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The policy is open by default. This affords maximum utility for ImageMagick installations that run in a sandboxed environment, perhaps in a Docker instance, or behind a firewall where security risks are greatly diminished as opposed to a public website.</p> 94 95<p>Security is a trade-off between a secure environment and convenience. If you want ImageMagick to be optimally secure, you could, for example, limit ImageMagick to only read or write web safe images (e.g. GIF, JPEG, PNG). However, ImageMagick provides for a more secure option by adjusting the security policy per the requirements of your local environment or organizational policies. The security policy covers areas such as memory, which paths to read or write, how many images are permitted in an image sequence, how long a workflow can run, how much disk the image pixels can consume, a secret passphrase for remote connections, which coders are permitted or denied, and others. These policies should provide robust coverage to not only secure your environment per your requirements but also ensure ImageMagick remains a good citizen (e.g. prevent thrashing with large images) in your local environment.</p> 96 97<p>As an example, suppose you download an image from the internet and unbeknownst to you its been crafted to generate a 20000 by 20000 pixel image. ImageMagick attempts to allocate enough resources (memory, disk) and your system will likely deny the resource request and exit. However, its also possible that your computer might be temporarily sluggish or unavailable or ImageMagick may abort. To prevent such a scenario, you can set limits in the <code>policy.xml</code> configuration file. You might wonder why ImageMagick does not already include reasonable limits? Simply because what is reasonable in your environment, might not be reasonable to someone else. For example, you may have ImageMagick sandboxed where security is not a concern, whereas another user may use ImageMagick to process images on their publically accessible website. Or ImageMagick runs on a host with 1TB of memory whereas another ImageMagick instance runs on an iPhone. By policy, permitting giga-pixel image processing on the large memory host makes sense, not so much for the resource constrained iPhone. If you utilize ImageMagick from a public website, you may want to increase security by preventing usage of the MVG or HTTPS coders. Only you can decide what are reasonable limits taking in consideration your environment. We provide this policy with reasonable limits and encourage you to modify it to suit your local environment:</p> 98 99<pre class="pre-scrollable"><code><policymap> 100 <!-- temporary path must be a preexisting writable directory --> 101 <policy domain="resource" name="temporary-path" value="/tmp"/> 102 <policy domain="resource" name="memory" value="256MiB"/> 103 <policy domain="resource" name="map" value="512MiB"/> 104 <policy domain="resource" name="width" value="8KP"/> 105 <policy domain="resource" name="height" value="8KP"/> 106 <policy domain="resource" name="area" value="16KP"/> 107 <policy domain="resource" name="disk" value="1GiB"/> 108 <policy domain="resource" name="file" value="768"/> 109 <policy domain="resource" name="thread" value="2"/> 110 <policy domain="resource" name="throttle" value="0"/> 111 <policy domain="resource" name="time" value="120"/> 112 <policy domain="resource" name="list-length" value="128"/> 113 <policy domain="system" name="precision" value="6"/> 114 <policy domain="cache" name="shared-secret" stealth="true" value="replace with your secret phrase"/> 115 <policy domain="coder" rights="none" pattern="MVG" /> 116 <policy domain="coder" rights="none" pattern="EPS" /> 117 <policy domain="coder" rights="none" pattern="PS" /> 118 <policy domain="coder" rights="none" pattern="PS2" /> 119 <policy domain="coder" rights="none" pattern="PS3" /> 120 <policy domain="coder" rights="none" pattern="PDF" /> 121 <policy domain="coder" rights="none" pattern="XPS" /> 122 <policy domain="filter" rights="none" pattern="*" /> 123 <policy domain="delegate" rights="none" pattern="HTTPS" /> <!-- prevent 'curl' program from reading HTTPS URL's --> 124 <policy domain="delegate" rights="none" pattern="SHOW" /> 125 <policy domain="delegate" rights="none" pattern="WIN" /> 126 <policy domain="path" rights="none" pattern="@*"/> <!