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<ol class="chapter"><li class="chapter-item expanded "><a href="../../Introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li class="chapter-item expanded "><a href="../../manual/Installing.html"><strong aria-hidden="true">2.</strong> Installing</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../../manual/Installing/Packages.html"><strong aria-hidden="true">2.1.</strong> Packages</a></li><li class="chapter-item expanded "><a href="../../manual/Installing/Docker.html"><strong aria-hidden="true">2.2.</strong> Docker</a></li><li class="chapter-item expanded "><a href="../../manual/Installing/Installing-from-source-Unix.html"><strong aria-hidden="true">2.3.</strong> Unix from source (v0.104+)</a></li><li class="chapter-item expanded "><a href="../../manual/Installing/Installing-from-source-Unix-old.html"><strong aria-hidden="true">2.4.</strong> Unix from source (v0.103-)</a></li><li class="chapter-item expanded "><a href="../../manual/Installing/Installing-from-source-Windows.html"><strong aria-hidden="true">2.5.</strong> Windows from source</a></li><li class="chapter-item expanded "><a href="../../manual/Installing/Community-projects.html"><strong aria-hidden="true">2.6.</strong> Community Projects</a></li><li class="chapter-item expanded "><a href="../../manual/Installing/Add-clamav-user.html"><strong aria-hidden="true">2.7.</strong> Add a service user account</a></li></ol></li><li class="chapter-item expanded "><a href="../../manual/Usage.html"><strong aria-hidden="true">3.</strong> Usage</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../../manual/Usage/Configuration.html"><strong aria-hidden="true">3.1.</strong> Configuration</a></li><li class="chapter-item expanded "><a href="../../manual/Usage/SignatureManagement.html"><strong aria-hidden="true">3.2.</strong> Updating Signature Databases</a></li><li class="chapter-item expanded "><a href="../../manual/Usage/Scanning.html"><strong aria-hidden="true">3.3.</strong> Scanning</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../../manual/OnAccess.html"><strong aria-hidden="true">3.3.1.</strong> On-Access Scanning</a></li></ol></li><li class="chapter-item expanded "><a href="../../manual/Usage/Services.html"><strong aria-hidden="true">3.4.</strong> Running ClamAV Services</a></li><li class="chapter-item expanded "><a href="../../manual/Usage/ReportABug.html"><strong aria-hidden="true">3.5.</strong> Report a Bug</a></li></ol></li><li class="chapter-item expanded "><a href="../../manual/Signatures.html"><strong aria-hidden="true">4.</strong> Signatures</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../../manual/Signatures/DatabaseInfo.html"><strong aria-hidden="true">4.1.</strong> CVD Info File</a></li><li class="chapter-item expanded "><a href="../../manual/Signatures/DynamicConfig.html"><strong aria-hidden="true">4.2.</strong> Dynamic Configuration Settings</a></li><li class="chapter-item expanded "><a href="../../manual/Signatures/AuthenticodeRules.html"><strong aria-hidden="true">4.3.</strong> Trusted and Revoked EXE Certificates</a></li><li class="chapter-item expanded "><a href="../../manual/Signatures/FileTypeMagic.html"><strong aria-hidden="true">4.4.</strong> File Type Recognition</a></li><li class="chapter-item expanded "><a href="../../manual/Signatures/AllowLists.html"><strong aria-hidden="true">4.5.</strong> Allow Lists</a></li><li class="chapter-item expanded "><a href="../../manual/Signatures/HashSignatures.html"><strong aria-hidden="true">4.6.</strong> Hash-based Signatures</a></li><li class="chapter-item expanded "><a href="../../manual/Signatures/BodySignatureFormat.html"><strong aria-hidden="true">4.7.</strong> Content-based Signature Format</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../../manual/Signatures/LogicalSignatures.html"><strong aria-hidden="true">4.7.1.</strong> Logical Signatures</a></li><li class="chapter-item expanded "><a href="../../manual/Signatures/ExtendedSignatures.html"><strong aria-hidden="true">4.7.2.</strong> Extended Signatures</a></li></ol></li><li class="chapter-item expanded "><a href="../../manual/Signatures/YaraRules.html"><strong aria-hidden="true">4.8.