • Public Sector Partnerships

      Explore industry-specific programming and customized training solutions

    • Sponsorship Opportunities

      Sponsor a SANS event or research paper

    Interested in developing a training plan to fit your organization’s needs?

    We're here to help.
    Contact us
  • Talk with an expert
  • Log In
  • Join - it's free
  • Account
    • Account Dashboard
    • Log Out
  1. Home >
  2. Blog >
  3. Looking at Mutex Objects for Malware Discovery & Indicators of Compromise
Lenny_Portrait_New_370x370.jpg
Lenny Zeltser

Looking at Mutex Objects for Malware Discovery & Indicators of Compromise

Mutex (a.k.a. mutant) objects, which are frequently used by legitimate software, can also help defenders discover...

July 24, 2012

Mutex (a.k.a. mutant) objects, which are frequently used by legitimate software, can also help defenders discover the 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 infection (a.k.a. indicators of compromise). Let's take a look at how mutex objects are used and what tools are available to identify them on a system.

How Programs Use Mutex Objects

Programs use mutex ("mutual exclusion") objects as a locking mechanism to serialize access to a resource on the system. Consider the following explanation by Microsoft: "For example, to prevent two threads from writing to shared memory at the same time, each thread waits for ownership of a mutex object before executing the code that accesses the memory. After writing to the shared memory, the thread releases the mutex object."

The Use of Mutex Objects by Malware

Malicious software often uses mutex objects for the same purpose as legitimate software. Furthermore, malware might use a mutex to avoid reinfecting the host. For instance, the specimen might attempt to open a handle to a mutex with a specific name. The specimen might exit if the mutex exists, because the host is already infected.

Consider the renowned Flame malware. According to FireEye, one of this specimen's components created "numerous mutexes in order to synchronize copies of itself simultaneously injected into various core Windows processes (e.g., services.exe, iexplore.exe, winlogon.exe) that are already running." FireEye documented the mutex names whose presence indicated that the system was infected with Flame.

As another example, the Pushdo/Cutwail bot created mutex objects that were used to "coordinate its highly multithreaded communication" according to TrendMicro. The mutex objects names were "gangrenb," "germeonb," "crypt32LogOffPortEvent," etc. As yet another example, the default name of the mutex set by the popular Poison Ivy backdoor is ")!VoqA.I4"; this was the case during a targeted attack against a large Swedish company documented by the Internet Storm Center.

In some cases, malware might dynamically generate mutex names in an attempt to evade detection.

Using Mutex Values to Find Malware

When examining a potentially-infected system, we can look for names of mutex objects known to belong to malicious programs. This approach works particularly well when you've already identified malware on some enterprise system, determined the names of its mutex objects, and are examining other systems to see whether they are infected. Malware databases such as ThreatExpert include mutex names when describing malware, providing another source of potential signatures based on mutex objects.

Moreover, it's relatively uncommon for legitimate programs to use mutex names that are completely random; you might use this heuristic to identify infected hosts even without searching for a specific mutex names. (See Gary Golomb's post that touches upon this topic.) A command-line tool called CheckMutex can query the local host for the presence of a mutex object with a specific name. The author of CheckMutex, Jaime Blasco, also provides a command-line utility called EnumerateMutex for generating a list of all active mutex objects on the system, you you can examine the list for the names that interest you.

Another way to enumerate all mutex objects from the command line involves Microsoft's Handletool by Mark Russinovich. This utility lists various handle types that are open on the system; to list only mutex objects look for those of type "Mutant" like this:

handle -a | findstr Mutant

GUI tools Process Explorer and Process Hacker tools can list open handles on the host, including those that refer to mutex objects. Both tools include an option to search for an open handle or DLL by name. The Performance Monitor tool, built into Windows, also offers these capabilities, as outlined by Mark Baggett. Here's what this feature looks like in Process Hacker:

find-handles.png

It is also possible to search for mutex names when examining a memory snapshot of a compromised system. For instance, the popular memory forensics framework Volatility can enumerate mutant values using the "mutantscan" command.

