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csaw-ctf-2013-web300-writeup.html
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<h1 class="entry-title"><a href="https://kingx.me/csaw-ctf-2013-web300-writeup.html" rel="bookmark" title="CSAW CTF 2013 Web300 Writeup">CSAW CTF 2013 Web300 Writeup</a></h1>
<h2><span class="entry-date date published"><time datetime="2013-09-24T00:00:00-04:00">September 24, 2013, KINGX</time></span></h2>
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<span class="entry-tags" style="color:red;font-size:13px;margin-bottom: 0px;">「声明：本博客中涉及到的相关漏洞均为官方已经公开并修复的漏洞，涉及到的安全技术也仅用于企业安全建设和安全对抗研究。本文仅限业内技术研究与讨论，严禁用于非法用途，否则产生的一切后果自行承担。」</span>
<p>面向全球的入门级CSAW CTF 2013比赛已经落幕。</p>
<p>中秋时跟Tony组队玩了一下。感觉好多<code class="highlighter-rouge">reverse</code>和<code class="highlighter-rouge">exploit</code>的题目，苦手啊。
这里对其中Web类的300分题目作一个小结。
题目内容是一个apk应用，运行如下图：</p>
<p><img src="https://kingx.me/images/articles/201309/0.jpg" alt="apk" /></p>
<p>很简单的一个应用，貌似只有一个简单的登录功能。通过查看资源文件，发现了url地址：<a href="https://webchal.isis.poly.edu/csaw.php">https://webchal.isis.poly.edu/csaw.php</a></p>
<p>目测就是向这个地址提交登录数据。使用dex2jar反编译该apk,代码没有经过混淆，但是登录的关键类AuthRequest的主要方法无法编译出源码。</p>
<p>于是打开burpsuit，配置模拟器代理，想抓包分析一下登录过程。但是发现apk好像会检测ssl证书的真实性，在模拟器上安装了burpsuit的证书仍然不行，会返回<code class="highlighter-rouge">Unknown Error</code>的错误信息。查找反编译出来的源码，发现apk中的有个方法会检查SSL证书：</p>
<figure class="highlight"><pre><code class="language-java" data-lang="java"><span class="kd">private</span> <span class="kd">static</span> <span class="kd">class</span> <span class="nc">AlwaysTrustManager</span>
<span class="kd">implements</span> <span class="n">X509TrustManager</span>
<span class="o">{</span>
<span class="n">String</span> <span class="n">C</span> <span class="o">=</span> <span class="s">"C=US"</span><span class="o">;</span>
<span class="n">String</span> <span class="n">CN1</span> <span class="o">=</span> <span class="s">"CN=ROOT CA"</span><span class="o">;</span>
<span class="n">String</span> <span class="n">CN2</span> <span class="o">=</span> <span class="s">"CN=webchal.isis.poly.edu"</span><span class="o">;</span>
<span class="n">String</span> <span class="n">L</span> <span class="o">=</span> <span class="s">"L=New York"</span><span class="o">;</span>
<span class="n">String</span> <span class="n">O1</span> <span class="o">=</span> <span class="s">"O=Research and Development"</span><span class="o">;</span>
<span class="n">String</span> <span class="n">O2</span> <span class="o">=</span> <span class="s">"O=Clandestine Automations Intl"</span><span class="o">;</span>
<span class="n">String</span> <span class="n">OU</span> <span class="o">=</span> <span class="s">"OU=Black Ops"</span><span class="o">;</span>
<span class="n">BigInteger</span> <span class="n">SERIAL</span> <span class="o">=</span> <span class="k">new</span> <span class="n">BigInteger</span><span class="o">(</span><span class="s">"4919"</span><span class="o">);</span>
<span class="n">String</span> <span class="n">ST</span> <span class="o">=</span> <span class="s">"ST=New York"</span><span class="o">;</span>
<span class="kd">private</span> <span class="n">Boolean</span> <span class="nf">isValid</span><span class="o">(</span><span class="n">String</span><span class="o">[]</span> <span class="n">paramArrayOfString1</span><span class="o">,</span> <span class="n">String</span><span class="o">[]</span> <span class="n">paramArrayOfString2</span><span class="o">,</span> <span class="n">BigInteger</span> <span class="n">paramBigInteger</span><span class="o">)</span>
<span class="o">{</span>
<span class="k">if</span> <span class="o">((</span><span class="n">paramArrayOfString1</span><span class="o">[</span><span class="mi">0</span><span class="o">].</span><span class="na">equals</span><span class="o">(</span><span class="k">this</span><span class="o">.</span><span class="na">CN1</span><span class="o">))</span> <span class="o">&&</span> <span class="o">(</span><span class="n">paramArrayOfString1</span><span class="o">[</span><span class="mi">1</span><span class="o">].</span><span class="na">equals</span><span class="o">(</span><span class="k">this</span><span class="o">.</span><span class="na">OU</span><span class="o">))</span> <span class="o">&&</span> <span class="o">(</span><span class="n">paramArrayOfString1</span><span class="o">[</span><span class="mi">2</span><span class="o">].