</strong> YARA Rules</a></li><li class="chapter-item expanded "><a href="../../manual/Signatures/PhishSigs.html"><strong aria-hidden="true">4.9.</strong> Phishing Signatures</a></li><li class="chapter-item expanded "><a href="../../manual/Signatures/BytecodeSignatures.html" class="active"><strong aria-hidden="true">4.10.</strong> Bytecode Signatures</a></li><li class="chapter-item expanded "><a href="../../manual/Signatures/ContainerMetadata.html"><strong aria-hidden="true">4.11.</strong> Container Metadata Signatures</a></li><li class="chapter-item expanded "><a href="../../manual/Signatures/EncryptedArchives.html"><strong aria-hidden="true">4.12.</strong> Archive Passwords (experimental)</a></li><li class="chapter-item expanded "><a href="../../manual/Signatures/SignatureNames.html"><strong aria-hidden="true">4.13.</strong> Signature Names</a></li></ol></li><li class="chapter-item expanded "><a href="../../manual/Development.html"><strong aria-hidden="true">5.</strong> For Developers</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../../manual/Development/github-pr-basics.html"><strong aria-hidden="true">5.1.</strong> Pull Request Basics</a></li><li class="chapter-item expanded "><a href="../../manual/Development/clamav-git-work-flow.html"><strong aria-hidden="true">5.2.</strong> ClamAV Git Work Flow</a></li><li class="chapter-item expanded "><a href="../../manual/Development/personal-forks.html"><strong aria-hidden="true">5.3.</strong> Working with Your Fork</a></li><li class="chapter-item expanded "><a href="../../manual/Development/testing-pull-requests.html"><strong aria-hidden="true">5.4.</strong> Reviewing Pull Requests</a></li><li class="chapter-item expanded "><a href="../../manual/Development/development-builds.html"><strong aria-hidden="true">5.5.</strong> Building for Development</a></li><li class="chapter-item expanded "><a href="../../manual/Development/build-installer-packages.html"><strong aria-hidden="true">5.6.</strong> Building the Installer Packages</a></li><li class="chapter-item expanded "><a href="../../manual/Development/tips-and-tricks.html"><strong aria-hidden="true">5.7.</strong> Dev Tips & Tricks</a></li><li class="chapter-item expanded "><a href="../../manual/Development/performance-profiling.html"><strong aria-hidden="true">5.8.</strong> Performance Profiling</a></li><li class="chapter-item expanded "><a href="../../manual/Development/code-coverage.html"><strong aria-hidden="true">5.9.</strong> Computing Code Coverage</a></li><li class="chapter-item expanded "><a href="../../manual/Development/fuzzing-sanitizers.html"><strong aria-hidden="true">5.10.</strong> Fuzzing Sanitizers</a></li><li class="chapter-item expanded "><a href="../../manual/Development/libclamav.html"><strong aria-hidden="true">5.11.</strong> libclamav</a></li><li class="chapter-item expanded "><a href="../../manual/Development/Contribute.html"><strong aria-hidden="true">5.12.</strong> Contribute</a></li></ol></li><li class="chapter-item expanded "><a href="../../faq/faq.html"><strong aria-hidden="true">6.</strong> Frequently Asked Questions</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../../faq/faq-whichversion.html"><strong aria-hidden="true">6.1.</strong> Selecting the Right Version of ClamAV for You</a></li><li class="chapter-item expanded "><a href="../../faq/faq-freshclam.html"><strong aria-hidden="true">6.2.</strong> FreshClam (Signature Updater)</a></li><li class="chapter-item expanded "><a href="../../faq/faq-cvd.html"><strong aria-hidden="true">6.3.</strong> Signature Database (CVD)</a></li><li class="chapter-item expanded "><a href="../../faq/faq-misc.html"><strong aria-hidden="true">6.4.</strong> Misc</a></li><li class="chapter-item expanded "><a href="../../faq/faq-ml.html"><strong aria-hidden="true">6.5.</strong> Mailing Lists</a></li><li class="chapter-item expanded "><a href="../../faq/faq-safebrowsing.html"><strong aria-hidden="true">6.6.</strong> Safe Browsing</a></li><li class="chapter-item expanded "><a href="../../faq/faq-troubleshoot.html"><strong aria-hidden="true">6.7.