For another potential use of mutex values, consider the possibility of proactively generating mutant objects, so that malware believes it is already active on the host and refuses detection. I discussed this idea in the article Contemplating Malware Immunization via Infection Markers.

As you saw in this article, mutex names can be used for creating indicators of compromise, which would allow incident responders to identify hosts infected with malware that uses those mutex objects. It might also be possible to define heuristics that alert when unusually-random mutex names are discovered on the host, though this approach could produce some false positives. There are several command-line tools to list mutex names, though there is room for maturing this approach to malware discovery.

Related posts:

  • Context-Specific Signatures for Computer Security Incident Response
  • 3 Tools to Scan the File System With Custom Malware Signatures

Lenny Zeltser teaches malware analysis at SANS Institute. At the "day job," Lenny focuses on safeguarding customers' IT operations at NCR Corp. He is active on Twitter and writes a security blog.

Share:
TwitterLinkedInFacebook
Copy url Url was copied to clipboard
Subscribe to SANS Newsletters
Receive curated news, vulnerabilities, & security awareness tips
United States
Canada
United Kingdom
Spain
Belgium
Denmark
Norway
Netherlands
Australia
India
Japan
Singapore
Afghanistan
Aland Islands
Albania
Algeria
American Samoa
Andorra
Angola
Anguilla
Antarctica
Antigua and Barbuda
Argentina
Armenia
Aruba
Austria
Azerbaijan
Bahamas
Bahrain
Bangladesh
Barbados
Belarus
Belize
Benin
Bermuda
Bhutan
Bolivia
Bonaire, Sint Eustatius, and Saba
Bosnia And Herzegovina
Botswana
Bouvet Island
Brazil
British Indian Ocean Territory
Brunei Darussalam
Bulgaria
Burkina Faso
Burundi
Cambodia
Cameroon
Cape Verde
Cayman Islands
Central African Republic
Chad
Chile
China
Christmas Island
Cocos (Keeling) Islands
Colombia
Comoros
Cook Islands
Costa Rica
Cote D'ivoire
Croatia (Local Name: Hrvatska)
Curacao
Cyprus
Czech Republic
Democratic Republic of the Congo
Djibouti
Dominica
Dominican Republic
East Timor
Ecuador
Egypt
El Salvador
Equatorial Guinea
Eritrea
Estonia
Eswatini
Ethiopia
Falkland Islands (Malvinas)
Faroe Islands
Fiji
Finland
France
French Guiana
French Polynesia
French Southern Territories
Gabon
Gambia
Georgia
Germany
Ghana
Gibraltar
Greece
Greenland
Grenada
Guadeloupe
Guam
Guatemala
Guernsey
Guinea
Guinea-Bissau
Guyana
Haiti
Heard And McDonald Islands
Honduras
Hong Kong
Hungary
Iceland
Indonesia
Iraq
Ireland
Isle of Man
Israel
Italy
Jamaica
Jersey
Jordan
Kazakhstan
Kenya
Kiribati
Korea, Republic Of
Kosovo
Kuwait
Kyrgyzstan
Lao People's Democratic Republic
Latvia
Lebanon
Lesotho
Liberia
Liechtenstein
Lithuania
Luxembourg
Macau
Madagascar
Malawi
Malaysia
Maldives
Mali
Malta
Marshall Islands
Martinique
Mauritania
Mauritius
Mayotte
Mexico
Micronesia, Federated States Of
Moldova, Republic Of
Monaco
Mongolia
Montenegro
Montserrat
Morocco
Mozambique
Myanmar
Namibia
Nauru
Nepal
Netherlands Antilles
New Caledonia
New Zealand
Nicaragua
Niger
Nigeria
Niue
Norfolk Island
North Macedonia
Northern Mariana Islands
Oman
Pakistan
Palau
Palestine
Panama
Papua New Guinea
Paraguay
Peru
Philippines
Pitcairn
Poland
Portugal
Puerto Rico
Qatar
Reunion
Romania
Russian Federation
Rwanda
Saint Bartholemy
Saint Kitts And Nevis
Saint Lucia
Saint Martin
Saint Vincent And The Grenadines
Samoa
San Marino
Sao Tome And Principe
Saudi Arabia
Senegal
Serbia
Seychelles
Sierra Leone
Sint Maarten
Slovakia
Slovenia
Solomon Islands
South Africa
South Georgia and the South Sandwich Islands
South Sudan
Sri Lanka
St. Helena
St. Pierre And Miquelon
Suriname
Svalbard And Jan Mayen Islands
Sweden
Switzerland
Taiwan
Tajikistan
Tanzania, United Republic Of
Thailand
Togo
Tokelau
Tonga
Trinidad And Tobago
Tunisia
Turkey
Turkmenistan
Turks And Caicos Islands
Tuvalu
Uganda
Ukraine
United Arab Emirates
United States Minor Outlying Islands
Uruguay
Uzbekistan
Vanuatu
Vatican City State
Venezuela
Vietnam
Virgin Islands (British)
Virgin Islands (U.S.)
Wallis And Futuna Islands
Western Sahara
Yemen
Zambia
Zimbabwe