</span><span class="na">equals</span><span class="o">(</span><span class="k">this</span><span class="o">.</span><span class="na">O1</span><span class="o">))</span> <span class="o">&&</span> <span class="o">(</span><span class="n">paramArrayOfString1</span><span class="o">[</span><span class="mi">3</span><span class="o">].</span><span class="na">equals</span><span class="o">(</span><span class="k">this</span><span class="o">.</span><span class="na">O2</span><span class="o">))</span> <span class="o">&&</span> <span class="o">(</span><span class="n">paramArrayOfString1</span><span class="o">[</span><span class="mi">4</span><span class="o">].</span><span class="na">equals</span><span class="o">(</span><span class="k">this</span><span class="o">.</span><span class="na">L</span><span class="o">))</span> <span class="o">&&</span> <span class="o">(</span><span class="n">paramArrayOfString1</span><span class="o">[</span><span class="mi">5</span><span class="o">].</span><span class="na">equals</span><span class="o">(</span><span class="k">this</span><span class="o">.</span><span class="na">ST</span><span class="o">))</span> <span class="o">&&</span> <span class="o">(</span><span class="n">paramArrayOfString1</span><span class="o">[</span><span class="mi">6</span><span class="o">].</span><span class="na">equals</span><span class="o">(</span><span class="k">this</span><span class="o">.</span><span class="na">C</span><span class="o">))</span> <span class="o">&&</span> <span class="o">(</span><span class="n">paramArrayOfString2</span><span class="o">[</span><span class="mi">0</span><span class="o">].</span><span class="na">equals</span><span class="o">(</span><span class="k">this</span><span class="o">.</span><span class="na">CN2</span><span class="o">))</span> <span class="o">&&</span> <span class="o">(</span><span class="n">paramArrayOfString2</span><span class="o">[</span><span class="mi">1</span><span class="o">].</span><span class="na">equals</span><span class="o">(</span><span class="k">this</span><span class="o">.</span><span class="na">OU</span><span class="o">))</span> <span class="o">&&</span> <span class="o">(</span><span class="n">paramArrayOfString2</span><span class="o">[</span><span class="mi">2</span><span class="o">].</span><span class="na">equals</span><span class="o">(</span><span class="k">this</span><span class="o">.</span><span class="na">O1</span><span class="o">))</span> <span class="o">&&</span> <span class="o">(</span><span class="n">paramArrayOfString2</span><span class="o">[</span><span class="mi">3</span><span class="o">].</span><span class="na">equals</span><span class="o">(</span><span class="k">this</span><span class="o">.</span><span class="na">O2</span><span class="o">))</span> <span class="o">&&</span> <span class="o">(</span><span class="n">paramArrayOfString2</span><span class="o">[</span><span class="mi">4</span><span class="o">].</span><span class="na">equals</span><span class="o">(</span><span class="k">this</span><span class="o">.</span><span class="na">ST</span><span class="o">))</span> <span class="o">&&</span> <span class="o">(</span><span class="n">paramArrayOfString2</span><span class="o">[</span><span class="mi">5</span><span class="o">].</span><span class="na">equals</span><span class="o">(</span><span class="k">this</span><span class="o">.</span><span class="na">C</span><span class="o">))</span> <span class="o">&&</span> <span class="o">(</span><span class="n">paramBigInteger</span><span class="o">.</span><span class="na">equals</span><span class="o">(</span><span class="k">this</span><span class="o">.</span><span class="na">SERIAL</span><span class="o">)))</span>
<span class="k">return</span> <span class="n">Boolean</span><span class="o">.</span><span class="na">valueOf</span><span class="o">(</span><span class="kc">true</span><span class="o">);</span>
<span class="k">return</span> <span class="n">Boolean</span><span class="o">.</span><span class="na">valueOf</span><span class="o">(</span><span class="kc">false</span><span class="o">);</span>
<span class="o">}</span></code></pre></figure>
<p>使用apktool反汇编apk,得到smali源码，找到该方法对应的smali代码：</p>