</strong> Troubleshooting</a></li><li class="chapter-item expanded "><a href="../../faq/faq-scan-alerts.html"><strong aria-hidden="true">6.8.</strong> Interpreting Scan Alerts</a></li><li class="chapter-item expanded "><a href="../../faq/faq-upgrade.html"><strong aria-hidden="true">6.9.</strong> Upgrading</a></li><li class="chapter-item expanded "><a href="../../faq/faq-rust.html"><strong aria-hidden="true">6.10.</strong> Rust</a></li><li class="chapter-item expanded "><a href="../../faq/faq-win32.html"><strong aria-hidden="true">6.11.</strong> Win32</a></li><li class="chapter-item expanded "><a href="../../faq/faq-pua.html"><strong aria-hidden="true">6.12.</strong> PUA (Potentially Unwanted Application)</a></li><li class="chapter-item expanded "><a href="../../faq/faq-ignore.html"><strong aria-hidden="true">6.13.</strong> Ignore</a></li><li class="chapter-item expanded "><a href="../../faq/faq-uninstall.html"><strong aria-hidden="true">6.14.</strong> Uninstall</a></li><li class="chapter-item expanded "><a href="../../faq/faq-eol.html"><strong aria-hidden="true">6.15.</strong> ClamAV EOL Policy</a></li><li class="spacer"></li></ol></li><li class="chapter-item expanded "><a href="../../community_resources/CommunityResources.html"><strong aria-hidden="true">7.</strong> Community Resources</a></li><li class="spacer"></li><li class="chapter-item expanded "><a href="../../appendix/Appendix.html"><strong aria-hidden="true">8.</strong> Appendix</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../../appendix/Terminology.html"><strong aria-hidden="true">8.1.</strong> Terminology</a></li><li class="chapter-item expanded "><a href="../../appendix/CvdPrivateMirror.html"><strong aria-hidden="true">8.2.</strong> Hosting a Private Database Mirror</a></li><li class="chapter-item expanded "><a href="../../appendix/Authenticode.html"><strong aria-hidden="true">8.3.</strong> Microsoft Authenticode Signature Verification</a></li><li class="chapter-item expanded "><a href="../../appendix/FileTypes.html"><strong aria-hidden="true">8.4.</strong> ClamAV File Types and Target Types</a></li><li class="chapter-item expanded "><a href="../../appendix/FunctionalityLevels.html"><strong aria-hidden="true">8.5.</strong> ClamAV Versions and Functionality Levels</a></li></ol></li></ol>
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<h1 class="menu-title">ClamAV Documentation</h1>
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<h1 id="bytecode-signatures"><a class="header" href="#bytecode-signatures">Bytecode Signatures</a></h1>
<p>Bytecode Signatures are the means by which more complex matching can be performed by writing C code to parse sample content at various stages in file extraction.</p>
<p>It is less complicated than it sounds. Essentially the signature author writes a function in C is compiled down to an intermediate language called "bytecode". This bytecode is encoded in ASCII <code>.cbc</code> file and distributed in <code>bytecode.[cvd|cld]</code>. When the database is loaded, ClamAV can interpret this bytecode to execute the function.</p>
<p>Bytecode functions are provided with a set of APIs that may be used to access the sample data, and to access what metadata ClamAV already has concerning the sample.</p>
<p>The function may at any time call an API to flag the sample as malicious, and may provide the signature/virus name at that time. This means a single bytecode signature (function) is written to handle a given file type and may trigger different alerts with different signature names as additional malicious characteristics for the file type are identified. That isn't to say that only one bytecode signature may be assigned to a given filetype, but that a single author may find it to be more efficient to use a bytecode signature to identify more than one type of malware.</p>
<p>The specifics on how to write and compile bytecode signatures are outside of the scope of this documentation. Extensive documentation on ClamAV Bytecode Signatures are provided with the <a href="https://github.com/Cisco-Talos/clamav-bytecode-compiler">ClamAV Bytecode Compiler</a>.</p>
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