[UNIX] Ethereal srvloc Buffer Overflow

From: SecuriTeam (support_at_securiteam.com)
Date: 11/02/05

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Date: 2 Nov 2005 09:29:15 +0200

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      Ethereal srvloc Buffer Overflow
    ------------------------------------------------------------------------

    SUMMARY

     <http://www.ethereal.com/> Ethereal is "a full featured open source
    network protocol analyzer".

    Remote exploitation of a buffer overflow vulnerability in the Service
    Location Protocol (srvloc) dissectors within Ethereal allows attackers to
    crash the vulnerable process or execute arbitrary code.

    DETAILS

    Vulnerable Systems:
     * Ethereal version 0.10.12 and earlier

    Immune Systems:
     * Ethereal version 0.10.13 (download
    <http://www.ethereal.com/download.html> here)

    Vulnerable code:
    --------------------------------- Begin Code
    ---------------------------------
    /epan/dissectors/packet-srvloc.c:429

    static guint8*
    unicode_to_bytes(tvbuff_t *tvb, int offset, int length, gboolean
    endianness)
    {
      const char *ascii_text = tvb_get_ptr(tvb, offset, length);
      int i, j=0;
      guint8 c_char, c_char1;
      static guint8 byte_array[255];

      if (endianness) {
        ...
          }
      }
      else
      {
          for (i = 0; i < length; i++) {
            c_char = ascii_text[i];
            if (c_char != 0) {
                byte_array[j] = c_char;
                j++;
            }
          }
      }

      byte_array[j]=0;
      return byte_array;
    }
    ---------------------------------- End Code
    ----------------------------------

    This function is called with a user-controlled length value on line 581 in
    the same file. This allows an attacker to cause an overflow of the
    byte_array array, as values greater than 255 may be specified. In lab
    analysis, it has been demonstrated that there are several interesting
    values beyond this array that make arbitrary code execution possible.

    To cause Ethereal to dissect an arbitrary packet with the srvloc
    dissector, the source or destination port must be set to TCP port 427, and
    the destination port must not be a port with any registered dissector. As
    Ethereal does not keep state, a single spoofed TCP data packet can be used
    to exploit this vulnerability, regardless of whether there are any ports
    listening on either end.

    Exploitation could result in remote root access, as Ethereal must have
    root privileges to open a raw socket.Ethereal is often used by network
    administrators to debug network problems and compromise of a network
    administrators machine can lead to further compromise of the network.

    Workaround:
    When using Ethereal, use the following filter to disable port 427, and
    therefore, automatic srvloc dissection:
            not port 427

    Vendor Status:
    The vendor has addressed this issue in ethereal 0.10.13, available
    fordownload at:
     <http://www.ethereal.com/download.html>
    http://www.ethereal.com/download.html

    CVE Information:
     <http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2005-3184>
    CAN-2005-3184

    Disclosure Timeline:
    12.10.05 - Initial vendor notification
    12.10.05 - Initial vendor response
    20.10.05 - Coordinated public disclosure

    ADDITIONAL INFORMATION

    The information has been provided by iDEFENSE.
    The original article can be found at:
     <http://www.idefense.com/application/poi/display?id=323>
    http://www.idefense.com/application/poi/display?id=323

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