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[分享]pwnable.kr lotto day11
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发表于: 2021-1-13 21:31
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flag 只对创建者 lotto_pwn 和 root 可读，而我们登录的用户是 lotto，无读权限。lotto 对 lotto_pwn 和 lotto 开放读和执行权限，而且权限里面有 s，因此 lotto 用户在执行这个文件时会被赋予与用户 lotto_pwn 相同权限。
我们的目标是执行 system("/bin/cat flag")，这要求 match 的值等于 6 。
由
知，lotto 数组中的每一个数都要与 submit 数组中的每一个数比较，如果相等，则 match++ ，submit 的值是我们手动输入的，他是字符型数组，lotto 的值是 /dev/urandom 生成的伪随机数，其 ASCII 值属于 1 ~ 45。其中可打印字符包括 !"#$%&'()+,- 十三个。
此处本应是只比较 6 次，这里写成了比较 36 次。*
所以我们可以输入 6 个相同的数，这样次要生成的随机数中存在一个与输入的数相等的，match 的值就为 6
红框内为 flag
本地执行
本地执行时需建立 flag 的软链接
remote
#include <stdio.h>#include <stdlib.h>#include <string.h>#include <fcntl.h>unsigned char submit[6];
void play(){ int i;
printf("Submit your 6 lotto bytes : ");
fflush(stdout);
int r;
r = read(0, submit, 6);
printf("Lotto Start!\n");
//sleep(1);
// generate lotto numbers
int fd = open("/dev/urandom", O_RDONLY);
if(fd==-1){
printf("error. tell admin\n");
exit(-1);
}
unsigned char lotto[6];
if(read(fd, lotto, 6) != 6){
printf("error2. tell admin\n");
exit(-1);
}
for(i=0; i<6; i++){
lotto[i] = (lotto[i] % 45) + 1; // 1 ~ 45
}
close(fd);
// calculate lotto score
int match = 0, j = 0;
for(i=0; i<6; i++){
for(j=0; j<6; j++){
if(lotto[i] == submit[j]){
match++;
}
}
}
// win!
if(match == 6){
system("/bin/cat flag");
}
else{
printf("bad luck...\n");
}
}void help(){
printf("- nLotto Rule -\n");
printf("nlotto is consisted with 6 random natural numbers less than 46\n");
printf("your goal is to match lotto numbers as many as you can\n");
printf("if you win lottery for *1st place*, you will get reward\n");
printf("for more details, follow the link below\n");
printf("http://www.nlotto.co.kr/counsel.do?method=playerGuide#buying_guide01\n\n");
printf("mathematical chance to win this game is known to be 1/8145060.\n");
}int main(int argc, char* argv[]){
// menu
unsigned int menu;
while(1){
printf("- Select Menu -\n");
printf("1. Play Lotto\n");
printf("2. Help\n");
printf("3. Exit\n");
scanf("%d", &menu);
switch(menu){
case 1:
play();
break;
case 2:
help();
break;
case 3:
printf("bye\n");
return 0;
default:
printf("invalid menu\n");
break;
}
}
return 0;
}#include <stdio.h>#include <stdlib.h>#include <string.h>#include <fcntl.h>unsigned char submit[6];
void play(){ int i;
printf("Submit your 6 lotto bytes : ");
fflush(stdout);
int r;
r = read(0, submit, 6);
printf("Lotto Start!\n");
//sleep(1);
// generate lotto numbers
int fd = open("/dev/urandom", O_RDONLY);
if(fd==-1){
printf("error. tell admin\n");
exit(-1);
}
unsigned char lotto[6];
if(read(fd, lotto, 6) != 6){
printf("error2. tell admin\n");
exit(-1);
}
for(i=0; i<6; i++){
lotto[i] = (lotto[i] % 45) + 1; // 1 ~ 45
}
close(fd);
// calculate lotto score
int match = 0, j = 0;
for(i=0; i<6; i++){
for(j=0; j<6; j++){
if(lotto[i] == submit[j]){
match++;
}
}
}
// win!
if(match == 6){
system("/bin/cat flag");
}
else{
printf("bad luck...\n");
}
}void help(){
printf("- nLotto Rule -\n");
printf("nlotto is consisted with 6 random natural numbers less than 46\n");
printf("your goal is to match lotto numbers as many as you can\n");
printf("if you win lottery for *1st place*, you will get reward\n");
printf("for more details, follow the link below\n");
[培训]内核驱动高级班，冲击BAT一流互联网大厂工作，每周日13:00-18:00直播授课
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我刚刚学，打算通过分享 wp敦促自己学习
 努力做到一天一题刷完 pwnable.kr |
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