So I have taken a challenge to this month to do at least one pwn challenge a day for the entire month of May

Day1

I started with an easy challenge from this site as I am completely new with this category

Name- fd

the description says to connect to the server using ssh and something about file descriptor lets look it up online I got this

More about it can be read on this site

lets login and see what we got

So we have a flag , fd binary and its source c file lets see the source file

char buf[32];
int main(int argc, char* argv[], char* envp[]){
        if(argc<2){
                printf("pass argv[1] a number\n");
                return 0;
        }
        int fd = atoi( argv[1] ) - 0x1234;
        int len = 0;
        len = read(fd, buf, 32);
        if(!strcmp("LETMEWIN\n", buf)){
                printf("good job :)\n");
                system("/bin/cat flag");
                exit(0);
        }
        printf("learn about Linux file IO\n");
        return 0;

}

Intially lines shows that we need to pass 2 arguments for the program to run Further it determines the value of fd using the following logic:- fd= atoi(argv[1])-0x1234

atoi function converts a string to integer

We know fd stands for File Descriptor

Upon furthur reading the source code we find that we need to pass the string LETMEWIN to stdin so as to get the shell so lets see what we got here

For stdin fd is 0 so we need to supply argv[1] equal to 0x1234 so as to get the value 0 and then enter the string to get the flag!! The full solution is shown below