Public Vulnerability Reports

Ethereal OSPF Protocol Dissector Buffer Overflow Vulnerability

12.09.05

BACKGROUND

Ethereal is a full featured open source network protocol analyzer.

For more information, see http://www.ethereal.com/

DESCRIPTION

Remote exploitation of an input validation vulnerability in the OSPF
protocol dissectors within Ethereal, as included in various vendors
operating system distributions, could allow attackers to crash the
vulnerable process or potentially execute arbitrary code.

The affected Ethereal component is used to analyse Open Shortest Path
First (OSPF) Interior Gateway Protocol (IGP), as specified in RFC-2178.

The vulnerability specifically exists due to no bounds checking being
performed in the dissect_ospf_v3_address_prefix() function. This
function takes user-supplied binary data and attempts to convert it into
a human readable string. This function uses a fixed length buffer on
the stack to store the constructed string but performs no checks on the
length of the input. If the generated output length from the input
exceeds the size of the buffer, a stack-based overflow occurs.

ANALYSIS

Successful exploitation allows remote attackers to perform a DoS against
a running instance of Ethereal and may, under certain conditions,
potentially allow the execution of arbitrary code. As the overflow
string is generated from a format string converting binary values into
their hexadecimal (base 16) equivalent characters, it can contain only a
limited subset of all possible characters, and the length of an
overflow is only able to be controlled to within the three characters.
This may prevent exploit ability on some platforms; however, it may be
possible that these constraints will not prevent exploitation on
others.

DETECTION

iDefense has confirmed the existence of this vulnerability in the
ethereal-0.10.12 RPM from Red Hat Fedora Core 3. It is suspected that
previous versions containing the OSPF dissector code are also
vulnerable.

WORKAROUND

Disable the OSPF packet dissector in Ethereal by performing the
following actions as the user invoking Ethereal, typically root.

Create the .ethereal directory:

 # mkdir ~/.ethereal

You can safely ignore the following error:

 mkdir: cannot create directory '/root/.ethereal': File exists

Add the OSPF dissector to the list of protocols to ignore.

 # echo ospf >> ~/.ethereal/disabled_protos

This workaround will prevent Ethereal from parsing the contents of OSPF
packets, which prevents exposure to the vulnerability.

VENDOR RESPONSE

A source patch is available from the main ethereal SVN Repository:

http://anonsvn.ethereal.com/viewcvs/viewcvs.py/trunk/epan/dissectors/
 packet-ospf.c?rev=16507&view=markup

CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CVE-2005-3651 to this issue. This is a candidate for inclusion in
the CVE list (http://cve.mitre.org), which standardizes names for
security problems.

DISCLOSURE TIMELINE

11/14/2005 Initial vendor notification
11/14/2005 Initial vendor response
12/09/2005 Public disclosure

CREDIT

The discoverer of this vulnerability wishes to remain anonymous.

Get paid for vulnerability research
http://www.iDefense.com/poi/teams/vcp.jsp

Free tools, research and upcoming events
http://labs.iDefense.com

LEGAL NOTICES

Copyright © 2005 Verisign, Inc.

Permission is granted for the redistribution of this alert
electronically. It may not be edited in any way without the express
written consent of iDefense. If you wish to reprint the whole or any
part of this alert in any other medium other than electronically, please
email customerservice@iDefense.com for permission.

Disclaimer: The information in the advisory is believed to be accurate
at the time of publishing based on currently available information. Use
of the information constitutes acceptance for use in an AS IS condition.
There are no warranties with regard to this information. Neither the
author nor the publisher accepts any liability for any direct, indirect,
or consequential loss or damage arising from use of, or reliance on,
this information.