-- indirect reads not permitted --> 127</policymap></code></pre> 128 129<p>Since we process multiple simultaneous sessions, we do not want any one session consuming all the available memory. With this policy, large images are cached to disk. If the image is too large and exceeds the pixel cache disk limit, the program exits. In addition, we place a time limit to prevent any run-away processing tasks. If any one image has a width or height that exceeds 8192 pixels or if an image sequence exceeds 128 frames, an exception is thrown and processing stops. As of ImageMagick 7.0.1-8 and 6.9.4-6, you can prevent the use of any delegate or all delegates (set the pattern to "*"). Note, prior to these releases, use a domain of <code>coder</code> to prevent delegate usage (e.g. <code>domain="coder" rights="none" pattern="HTTPS"</code>). We prevent users from executing any image filters. The policy also prevents indirect reads. If you want to, for example, read text from a file (e.g. <code>caption:@myCaption.txt</code>), you'll need to disable the <code>path</code> policy.</p> 130 131<p>Policy patterns are <em>case sensitive</em>. To get expected behavior, coders and modules must be upper-case (e.g. "EPS" not "eps").</p> 132 133<p>Here is what you can expect when you restrict the HTTPS coder, for example:</p> 134 135<pre class="highlight">-> convert ../images/wizard.png wizard.jpg 136convert: attempt to perform an operation not allowed by the security policy `HTTPS' 137convert: unable to open file: No such file or directory 138convert: no images defined `wizard.jpg'</pre> 139 140<p>As of ImageMagick version 7.0.4-7, you can conveniently deny access to all delegates and coders except for a small subset of proven web-safe image types. For example,</p> 141 142<pre class="highlight"><code><policy domain="delegate" rights="none" pattern="*" /> 143<policy domain="module" rights="none" pattern="*" /> 144<policy domain="module" rights="read | write" pattern="{GIF,JPEG,PNG,WEBP}" /></code></pre> 145 146<p>Here we disable just a few Postscript related formats:</p> 147<pre class="highlight"><code><policy domain="module" rights="none" pattern="{PDF,PS,PS2,PS3,XPS}" /></code></pre> 148 149<p>As of ImageMagick 7.0.7-0, you can allocate the pixel cache and some internal buffers with anonymous memory mapping rather than from heap. As a consequence, the pixels are initialized to zero. You can also securely delete any temporary files for increased security. The value is the number of times to shred (replace its content with random data) before deleting a temporary file. For example,</p> 150<pre class="highlight"><code><policy domain="system" name="memory-map" value="anonymous"/> 151<policy domain="cache" name="memory-map" value="anonymous"/> 152<policy domain="system" name="shred" value="1"/></code></pre> 153 154<p>Some image processing algorithms (e.g. wavelet transform) might consume a substantial amount of memory to complete. ImageMagick maintains a separate memory pool for these large resource requests and as of 7.0.6-1 permits you to set a maximum request limit. If the limit is exceeded, the allocation is instead memory-mapped on disk. Here we limit the maximum memory request by policy:</p> 155<pre class="highlight"><code><policy domain="system" name="max-memory-request" value="256MiB"/> </code></pre> 156 157<p>As of ImageMagick version 7.0.4-23, you can limit the maximum number of images in a sequence. For example, to limit an image sequence to 64 frames, use:</p> 158<pre class="highlight"><code><policy domain="resource" name="list-length" value="64"/></code></pre> 159 160<p>You can verify your policy changes are in effect with this command:</p> 161 162<pre class="pre-scrollable">-> identify -list policy 163Path: ImageMagick/policy.xml 164 Policy: Resource 165 name: time 166 value: 120 167 Policy: Resource 168 name: throttle 169 value: 0 170 Policy: Resource 171 name: thread 172 value: 2 173 Policy: Resource 174 name: file 175 value: 768 176 Policy: Resource 177 name: disk 178 value: 1GiB 179 Policy: Resource 180 name: map 181 value: 512MiB 182 Policy: Resource 183 name: memory 184 value: 256MiB 185 Policy: Resource 186 name: area 187 value: 16KP 188 Policy: Resource 189 name: height 190 value: 8KP 191 Policy: Resource 192 name: width 193 value: 8KP 194 Policy: Resource 195 name: temporary-path 196 value: /tmp 197 Policy: System 198 name: precision 199 value: 6 200 Policy: Path 201 rights: None 202 pattern: @* 203 204Path: [built-in] 205 Policy: Undefined 206 rights: None</pre> 207<p>Notice the <code>Cache</code> policy is not listed due to the <code>stealth</code> property.