<figure class="highlight"><pre><code class="language-java" data-lang="java"><span class="o">.</span><span class="na">method</span> <span class="kd">private</span> <span class="nf">isValid</span><span class="o">([</span><span class="n">Ljava</span><span class="o">/</span><span class="n">lang</span><span class="o">/</span><span class="n">String</span><span class="o">;[</span><span class="n">Ljava</span><span class="o">/</span><span class="n">lang</span><span class="o">/</span><span class="n">String</span><span class="o">;</span><span class="n">Ljava</span><span class="o">/</span><span class="n">math</span><span class="o">/</span><span class="n">BigInteger</span><span class="o">;)</span><span class="n">Ljava</span><span class="o">/</span><span class="n">lang</span><span class="o">/</span><span class="n">Boolean</span><span class="o">;</span>
<span class="o">.</span><span class="na">locals</span> <span class="mi">7</span>
<span class="o">.</span><span class="na">parameter</span> <span class="s">"issuerDN"</span>
<span class="o">.</span><span class="na">parameter</span> <span class="s">"subjectDN"</span>
<span class="o">.</span><span class="na">parameter</span> <span class="s">"serial"</span>
<span class="o">.</span><span class="na">prologue</span>
<span class="kd">const</span><span class="o">/</span><span class="mi">4</span> <span class="n">v6</span><span class="o">,</span> <span class="mh">0x4</span>
<span class="kd">const</span><span class="o">/</span><span class="mi">4</span> <span class="n">v5</span><span class="o">,</span> <span class="mh">0x3</span>
<span class="kd">const</span><span class="o">/</span><span class="mi">4</span> <span class="n">v4</span><span class="o">,</span> <span class="mh">0x2</span>
<span class="kd">const</span><span class="o">/</span><span class="mi">4</span> <span class="n">v3</span><span class="o">,</span> <span class="mh">0x1</span>
<span class="kd">const</span><span class="o">/</span><span class="mi">4</span> <span class="n">v2</span><span class="o">,</span> <span class="mh">0x0</span>
<span class="o">.</span><span class="na">line</span> <span class="mi">103</span>
<span class="n">aget</span><span class="o">-</span><span class="n">object</span> <span class="n">v0</span><span class="o">,</span> <span class="n">p1</span><span class="o">,</span> <span class="n">v2</span>
<span class="n">iget</span><span class="o">-</span><span class="n">object</span> <span class="n">v1</span><span class="o">,</span> <span class="n">p0</span><span class="o">,</span> <span class="n">Lops</span><span class="o">/</span><span class="n">black</span><span class="o">/</span><span class="n">herpderper</span><span class="o">/</span><span class="n">TrustModifier$AlwaysTrustManager</span><span class="o">;-></span><span class="nl">CN1:</span><span class="n">Ljava</span><span class="o">/</span><span class="n">lang</span><span class="o">/</span><span class="n">String</span><span class="o">;</span>
<span class="n">invoke</span><span class="o">-</span><span class="n">virtual</span> <span class="o">{</span><span class="n">v0</span><span class="o">,</span> <span class="n">v1</span><span class="o">},</span> <span class="n">Ljava</span><span class="o">/</span><span class="n">lang</span><span class="o">/</span><span class="n">String</span><span class="o">;-></span><span class="n">equals</span><span class="o">(</span><span class="n">Ljava</span><span class="o">/</span><span class="n">lang</span><span class="o">/</span><span class="n">Object</span><span class="o">;)</span><span class="n">Z</span>
<span class="n">move</span><span class="o">-</span><span class="n">result</span> <span class="n">v0</span>
<span class="k">if</span><span class="o">-</span><span class="n">eqz</span> <span class="n">v0</span><span class="o">,</span> <span class="o">:</span><span class="n">cond_0</span>
<span class="n">aget</span><span class="o">-</span><span class="n">object</span> <span class="n">v0</span><span class="o">,</span> <span class="n">p1</span><span class="o">,</span> <span class="n">v3</span>
