2015-11-30 10:04:26

multipart/form-data PHP和Java通用的WAF绕过方法

依旧是multipart/form-data,去年的时候说道了利用PHP的特性去绕过WAF.轻松绕各种WAF的POST注入、跨站防御(比如安全狗)

原文简单的描述了PHP在处理POST请求的时候会解析multipart/form-data的内容。

那么这个multipart/form-data到底是个啥呢?

1

大概长成上面这样.HTML代码就更加简单了:

<!DOCTYPE html> 
<html> 
<head> 
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> 
<title>yzmm - p2j.cn</title> 
</head> 
<body> 
  <form action="http://192.168.199.151/index.php" method="POST" enctype="multipart/form-data"> 
       File:<input type="file" name="file" /><br/> 
        ID:<input type="text" name="id" value="select 1 from mysql.user--" style="width:250px;" / ><br/> 
        <input type="submit" value="提交" /> 
    </form> 
</body> 
</html>

这个特性其实并不只是PHP的专利,许多其他语言的MVC框架为了简化操作也有可能会做类似PHP FILES解析。虽说原生的JSP/Servlet是不支持解析multipart的.但在Java语言中当今最火的SpringMVC、Struts2都做了一样的事情。你可能经常会看到如下的Spring MVC代码:

import javax.servlet.http.HttpServletRequest; 
import javax.servlet.http.HttpServletResponse; 
import org.springframework.stereotype.Controller; 
import org.springframework.web.bind.annotation.RequestMapping; 
import org.springframework.web.bind.annotation.RequestParam; 
import org.springframework.web.multipart.MultipartFile; 
@Controller 
public class TestController { 
  @RequestMapping("/test1.aspx") 
  public void test1(HttpServletRequest request,HttpServletResponse response){ 
    System.out.println("test1.aspx:"+request.getParameter("username")); 
  } 
  @RequestMapping("/test2.aspx") 
  public void test2(@RequestParam(value = "file", required = false) MultipartFile file,HttpServletRequest request,HttpServletResponse response){ 
    System.out.println("test2.aspx:"+request.getParameter("username")); 
    System.out.println("文件名:"+file.getOriginalFilename()); 
  } 
}

然后是HttpClient客户端测试代码,用于发送HTTP Multipart测试请求:

import java.io.File; 
import java.io.IOException; 
import org.apache.commons.io.IOUtils; 
import org.apache.http.HttpEntity; 
import org.apache.http.client.methods.CloseableHttpResponse; 
import org.apache.http.client.methods.HttpPost; 
import org.apache.http.entity.ContentType; 
import org.apache.http.entity.mime.MultipartEntityBuilder; 
import org.apache.http.impl.client.CloseableHttpClient; 
import org.apache.http.impl.client.HttpClients; 
public class MultipartTest { 
  public static void main(String[] args) { 
    CloseableHttpClient httpClient = HttpClients.createDefault(); 
    HttpPost uploadFile = new HttpPost("http://localhost:8080/test/test1.aspx"); 
    MultipartEntityBuilder builder = MultipartEntityBuilder.create(); 
    builder.addTextBody("username", "admin", ContentType.TEXT_PLAIN); 
    builder.addTextBody("password", "123456", ContentType.TEXT_PLAIN); 
    builder.addBinaryBody("file", new File("/Users/yz/Downloads/bd_logo1_31bdc765.png"), ContentType.APPLICATION_OCTET_STREAM, "pic"); 
    HttpEntity multipart = builder.build(); 
    uploadFile.setEntity(multipart); 
    try { 
      CloseableHttpResponse response = httpClient.execute(uploadFile); 
      HttpEntity responseEntity = response.getEntity(); 
      System.err.println(IOUtils.toString(responseEntity.getContent())); 
    } catch (IOException e) { 
      e.printStackTrace(); 
    } 
  } 
}

pom 依赖的jar:

<dependency> 
      <groupId>org.apache.httpcomponents</groupId> 
      <artifactId>httpcore</artifactId> 
      <version>4.4.4</version> 
    </dependency> 
    <dependency> 
      <groupId>org.apache.httpcomponents</groupId> 
      <artifactId>httpclient</artifactId> 
      <version>4.5.1</version> 
    </dependency> 
    <dependency> 
      <groupId>org.apache.httpcomponents</groupId> 
      <artifactId>httpasyncclient</artifactId> 
      <version>4.1.1</version> 
    </dependency> 
    <dependency> 
      <groupId>org.apache.httpcomponents</groupId> 
      <artifactId>httpmime</artifactId> 
      <version>4.5.1</version> 
    </dependency> 
    <dependency> 
      <groupId>commons-io</groupId> 
      <artifactId>commons-io</artifactId> 
      <version>2.4</version> 
    </dependency>

test1.do是一个最普通的Http请求Mapping,如果当前请求类型是一个multipart请求Spring MVC会将解析好的multipart放到request里面(其实是Spring MVC包装了一个HTTP请求,类名是:org.springframework.web.multipart.support.DefaultMultipartHttpServletRequest)。于是我们在控制层就拿到了multipart里的username参数。

毫无疑问,使用MultipartTest的测试代码去请求test1.aspx会输出multipart内的username的值:admin.

2

Struts2实现方式和SpringMVC大同小异,同样的也自动的利用commons-fileupload做了HTTP解析。

3

import javax.servlet.http.HttpServletRequest; 
import org.apache.struts2.ServletActionContext; 
import com.opensymphony.xwork2.ActionSupport; 
public class Test extends ActionSupport { 
  private static final long serialVersionUID = 1L; 
  @Override 
  public String execute() throws Exception { 
    HttpServletRequest request = ServletActionContext.getRequest(); 
    System.out.println(request.getParameter("username")); 
    return "input"; 
  } 
}

那么为什么一个看似很简单的表单数据请求解析的功能会让很多的WAF蒙了呢?究其原因主要还是因为HTTP请求解析的复杂性和来自客户端的数据不确定性。因为上传一个几十M甚至更大的文件需求再平常不过了,如果WAF完整的去解析这个InputStream会消耗大量的服务器性能有点得不偿失。

另一个原因是由于实现HTTP请求的RFC的差异性导致次类请求解析得不一致或者解析错误的情况。因为multipart解析出问题的还不少。去年PHP和Apache Commons FileUpload 就出过DOS漏洞。

Apache Commons FileUpload 和 Apache Tomcat 拒绝服务

Multipart  boundary  边界检查问题(分割线长度大于4091的)导致拒绝服务(死循环)

PHP曝DOS漏洞可致CPU灌满 涉及多个PHP版本

那么问题来了,各位同学的SQL注入和Struts2的命令执行漏洞真的修好了吗?看看loopx9牛的这个漏洞就知道了 WooYun: 百度某站st2命令执行(独特执行姿势)

赶紧回家修补丁吧。

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