MINI MINI MANI MO
<!DOCTYPE HTML>
<html lang="en" class="sidebar-visible no-js clamav">
<head>
<!-- Book generated using mdBook -->
<meta charset="UTF-8">
<title>Content-based Signature Format - ClamAV Documentation</title>
<!-- Custom HTML head -->
<meta content="text/html; charset=utf-8" http-equiv="Content-Type">
<meta name="description" content="An open source malware detection toolkit and antivirus engine.">
<meta name="viewport" content="width=device-width, initial-scale=1">
<meta name="theme-color" content="#ffffff" />
<link rel="shortcut icon" href="../../favicon.png">
<link rel="stylesheet" href="../../css/variables.css">
<link rel="stylesheet" href="../../css/general.css">
<link rel="stylesheet" href="../../css/chrome.css">
<link rel="stylesheet" href="../../css/print.css" media="print">
<!-- Fonts -->
<link rel="stylesheet" href="../../FontAwesome/css/font-awesome.css">
<link rel="stylesheet" href="../../fonts/fonts.css">
<!-- Highlight.js Stylesheets -->
<link rel="stylesheet" href="../../highlight.css">
<link rel="stylesheet" href="../../tomorrow-night.css">
<link rel="stylesheet" href="../../ayu-highlight.css">
<!-- Custom theme stylesheets -->
<!-- MathJax -->
<script async type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.1/MathJax.js?config=TeX-AMS-MML_HTMLorMML"></script>
</head>
<body>
<!-- Provide site root to javascript -->
<script type="text/javascript">
var path_to_root = "../../";
var default_theme = window.matchMedia("(prefers-color-scheme: dark)").matches ? "clamav" : "clamav";
</script>
<!-- Work around some values being stored in localStorage wrapped in quotes -->
<script type="text/javascript">
try {
var theme = localStorage.getItem('mdbook-theme');
var sidebar = localStorage.getItem('mdbook-sidebar');
if (theme.startsWith('"') && theme.endsWith('"')) {
localStorage.setItem('mdbook-theme', theme.slice(1, theme.length - 1));
}
if (sidebar.startsWith('"') && sidebar.endsWith('"')) {
localStorage.setItem('mdbook-sidebar', sidebar.slice(1, sidebar.length - 1));
}
} catch (e) { }
</script>
<!-- Set the theme before any content is loaded, prevents flash -->
<script type="text/javascript">
var theme;
try { theme = localStorage.getItem('mdbook-theme'); } catch(e) { }
if (theme === null || theme === undefined) { theme = default_theme; }
var html = document.querySelector('html');
html.classList.remove('no-js')
html.classList.remove('clamav')
html.classList.add(theme);
html.classList.add('js');
</script>
<!-- Hide / unhide sidebar before it is displayed -->
<script type="text/javascript">
var html = document.querySelector('html');
var sidebar = 'hidden';
if (document.body.clientWidth >= 1080) {
try { sidebar = localStorage.getItem('mdbook-sidebar'); } catch(e) { }
sidebar = sidebar || 'visible';
}
html.classList.remove('sidebar-visible');
html.classList.add("sidebar-" + sidebar);
</script>
<nav id="sidebar" class="sidebar" aria-label="Table of contents">
<div class="sidebar-scrollbox">
<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" class="active"><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"><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>
</div>
<div id="sidebar-resize-handle" class="sidebar-resize-handle"></div>
</nav>
<div id="page-wrapper" class="page-wrapper">
<div class="page">
<div id="menu-bar-hover-placeholder"></div>
<div id="menu-bar" class="menu-bar sticky bordered">
<div class="left-buttons">
<button id="sidebar-toggle" class="icon-button" type="button" title="Toggle Table of Contents" aria-label="Toggle Table of Contents" aria-controls="sidebar">
<i class="fa fa-bars"></i>
</button>
<button id="theme-toggle" class="icon-button" type="button" title="Change theme" aria-label="Change theme" aria-haspopup="true" aria-expanded="false" aria-controls="theme-list">
<i class="fa fa-paint-brush"></i>
</button>
<ul id="theme-list" class="theme-popup" aria-label="Themes" role="menu">
<li role="none"><button role="menuitem" class="theme" id="clamav">Dark</button></li>
<li role="none"><button role="menuitem" class="theme" id="clamav_light">Light</button></li>
</ul>