<span class="n">iget</span><span class="o">-</span><span class="n">object</span> <span class="n">v1</span><span class="o">,</span> <span class="n">p0</span><span class="o">,</span> <span class="n">Lops</span><span class="o">/</span><span class="n">black</span><span class="o">/</span><span class="n">herpderper</span><span class="o">/</span><span class="n">TrustModifier$AlwaysTrustManager</span><span class="o">;-></span><span class="nl">OU:</span><span class="n">Ljava</span><span class="o">/</span><span class="n">lang</span><span class="o">/</span><span class="n">String</span><span class="o">;</span>
<span class="n">invoke</span><span class="o">-</span><span class="n">virtual</span> <span class="o">{</span><span class="n">v0</span><span class="o">,</span> <span class="n">v1</span><span class="o">},</span> <span class="n">Ljava</span><span class="o">/</span><span class="n">lang</span><span class="o">/</span><span class="n">String</span><span class="o">;-></span><span class="n">equals</span><span class="o">(</span><span class="n">Ljava</span><span class="o">/</span><span class="n">lang</span><span class="o">/</span><span class="n">Object</span><span class="o">;)</span><span class="n">Z</span>
<span class="n">move</span><span class="o">-</span><span class="n">result</span> <span class="n">v0</span>
<span class="k">if</span><span class="o">-</span><span class="n">eqz</span> <span class="n">v0</span><span class="o">,</span> <span class="o">:</span><span class="n">cond_0</span>
<span class="n">aget</span><span class="o">-</span><span class="n">object</span> <span class="n">v0</span><span class="o">,</span> <span class="n">p1</span><span class="o">,</span> <span class="n">v4</span></code></pre></figure>
<p>与java代码比对，smali代码中，分别将传入的数组中的每个元素与对应的局部变量比较，如果不相等就跳转到:cond_0代码段。</p>
<figure class="highlight"><pre><code class="language-java" data-lang="java"><span class="o">.</span><span class="na">line</span> <span class="mi">119</span>
<span class="n">invoke</span><span class="o">-</span><span class="kd">static</span> <span class="o">{</span><span class="n">v3</span><span class="o">},</span> <span class="n">Ljava</span><span class="o">/</span><span class="n">lang</span><span class="o">/</span><span class="n">Boolean</span><span class="o">;-></span><span class="n">valueOf</span><span class="o">(</span><span class="n">Z</span><span class="o">)</span><span class="n">Ljava</span><span class="o">/</span><span class="n">lang</span><span class="o">/</span><span class="n">Boolean</span><span class="o">;</span>
<span class="n">move</span><span class="o">-</span><span class="n">result</span><span class="o">-</span><span class="n">object</span> <span class="n">v0</span>
<span class="o">.</span><span class="na">line</span> <span class="mi">121</span>
<span class="o">:</span><span class="n">goto_0</span>
<span class="k">return</span><span class="o">-</span><span class="n">object</span> <span class="n">v0</span>
<span class="o">:</span><span class="n">cond_0</span>
<span class="n">invoke</span><span class="o">-</span><span class="kd">static</span> <span class="o">{</span><span class="n">v3</span><span class="o">},</span> <span class="n">Ljava</span><span class="o">/</span><span class="n">lang</span><span class="o">/</span><span class="n">Boolean</span><span class="o">;-></span><span class="n">valueOf</span><span class="o">(</span><span class="n">Z</span><span class="o">)</span><span class="n">Ljava</span><span class="o">/</span><span class="n">lang</span><span class="o">/</span><span class="n">Boolean</span><span class="o">;</span>
<span class="n">move</span><span class="o">-</span><span class="n">result</span><span class="o">-</span><span class="n">object</span> <span class="n">v0</span>
<span class="k">goto</span> <span class="o">:</span><span class="n">goto_0</span>
<span class="o">.</span><span class="na">end</span> <span class="n">method</span></code></pre></figure>
<p>:cond_0代码段就是将v2(也就是false)作为boolean型赋值给v0,然后跳转到:goto_0代码段return v0。如果全部相等则不会跳转直接顺序执行直到:goto_0代码段return v0(此时为true)。这里将:cond_0代码段改为也返回true。即绕过apk中ssl证书的验证。</p>
<p>使用apktool重新构建，autosign给apk签名。使用篡改过的apk登录，可以正常抓包。但是服务端返回Client integrity fault。貌似会检测apk的完整性。查找源代码，登录代码如下：</p>
<figure class="highlight"><pre><code class="language-java" data-lang="java"><span class="kd">public</span> <span class="kd">class</span> <span class="nc">UserLoginTask</span> <span class="kd">extends</span> <span class="n">AsyncTask</span><span class="o"><</span><span class="n">Void</span><span class="o">,</span> <span class="n">Void</span><span class="o">,</span> <span class="n">Boolean</span><span class="o">></span>
