[UNIX] Snif File Disclosure Vulnerability

From: SecuriTeam (support_at_securiteam.com)
Date: 12/01/03

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Date: 1 Dec 2003 13:46:48 +0200

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      Snif File Disclosure Vulnerability
    ------------------------------------------------------------------------

    SUMMARY

     <http://www.bitfolge.de/index.php?l=en&s=snif&style=earth> Snif is "a
    simple and nice index file". A vulnerability in the product allows remote
    attackers to download files that reside outside the bound HTML root
    directory.

    DETAILS

    Vulnerable systems:
     * Snif versions prior to 1.2.5

    Immune systems:
     * Snif version 1.2.5

    The script takes two query-strings "path" and "download" from the URL and
    concatenates them. It stores the result in the variable $filename which is
    the file to be downloaded. By default the value for the path variable is
    set to NULL and there is no error checking to see if the "download"
    querystring is outside the default directory. Thus an attacker could
    change the "download" querystring to any file on the file system while
    leaving the "path" NULL. This would allow him/her to download the file
    requested.

    Vulnerable code:
    // this handles the download requests
    if ($_GET["download"]!="") {
      // This is were the path checking fails
      $filename = $path.$_GET["download"];
      if (
        !file_exists($filename)
        OR fileIsHidden($_GET["download"])
        OR (substr(strtolower($_GET["download"]), -4)==".php" AND
    !$allowPHPDownloads)) {
        
        Header("HTTP/1.0 404 Not Found");
        echo "<b>Error: File not found.</b><br><br>we suggest you
        <a href=\"".$_SERVER["HTTP_REFERER"]."\">go back</a>";
      } else {
        Header("Content-Length: ".filesize($filename));
        Header("Content-Type: application/x-download");
        Header("Content-Disposition: attachment;
    filename=".$_GET["download"]);
        readfile($filename);
      }
      die();
    }

    Exploit:
    By requesting the following URL
    http://www.yourserver.com/snif/index.php?download=/etc/passwd, it is
    possible to download the /etc/passwd file.

    Solution:
    Download version 1.2.5 from the vendors homepage
    <http://www.bitfolge.de/snif> http://www.bitfolge.de/snif.

    Vendor timeline:
    24 November 2003 - Bug Found
    25 November 2003 - Vendor Contacted
    26 November 2003 - Vendor Fixed Bug

    ADDITIONAL INFORMATION

    The information has been provided by <mailto:jay@j-security.co.uk> J.

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