<button id="search-toggle" class="icon-button" type="button" title="Search. (Shortkey: s)" aria-label="Toggle Searchbar" aria-expanded="false" aria-keyshortcuts="S" aria-controls="searchbar">
<i class="fa fa-search"></i>
</button>
</div>
<h1 class="menu-title">ClamAV Documentation</h1>
<div class="right-buttons">
<a href="../../print.html" title="Print this book" aria-label="Print this book">
<i id="print-button" class="fa fa-print"></i>
</a>
</div>
</div>
<div id="search-wrapper" class="hidden">
<form id="searchbar-outer" class="searchbar-outer">
<input type="search" name="search" id="searchbar" name="searchbar" placeholder="Search this book ..." aria-controls="searchresults-outer" aria-describedby="searchresults-header">
</form>
<div id="searchresults-outer" class="searchresults-outer hidden">
<div id="searchresults-header" class="searchresults-header"></div>
<ul id="searchresults">
</ul>
</div>
</div>
<!-- Apply ARIA attributes after the sidebar and the sidebar toggle button are added to the DOM -->
<script type="text/javascript">
document.getElementById('sidebar-toggle').setAttribute('aria-expanded', sidebar === 'visible');
document.getElementById('sidebar').setAttribute('aria-hidden', sidebar !== 'visible');
Array.from(document.querySelectorAll('#sidebar a')).forEach(function(link) {
link.setAttribute('tabIndex', sidebar === 'visible' ? 0 : -1);
});
</script>
<div id="content" class="content">
<main>
<h1 id="body-based-signature-content-format"><a class="header" href="#body-based-signature-content-format">Body-based Signature Content Format</a></h1>
<p>ClamAV stores all body-based (content-based) signatures in a hexadecimal format, with exception to ClamAV's YARA rule support. In this section by a hex-signature we mean a fragment of malware’s body converted into a hexadecimal string which can be additionally extended using various wildcards.</p>
<h2 id="hexadecimal-format"><a class="header" href="#hexadecimal-format">Hexadecimal format</a></h2>
<p>You can use <code>sigtool --hex-dump</code> to convert any data into a hex-string:</p>
<pre><code class="language-bash">zolw@localhost:/tmp/test$ sigtool --hex-dump
How do I look in hex?
486f7720646f2049206c6f6f6b20696e206865783f0a
</code></pre>
<h2 id="wildcards"><a class="header" href="#wildcards">Wildcards</a></h2>
<p>ClamAV supports the following wildcards for hex-signatures:</p>
<ul>
<li>
<p><code>??</code></p>
<p>Match any byte.</p>
</li>
<li>
<p><code>a?</code></p>
<p>Match a high nibble (the four high bits).</p>
</li>
<li>
<p><code>?a</code></p>
<p>Match a low nibble (the four low bits).</p>
</li>
<li>
<p><code>*</code></p>
<p>Match any number of bytes.</p>
</li>
<li>
<p><code>{n}</code></p>
<p>Match <code>n</code> bytes.</p>
</li>
<li>
<p><code>{-n}</code></p>
<p>Match <code>n</code> or less bytes.</p>
</li>
<li>
<p><code>{n-}</code></p>
<p>Match <code>n</code> or more bytes.</p>
</li>
<li>
<p><code>{n-m}</code></p>
<p>Match between <code>n</code> and <code>m</code> bytes (where <code>m > n</code>).</p>
</li>
<li>
<p><code>HEXSIG[x-y]aa</code> or <code>aa[x-y]HEXSIG</code></p>
<p>Match <code>aa</code> anchored to a hex-signature, see <a href="https://bugzilla.clamav.net/show_bug.cgi?id=776">Bugzilla ticket 776</a> for discussion and
examples.</p>
</li>
</ul>
<p>The range signatures <code>*</code> and <code>{}</code> virtually separate a hex-signature into two parts, eg. <code>aabbcc*bbaacc</code> is treated as two sub-signatures <code>aabbcc</code> and <code>bbaacc</code> with any number of bytes between them. It’s a requirement that each sub-signature includes a block of two static characters somewhere in its body. Note that there is one exception to this restriction; that is when the range wildcard is of the form <code>{n}</code> with <code>n<128</code>. In this case, ClamAV uses an optimization and translates <code>{n}</code> to the string consisting of <code>n ??</code> character wildcards. Character wildcards do not divide hex signatures into two parts and so the two static character requirement does not apply.</p>
<h2 id="character-classes"><a class="header" href="#character-classes">Character classes</a></h2>
<p>ClamAV supports the following character classes for hex-signatures:</p>