<span class="o">{</span>
<span class="kd">public</span> <span class="nf">UserLoginTask</span><span class="o">()</span>
<span class="o">{</span>
<span class="o">}</span>
<span class="kd">protected</span> <span class="n">Boolean</span> <span class="nf">doInBackground</span><span class="o">(</span><span class="n">Void</span><span class="o">[]</span> <span class="n">paramArrayOfVoid</span><span class="o">)</span>
<span class="o">{</span>
<span class="k">try</span>
<span class="o">{</span>
<span class="n">String</span><span class="o">[]</span> <span class="n">arrayOfString</span> <span class="o">=</span> <span class="k">new</span> <span class="n">String</span><span class="o">[</span><span class="mi">4</span><span class="o">];</span>
<span class="n">arrayOfString</span><span class="o">[</span><span class="mi">0</span><span class="o">]</span> <span class="o">=</span> <span class="n">SuperSecretAuthorizationActivity</span><span class="o">.</span><span class="na">this</span><span class="o">.</span><span class="na">getString</span><span class="o">(</span><span class="mi">2130968593</span><span class="o">);</span>
<span class="n">arrayOfString</span><span class="o">[</span><span class="mi">1</span><span class="o">]</span> <span class="o">=</span> <span class="n">SuperSecretAuthorizationActivity</span><span class="o">.</span><span class="na">this</span><span class="o">.</span><span class="na">mEmail</span><span class="o">;</span>
<span class="n">arrayOfString</span><span class="o">[</span><span class="mi">2</span><span class="o">]</span> <span class="o">=</span> <span class="n">SuperSecretAuthorizationActivity</span><span class="o">.</span><span class="na">this</span><span class="o">.</span><span class="na">mPassword</span><span class="o">;</span>
<span class="n">arrayOfString</span><span class="o">[</span><span class="mi">3</span><span class="o">]</span> <span class="o">=</span> <span class="n">SuperSecretAuthorizationActivity</span><span class="o">.</span><span class="na">this</span><span class="o">.</span><span class="na">sigChar</span><span class="o">();</span>
<span class="n">SuperSecretAuthorizationActivity</span><span class="o">.</span><span class="na">this</span><span class="o">.</span><span class="na">authreq</span><span class="o">.</span><span class="na">execute</span><span class="o">(</span><span class="n">arrayOfString</span><span class="o">);</span>
<span class="n">SuperSecretAuthorizationActivity</span><span class="o">.</span><span class="na">this</span><span class="o">.</span><span class="na">setMessage</span><span class="o">(</span><span class="n">SuperSecretAuthorizationActivity</span><span class="o">.</span><span class="na">this</span><span class="o">.</span><span class="na">getString</span><span class="o">(</span><span class="mi">2130968590</span><span class="o">));</span>
<span class="n">Boolean</span> <span class="n">localBoolean</span> <span class="o">=</span> <span class="n">Boolean</span><span class="o">.</span><span class="na">valueOf</span><span class="o">(</span><span class="kc">true</span><span class="o">);</span>
<span class="k">return</span> <span class="n">localBoolean</span><span class="o">;</span>
<span class="o">}</span>
<span class="k">catch</span> <span class="o">(</span><span class="n">Exception</span> <span class="n">localException</span><span class="o">)</span>
<span class="o">{</span>
<span class="o">}</span>
<span class="k">return</span> <span class="n">Boolean</span><span class="o">.</span><span class="na">valueOf</span><span class="o">(</span><span class="kc">false</span><span class="o">);</span>
<span class="o">}</span></code></pre></figure>
<p>登录时除了传送email和password外，还会提交应用的signature值。
写了一个小应用来获取apk的签名值，关键代码如下：</p>
<figure class="highlight"><pre><code class="language-java" data-lang="java"><span class="kd">public</span> <span class="n">String</span> <span class="nf">getSingInfo</span><span class="o">(</span><span class="n">String</span> <span class="n">packageName</span><span class="o">)</span> <span class="o">{</span>
<span class="k">try</span> <span class="o">{</span>
