homepage
Open menu
Go one level top
  • Train and Certify
    Train and Certify

    Immediately apply the skills and techniques learned in SANS courses, ranges, and summits

    • Overview
    • Courses
      • Overview
      • Full Course List
      • By Focus Areas
        • Cloud Security
        • Cyber Defense
        • Cybersecurity and IT Essentials
        • DFIR
        • Industrial Control Systems
        • Offensive Operations
        • Management, Legal, and Audit
      • By Skill Levels
        • New to Cyber
        • Essentials
        • Advanced
        • Expert
      • Training Formats
        • OnDemand
        • In-Person
        • Live Online
      • Course Demos
    • Training Roadmaps
      • Skills Roadmap
      • Focus Area Job Roles
        • Cyber Defence Job Roles
        • Offensive Operations Job Roles
        • DFIR Job Roles
        • Cloud Job Roles
        • ICS Job Roles
        • Leadership Job Roles
      • NICE Framework
        • Security Provisionals
        • Operate and Maintain
        • Oversee and Govern
        • Protect and Defend
        • Analyze
        • Collect and Operate
        • Investigate
        • Industrial Control Systems
    • GIAC Certifications
    • Training Events & Summits
      • Events Overview
      • Event Locations
        • Asia
        • Australia & New Zealand
        • Latin America
        • Mainland Europe
        • Middle East & Africa
        • Scandinavia
        • United Kingdom & Ireland
        • United States & Canada
      • Summits
    • OnDemand
    • Get Started in Cyber
      • Overview
      • Degree and Certificate Programs
      • Scholarships
    • Cyber Ranges
  • Manage Your Team
    Manage Your Team

    Build a world-class cyber team with our workforce development programs

    • Overview
    • Why Work with SANS
    • Group Purchasing
    • Build Your Team
      • Team Development
      • Assessments
      • Private Training
      • Hire Cyber Professionals
      • By Industry
        • Health Care
        • Industrial Control Systems Security
        • Military
    • Leadership Training
  • Security Awareness
    Security Awareness

    Increase your staff’s cyber awareness, help them change their behaviors, and reduce your organizational risk

    • Overview
    • Products & Services
      • Security Awareness Training
        • EndUser Training
        • Phishing Platform
      • Specialized
        • Developer Training
        • ICS Engineer Training
        • NERC CIP Training
        • IT Administrator
      • Risk Assessments
        • Knowledge Assessment
        • Culture Assessment
        • Behavioral Risk Assessment
    • OUCH! Newsletter
    • Career Development
      • Overview
      • Training & Courses
      • Professional Credential
    • Blog
    • Partners
    • Reports & Case Studies
  • Resources
    Resources

    Enhance your skills with access to thousands of free resources, 150+ instructor-developed tools, and the latest cybersecurity news and analysis

    • Overview
    • Webcasts
    • Free Cybersecurity Events
      • Free Events Overview
      • Summits
      • Solutions Forums
      • Community Nights
    • Content
      • Newsletters
        • NewsBites
        • @RISK
        • OUCH! Newsletter
      • Blog
      • Podcasts
      • Summit Presentations
      • Posters & Cheat Sheets
    • Research
      • White Papers
      • Security Policies
    • Tools
    • Focus Areas
      • Cyber Defense
      • Cloud Security
      • Digital Forensics & Incident Response
      • Industrial Control Systems
      • Cyber Security Leadership
      • Offensive Operations
  • Get Involved
    Get Involved

    Help keep the cyber community one step ahead of threats. Join the SANS community or begin your journey of becoming a SANS Certified Instructor today.

    • Overview
    • Join the Community
    • Work Study
    • Teach for SANS
    • CISO Network
    • Partnerships
    • Sponsorship Opportunities
  • About
    About

    Learn more about how SANS empowers and educates current and future cybersecurity practitioners with knowledge and skills

    • SANS
      • Overview
      • Our Founder
      • Awards
    • Instructors
      • Our Instructors
      • Full Instructor List
    • Mission
      • Our Mission
      • Diversity
      • Scholarships
    • Contact
      • Contact Customer Service
      • Contact Sales
      • Press & Media Enquiries
    • Frequent Asked Questions
    • Customer Reviews
    • Press
    • Careers
  • Contact Sales
  • SANS Sites
    • GIAC Security Certifications
    • Internet Storm Center
    • SANS Technology Institute
    • Security Awareness Training
  • Search
  • Log In
  • Join
    • Account Dashboard
    • Log Out
  1. Home >
  2. Blog >
  3. Reverse Engineering Java
Craig Wright

Reverse Engineering Java

September 28, 2009

You have just come across a site compromise. You believe that the client was impacted due to a malicious java .class file on a rogue website that they visited. The class file is compiled, what can you do?