By providing this information, you agree to the processing of your personal data by SANS as described in our Privacy Policy.

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.

Tags:
  • Digital Forensics, Incident Response & Threat Hunting

Related Content

Blog
emerging threats summit 340x340.png
Digital Forensics, Incident Response & Threat Hunting, Offensive Operations, Pen Testing, and Red Teaming, Cyber Defense, Industrial Control Systems Security, Cybersecurity Leadership
May 14, 2025
Visual Summary of SANS Emerging Threats Summit 2025
Check out these graphic recordings created in real-time throughout the event for SANS Emerging Threats Summit 2025
No Headshot Available
Alison Kim
read more
Blog
DFIR - Blog - Running EZ Tools Natively on Linux_340 x 340.jpg
Digital Forensics, Incident Response & Threat Hunting
April 23, 2025
Running EZ Tools Natively on Linux: A Step-by-Step Guide
Developed by Eric Zimmerman, the EZ Tools suite is a collection of utilities written to assist with multiple aspects of forensic analysis.
Seth_Enoka_370x370.png
Seth Enoka
read more
Blog
powershell_option_340x340.jpg
Cyber Defense, Digital Forensics, Incident Response & Threat Hunting, Cybersecurity and IT Essentials, Offensive Operations, Pen Testing, and Red Teaming
July 12, 2022
Month of PowerShell - Windows File Server Enumeration
In this Month of PowerShell article we look at several commands to interrogate Windows SMB servers as part of our incident response toolkit.
Josh Wright - Headshot - 370x370 2025.jpg
Joshua Wright
read more
  • Company
  • Mission
  • Instructors
  • About
  • FAQ
  • Press
  • Contact Us
  • Careers
  • Policies
  • Training Programs
  • Work Study
  • Academies & Scholarships
  • Public Sector Partnerships
  • Law Enforcement
  • SkillsFuture Singapore
  • Degree Programs
  • Get Involved
  • Join the Community
  • Become an Instructor
  • Become a Sponsor
  • Speak at a Summit
  • Join the CISO Network
  • Award Programs
  • Partner Portal
Subscribe to SANS Newsletters
Receive curated news, vulnerabilities, & security awareness tips
United States
Canada
United Kingdom
Spain
Belgium
Denmark
Norway
Netherlands
Australia
India
Japan
Singapore
Afghanistan
Aland Islands
Albania
Algeria
American Samoa
Andorra
Angola
Anguilla
Antarctica
Antigua and Barbuda
Argentina
Armenia
Aruba
Austria
Azerbaijan
Bahamas
Bahrain
Bangladesh
Barbados
Belarus
Belize
Benin
Bermuda
Bhutan
Bolivia
Bonaire, Sint Eustatius, and Saba
Bosnia And Herzegovina
Botswana
Bouvet Island
Brazil
British Indian Ocean Territory
Brunei Darussalam
Bulgaria
Burkina Faso
Burundi
Cambodia
Cameroon
Cape Verde
Cayman Islands
Central African Republic
Chad
Chile
China
Christmas Island
Cocos (Keeling) Islands