</p> 208 209<p>As of ImageMagick 7.0.6-0, you can programmatically set the ImageMagick security policy with SetMagickSecurityPolicy() (MagickCore) or MagickSetSecurityPolicy() (MagickWand).</p> 210 211<p>As of ImageMagick version 7.0.8-11, you can set a module security policy. For example, to prevent Postscript or PDF interpretation, use:</p> 212<pre class="highlight"><code><policy domain="module" rights="none" pattern="{ps,pdf,xps}/></code></pre> 213 214<p>For additional details about resource limits and the policy configuration file, read <a href="resources.html">Resources</a> and <a href="architecture.html">Architecture</a>.</p> 215 216<h2><a class="anchor" id="synchronize"></a>Pixel Cache Synchronize Policy</h2> 217 218<p>When writing image pixels to disk, ImageMagick firsts preallocates the disk file, which is much faster than fully populating the file with zeros. To further increase performance, we memory-map the file on disk. With memory-mapping, we get an increase in performance (up to 5x), however, there remains a possibility that as the disk file is populated, it may run out of free space. The OS then throws a SIGBUS signal which prevents ImageMagick from continuing. To prevent a SIGBUS, use this security policy: 219 220<pre class="highlight"> 221<policy domain="cache" name="synchronize" value="True"/> 222</pre> 223 224<p>Set to True to ensure all image data is fully flushed and synchronized to disk. There is a performance penalty, however, the benefits include ensuring a valid image file in the event of a system crash and early reporting if there is not enough disk space for the image pixel cache.</p> 225 226<h2><a class="anchor" id="zero-configuration"></a>Zero Configuration Security Policy</h2> 227 228<p>A zero configuration build of ImageMagick does not permit external configuration files. To define your security policy, you must instead edit the <code>MagickCore/policy-private.h</code> source module, add your policy statements, and then build the ImageMagick distribution. Here is an example zero configuration security policy:</p> 229 230<pre class="highlight"><code>static const char 231 *ZeroConfigurationPolicy = \ 232"<policymap> \ 233 <policy domain=\"coder\" rights=\"none\" pattern=\"MVG\"/> \ 234</policymap>";</code></pre> 235 236<h2><a class="anchor" id="other"></a>Other Security Considerations</h2> 237 238<p>If you spot a security flaw in ImageMagick, post your concern as an issue to 239<a href="https://github.com/ImageMagick/ImageMagick/issues">GitHub</a>. Be sure to include how to reproduce the security flaw and a link to any images needed to reproduce the flaw. Alternatively, <a href="https://imagemagick.org/script/contact.php">contact us</a> and select Security Issue as the issue.</p> 240 241<p>In addition to the security policy, you can make ImageMagick safer by ...</p> 242<ul> 243<li>keeping ImageMagick up-to-date. The latest releases have fixes for any security flaws we discovered in the past;</li> 244<li>sanitizing any filenames or command line options you pass to ImageMagick;</li> 245<li>running ImageMagick in a sanitized software container such as Docker;</li> 246<li>running ImageMagick as the least-privileged user (e.g. 'nobody');</li> 247<li>explicitly setting the image file type. For example, use the filename <code>png:image.png</code> rather than <code>image.png</code>. Without an explicit image type in the filename, ImageMagick guesses the image type.</li> 248</ul> 249 250</div> 251 </div> 252 </main><!-- /.container --> 253 <footer class="magick-footer"> 254 <p><a href="security-policy.html">Security</a> • 255 <a href="architecture.html">Architecture</a> 256 257 <a href="security-policy.html#"><img class="d-inline" id="wand" alt="And Now a Touch of Magick" width="16" height="16" src="../images/wand.ico"/></a> 258 259 <a href="links.html">Related</a> • 260 <a href="sitemap.html">Sitemap</a> 261 <br/> 262 <a href="support.html">Donate</a> • 263 <a href="http://pgp.mit.edu/pks/lookup?op=get&search=0x89AB63D48277377A">Public Key</a> • 264 <a href="https://imagemagick.org/script/contact.php">Contact Us</a> 265 <br/> 266 <small>© 1999-2020 ImageMagick Studio LLC</small></p> 267 </footer> 268 269 <!-- Javascript assets --> 270 <script src="assets/magick.js" crossorigin="anonymous"></script> 271 <script>window.jQuery || document.write('<script src="https://localhost/ajax/libs/jquery/3.4.1/jquery.min.js"><\/script>')</script> 272</body> 273</html> 274<!-- Magick Cache 5th January 2020 11:35 -->