<ul>
<li>
<p><code>(B)</code></p>
<p>Match word boundary (including file boundaries).</p>
</li>
<li>
<p><code>(L)</code></p>
<p>Match CR, CRLF or file boundaries.</p>
</li>
<li>
<p><code>(W)</code></p>
<p>Match a non-alphanumeric character.</p>
</li>
</ul>
<h2 id="alternate-strings"><a class="header" href="#alternate-strings">Alternate strings</a></h2>
<ul>
<li>
<p>Single-byte alternates (clamav-0.96) <code>(aa|bb|cc|...)</code> or <code>!(aa|bb|cc|...)</code> Match a member from a set of bytes (eg: <code>aa</code>, <code>bb</code>, <code>cc</code>, ...).</p>
<ul>
<li>Negation operation can be applied to match any non-member, assumed to be one-byte in length.</li>
<li>Signature modifiers and wildcards cannot be applied.</li>
</ul>
</li>
<li>
<p>Multi-byte fixed length alternates <code>(aaaa|bbbb|cccc|...)</code> or <code>!(aaaa|bbbb|cccc|...)</code> Match a member from a set of multi-byte alternates (eg: aaaa, bbbb, cccc, ...) of n-length.</p>
<ul>
<li>All set members must be the same length.</li>
<li>Negation operation can be applied to match any non-member, assumed to be n-bytes in length (clamav-0.98.2).</li>
<li>Signature modifiers and wildcards cannot be applied.</li>
</ul>
</li>
<li>
<p>Generic alternates (clamav-0.99) <code>(alt1|alt2|alt3|...)</code> Match a member from a set of alternates (eg: alt1, alt2, alt3, ...) that can be of variable lengths.</p>
<ul>
<li>Negation operation cannot be applied.</li>
<li>Signature modifiers and nibble wildcards (eg: <code>??, a?, ?a</code>) can be applied.</li>
<li>Ranged wildcards (eg: <code>{n-m}</code>) are limited to a fixed range of less than 128 bytes (eg: <code>{1} -> {127}</code>).</li>
</ul>
</li>
</ul>
<blockquote>
<p><em>Note</em>: Using signature modifiers and wildcards classifies the alternate type to be a generic alternate. Thus single-byte alternates and multi-byte fixed length alternates can use signature modifiers and wildcards but will be classified as generic alternate. This means that negation cannot be applied in this situation and there is a slight performance impact.</p>
</blockquote>
</main>
<nav class="nav-wrapper" aria-label="Page navigation">
<!-- Mobile navigation buttons -->
<a rel="prev" href="../../manual/Signatures/HashSignatures.html" class="mobile-nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
<i class="fa fa-angle-left"></i>
</a>
<a rel="next" href="../../manual/Signatures/LogicalSignatures.html" class="mobile-nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right">
<i class="fa fa-angle-right"></i>
</a>
<div style="clear: both"></div>
</nav>
</div>
</div>
<nav class="nav-wide-wrapper" aria-label="Page navigation">
<a rel="prev" href="../../manual/Signatures/HashSignatures.html" class="nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
<i class="fa fa-angle-left"></i>
</a>
<a rel="next" href="../../manual/Signatures/LogicalSignatures.html" class="nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right">
<i class="fa fa-angle-right"></i>
</a>
</nav>
</div>
<script type="text/javascript">
window.playground_line_numbers = true;
</script>
<script type="text/javascript">
window.playground_copyable = true;
</script>
<script src="../../ace.js" type="text/javascript" charset="utf-8"></script>
<script src="../../editor.js" type="text/javascript" charset="utf-8"></script>
<script src="../../mode-rust.js" type="text/javascript" charset="utf-8"></script>
<script src="../../theme-dawn.js" type="text/javascript" charset="utf-8"></script>
<script src="../../theme-tomorrow_night.js" type="text/javascript" charset="utf-8"></script>
<script src="../../elasticlunr.min.js" type="text/javascript" charset="utf-8"></script>
<script src="../../mark.min.js" type="text/javascript" charset="utf-8"></script>
<script src="../../searcher.js" type="text/javascript" charset="utf-8"></script>
<script src="../../clipboard.min.js" type="text/javascript" charset="utf-8"></script>
<script src="../../highlight.js" type="text/javascript" charset="utf-8"></script>
<script src="../../book.js" type="text/javascript" charset="utf-8"></script>
<!-- Custom JS scripts -->
</body>
</html>
OHA YOOOO