Colombia
Comoros
Cook Islands
Costa Rica
Cote D'ivoire
Croatia (Local Name: Hrvatska)
Curacao
Cyprus
Czech Republic
Democratic Republic of the Congo
Djibouti
Dominica
Dominican Republic
East Timor
Ecuador
Egypt
El Salvador
Equatorial Guinea
Eritrea
Estonia
Eswatini
Ethiopia
Falkland Islands (Malvinas)
Faroe Islands
Fiji
Finland
France
French Guiana
French Polynesia
French Southern Territories
Gabon
Gambia
Georgia
Germany
Ghana
Gibraltar
Greece
Greenland
Grenada
Guadeloupe
Guam
Guatemala
Guernsey
Guinea
Guinea-Bissau
Guyana
Haiti
Heard And McDonald Islands
Honduras
Hong Kong
Hungary
Iceland
Indonesia
Iraq
Ireland
Isle of Man
Israel
Italy
Jamaica
Jersey
Jordan
Kazakhstan
Kenya
Kiribati
Korea, Republic Of
Kosovo
Kuwait
Kyrgyzstan
Lao People's Democratic Republic
Latvia
Lebanon
Lesotho
Liberia
Liechtenstein
Lithuania
Luxembourg
Macau
Madagascar
Malawi
Malaysia
Maldives
Mali
Malta
Marshall Islands
Martinique
Mauritania
Mauritius
Mayotte
Mexico
Micronesia, Federated States Of
Moldova, Republic Of
Monaco
Mongolia
Montenegro
Montserrat
Morocco
Mozambique
Myanmar
Namibia
Nauru
Nepal
Netherlands Antilles
New Caledonia
New Zealand
Nicaragua
Niger
Nigeria
Niue
Norfolk Island
North Macedonia
Northern Mariana Islands
Oman
Pakistan
Palau
Palestine
Panama
Papua New Guinea
Paraguay
Peru
Philippines
Pitcairn
Poland
Portugal
Puerto Rico
Qatar
Reunion
Romania
Russian Federation
Rwanda
Saint Bartholemy
Saint Kitts And Nevis
Saint Lucia
Saint Martin
Saint Vincent And The Grenadines
Samoa
San Marino
Sao Tome And Principe
Saudi Arabia
Senegal
Serbia
Seychelles
Sierra Leone
Sint Maarten
Slovakia
Slovenia
Solomon Islands
South Africa
South Georgia and the South Sandwich Islands
South Sudan
Sri Lanka
St. Helena
St. Pierre And Miquelon
Suriname
Svalbard And Jan Mayen Islands
Sweden
Switzerland
Taiwan
Tajikistan
Tanzania, United Republic Of
Thailand
Togo
Tokelau
Tonga
Trinidad And Tobago
Tunisia
Turkey
Turkmenistan
Turks And Caicos Islands
Tuvalu
Uganda
Ukraine
United Arab Emirates
United States Minor Outlying Islands
Uruguay
Uzbekistan
Vanuatu
Vatican City State
Venezuela
Vietnam
Virgin Islands (British)
Virgin Islands (U.S.)
Wallis And Futuna Islands
Western Sahara
Yemen
Zambia
Zimbabwe

By providing this information, you agree to the processing of your personal data by SANS as described in our Privacy Policy.

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
  • Privacy Policy
  • Terms and Conditions
  • Do Not Sell/Share My Personal Information
  • Contact
  • Careers
© 2025 The Escal Institute of Advanced Technologies, Inc. d/b/a SANS Institute. Our Terms and Conditions detail our trademark and copyright rights. Any unauthorized use is expressly prohibited.
  • Twitter
  • Facebook
  • Youtube
  • LinkedIn