<span class="n">PackageInfo</span> <span class="n">packageInfo</span> <span class="o">=</span> <span class="n">getPackageManager</span><span class="o">().</span><span class="na">getPackageInfo</span><span class="o">(</span>
<span class="n">packageName</span><span class="o">,</span> <span class="n">PackageManager</span><span class="o">.</span><span class="na">GET_SIGNATURES</span><span class="o">);</span>
<span class="n">Signature</span><span class="o">[]</span> <span class="n">signs</span> <span class="o">=</span> <span class="n">packageInfo</span><span class="o">.</span><span class="na">signatures</span><span class="o">;</span>
<span class="n">Signature</span> <span class="n">sign</span> <span class="o">=</span> <span class="n">signs</span><span class="o">[</span><span class="mi">0</span><span class="o">];</span>
<span class="n">String</span> <span class="n">signChars</span> <span class="o">=</span> <span class="k">new</span> <span class="n">String</span><span class="o">(</span><span class="n">sign</span><span class="o">.</span><span class="na">toChars</span><span class="o">());</span>
<span class="n">System</span><span class="o">.</span><span class="na">out</span><span class="o">.</span><span class="na">println</span><span class="o">(</span><span class="n">signChars</span><span class="o">);</span>
<span class="n">Log</span><span class="o">.</span><span class="na">d</span><span class="o">(</span><span class="s">"signChars"</span><span class="o">,</span> <span class="n">signChars</span><span class="o">);</span>
<span class="n">signChars</span> <span class="o">=</span> <span class="n">signChars</span> <span class="o">+</span> <span class="s">"\n"</span> <span class="o">+</span> <span class="n">parseSignature</span><span class="o">(</span><span class="n">sign</span><span class="o">.</span><span class="na">toByteArray</span><span class="o">());</span>
<span class="k">return</span> <span class="n">signChars</span><span class="o">;</span>
<span class="o">}</span> <span class="k">catch</span> <span class="o">(</span><span class="n">Exception</span> <span class="n">e</span><span class="o">)</span> <span class="o">{</span>
<span class="n">e</span><span class="o">.</span><span class="na">printStackTrace</span><span class="o">();</span>
<span class="k">return</span> <span class="s">""</span><span class="o">;</span>
<span class="o">}</span>
<span class="o">}</span></code></pre></figure>
<p>得到了原版apk的签名，抓包时提交正确的signature值，可以跟服务器正常交互。
登录数据包为:
identity=base64(用户名)&secret=base64(密码)=&integrityid=APK签名值</p>
<p>服务器返回信息为：</p>
<figure class="highlight"><pre><code class="language-javascript" data-lang="javascript"><span class="p">{</span><span class="s2">"response"</span><span class="p">:{</span><span class="s2">"status"</span><span class="p">:</span><span class="s2">"failure"</span><span class="p">,</span><span class="s2">"msg"</span><span class="p">:</span><span class="s2">"Login failed"</span><span class="p">},</span><span class="s2">"timeStamp"</span><span class="p">:</span><span class="s2">"1379429423"</span><span class="p">,</span><span class="s2">"tZ"</span><span class="p">:</span><span class="s2">"America/New_York"</span><span class="p">,</span><span class="s2">"reqResourceId"</span><span class="p">:</span><span class="s2">"webchal.isis.poly.edu"</span><span class="p">,</span><span class="s2">"clientId"</span><span class="p">:{</span><span class="s2">"identitySig"</span><span class="p">:</span><span class="s2">"d033e22ae348aeb5660fc2140aec35850c4da997"</span><span class="p">,</span><span class="s2">"role"</span><span class="p">:</span><span class="s2">"anonymous"</span><span class="p">,</span><span class="s2">"accessToken"</span><span class="p">:</span><span class="s2">"YWRtaW46YW5vbnltb3VzOndlYmNoYWwuaXNpcy5wb2x5LmVkdQ=="</span><span class="p">}}</span></code></pre></figure>
<p>经过多次尝试，最终发现登录时增加一个role字段，值为base64(‘admin’)时，可以直接通过验证。
服务器返回信息为</p>
<div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>Key: Yo dawg I heard you leik to derp so i put a herp in your derp so you could herpderp while you derpderp
</code></pre></div></div>
<h3 id="references">References</h3>
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<li><a href="http://pallergabor.uw.hu/androidblog/dalvik_opcodes.html">http://pallergabor.uw.hu/androidblog/dalvik_opcodes.html</a></li>
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