pwnable

step by step

 https://pwnable.kr/play.php

连接上,查看文件

input.c内容：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <arpa/inet.h>

int main(int argc, char* argv[], char* envp[]){
        printf("Welcome to pwnable.kr
");
        printf("Let's see if you know how to give input to program
");
        printf("Just give me correct inputs then you will get the flag :)
");

        // argv
        if(argc != 100) return 0;
        if(strcmp(argv['A'],"x00")) return 0;
        if(strcmp(argv['B'],"x20x0ax0d")) return 0;
        printf("Stage 1 clear!
");

        // stdio
        char buf[4];
        read(0, buf, 4);
        if(memcmp(buf, "x00x0ax00xff", 4)) return 0;
        read(2, buf, 4);
        if(memcmp(buf, "x00x0ax02xff", 4)) return 0;
        printf("Stage 2 clear!
");

        // env
        if(strcmp("xcaxfexbaxbe", getenv("xdexadxbexef"))) return 0;
        printf("Stage 3 clear!
");

        // file
        FILE* fp = fopen("x0a", "r");
        if(!fp) return 0;
        if( fread(buf, 4, 1, fp)!=1 ) return 0;
        if( memcmp(buf, "x00x00x00x00", 4) ) return 0;
        fclose(fp);
        printf("Stage 4 clear!
");

        // network
        int sd, cd;
        struct sockaddr_in saddr, caddr;
        sd = socket(AF_INET, SOCK_STREAM, 0);
        if(sd == -1){
                printf("socket error, tell admin
");
                return 0;
        }
        saddr.sin_family = AF_INET;
        saddr.sin_addr.s_addr = INADDR_ANY;
        saddr.sin_port = htons( atoi(argv['C']) );
        if(bind(sd, (struct sockaddr*)&saddr, sizeof(saddr)) < 0){
                printf("bind error, use another port
");
                return 1;
        }
        listen(sd, 1);
        int c = sizeof(struct sockaddr_in);
        cd = accept(sd, (struct sockaddr *)&caddr, (socklen_t*)&c);
        if(cd < 0){
                printf("accept error, tell admin
");
                return 0;
        }
        if( recv(cd, buf, 4, 0) != 4 ) return 0;
        if(memcmp(buf, "xdexadxbexef", 4)) return 0;
        printf("Stage 5 clear!
");

        // here's your flag
        system("/bin/cat flag");
        return 0;
}

看出来，要一关一关通过各种输入，然后可以执行system("/bin/cat flag")。

参考博客：https://r00tk1ts.github.io/2018/03/06/input/

然后在/tmp/input目录建立时，建立失败，原因是存在，所以进去看看，发现：

 有文件，cat一下py，发现是这个题的payload，直接运行了一下，发现没问题，只差建立一个软链接：

ln -s /home/input2/flag flag

建立链接后，运行得到flag。

当然还是自己做做看

我的payload：

import os
import socket
import time
import subprocess

stdinr,stdinw = os.pipe()
stderrr,stderrw = os.pipe()

#argv
args = list("a"*99)
args[ord('A')-1] = ""
args[ord('B')-1] = "x20x0ax0d"
args[ord("C")-1] = "8888"
#stdio
os.write(stdinw,"x00x0ax00xff")
os.write(stderrw,"x00x0ax02xff")

#env
envir = {"xdexadxbexef":"xcaxfexbaxbe"}

#file
f = open("x0a","w")
f.write("x00"*4)
f.close()

pro = subprocess.Popen(["/home/input2/input"]+args,stdin=stdinr,stderr=stderrr,env=envir)

#network
s = socket.socket(socket.AF_INET,socket.SOCK_STREAM)

time.sleep(2)
s.connect(("127.0.0.1",8888))
s.send("xdexadxbexef")
s.close()

在子进程中打开一个程序，并通过管道将父进程构造的参数传到子进程的程序中

使用到的知识：

subprocess：https://www.cnblogs.com/Security-Darren/p/4733368.html