Luckily, java class files are simple to reverse engineer. In fact, using just the native JDK, the process could not be much simpler (the setting of classpath and ensuring that your java JDK is configured correctly is critical).

At the simplest, the process would be to use the command:

javac -c classfile

    The '-c' option is used to specify that you want to decompile the java bytecode.

    The term 'classfile' is where you specify the file that you are seeking to decode.

    When reversing java based malware, the chances are that the code will have been obscured. This means that the stages above are not the totality of accessing the code. Compression and cryptors are some of the methods deployed. This will add a layer of obsfucation to the code.

    For instance, a compressed class file could be called by the code you have decoded. This initial layer of code would hence form a shell that makes the code that actually did the damage harder to analyze. On top of this, a few simple techniques (such as using Unicode to hide strings) can be deployed.

    You may not get a native java file, but at least you have the constructors and variables used and this gets you a long way into understanding the code.

    Craig Wright is a Director with Information Defense in Australia. He holds both the GSE-Malware and GSE-Compliance certifications from GIAC. He is a perpetual student with numerous post graduate degrees including an LLM specializing in international commercial law and ecommerce law as well as working on his 4th IT focused Masters degree (Masters in System Development) from Charles Stuart University where he is helping to launch a Masters degree in digital forensics. He is engaged in his second doctorate, a PhD on the quantification of information system risk at CSU.

    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
    Croatia (Local Name: Hrvatska)
    Curacao
    Cyprus
    Czech Republic
    Democratic Republic of the Congo
    Djibouti
    Dominica
    Dominican Republic
    East Timor
    East Timor
    Ecuador
    Egypt
    El Salvador
    Equatorial Guinea
    Eritrea
    Estonia
    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
    Macedonia
    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
    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
    Swaziland
    Sweden
    Switzerland
    Taiwan
    Tajikistan
    Tanzania
    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
    Venezuela
    Vietnam
    Virgin Islands (British)
    Virgin Islands (U.S.)
    Wallis And Futuna Islands
    Western Sahara
    Yemen
    Yugoslavia
    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 and Incident Response

    Related Content

    Blog
    Top_10_Summit_Talks_2022.png
    Cybersecurity Insights, Digital Forensics and Incident Response, Cyber Defense, Cloud Security, Open-Source Intelligence (OSINT), Security Management, Legal, and Audit, Security Awareness
    December 5, 2022
    Top 10 SANS Summits Talks of 2022
    This year, SANS hosted 13 Summits with 246 talks. Here were the top-rated talks of the year.
    370x370-person-placeholder.png
    Alison Kim
    read more
    Blog
    FOR577.png
    Digital Forensics and Incident Response
    September 22, 2022
    NEW SANS DFIR COURSE IN DEVELOPMENT | FOR577: LINUX Incident Response & Analysis
    FOR577: Linux Incident Response & Analysis course teaches how Linux systems work and how to respond and investigate attacks effectively.
    Viv_Ross_370x370.png
    Viviana Ross
    read more
    Blog
    Untitled_design-43.png
    Digital Forensics and Incident Response, Cybersecurity and IT Essentials, Industrial Control Systems Security, Purple Team, Open-Source Intelligence (OSINT), Penetration Testing and Red Teaming, Cyber Defense, Cloud Security, Security Management, Legal, and Audit
    December 8, 2021
    Good News: SANS Virtual Summits Will Remain FREE for the Community in 2022
    They’re virtual. They’re global. They’re free.
    370x370-person-placeholder.png
    Emily Blades
    read more
    • Register to Learn
    • Courses
    • Certifications
    • Degree Programs
    • Cyber Ranges
    • Job Tools
    • Security Policy Project
    • Posters & Cheat Sheets
    • White Papers
    • Focus Areas
    • Cyber Defense
    • Cloud Security
    • Cybersecurity Leadership
    • Digital Forensics
    • Industrial Control Systems
    • Offensive Operations
    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
    Croatia (Local Name: Hrvatska)
    Curacao
    Cyprus
    Czech Republic
    Democratic Republic of the Congo
    Djibouti
    Dominica
    Dominican Republic
    East Timor
    East Timor
    Ecuador
    Egypt
    El Salvador
    Equatorial Guinea
    Eritrea
    Estonia
    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
    Macedonia
    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
    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
    Swaziland
    Sweden
    Switzerland
    Taiwan
    Tajikistan
    Tanzania
    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
    Venezuela
    Vietnam
    Virgin Islands (British)
    Virgin Islands (U.S.)
    Wallis And Futuna Islands
    Western Sahara
    Yemen
    Yugoslavia
    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.
    • © 2023 SANS™ Institute
    • Privacy Policy
    • Contact
    • Careers
    • Twitter
    • Facebook
    • Youtube
    • LinkedIn