FWD: iDEFENSE Security Advisory 02.25.05: WU-FTPD File Globbing Denial of Service Vulnerability

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Hello again,

I've just had this forwarded to me from a member of the Debian security
team. I was wondering if there was someone who has spotted it already
and is working on it, otherwise I'll try and find time to work on it
myself over the weekend.=20

I haven't actually had chance to check the code yet, but as a quick
thought, the simplest fix might just be to limit the number of
recursions of wu_fnmatch to a reasonable number, failing with an error
if the limit is reached.

----- Forwarded message from iDEFENSE Labs <[email protected]> ---=
--

=46rom: iDEFENSE Labs <[email protected]>
Date: Fri, 25 Feb 2005 12:43:54 -0500
To: [email protected], [email protected]
Subject: iDEFENSE Security Advisory 02.25.05: WU-FTPD File Globbing Denial =
of Service Vulnerability

WU-FTPD File Globbing Denial of Service Vulnerability

iDEFENSE Security Advisory 02.25.05
www.idefense.com/application/poi/display?id=3D207&type=3Dvulnerabilities
February 25, 2005

I. BACKGROUND

WU-FTPD is an ftp daemon for Unix systems developed at Washington=20
University. More information is available at:

    http://www.wu-ftpd.org/

II. DESCRIPTION

Remote exploitation of an input validation vulnerability in version
2.6.2 of WU-FPTD could allow for a denial of service of the system by=20
resource exhaustion.

The vulnerability specifically exists in the wu_fnmatch() function in
wu_fnmatch.c. When a pattern containing a '*' character is supplied as=20
input, the function calls itself recursively on a smaller substring. By=20
supplying a string which contains a large number of '*' characters, the=20
system will take a long time to return the results, during which time it

will be using a large amount of CPU time.

III. ANALYSIS

After a user logs into the ftpd, an attacker can send a simple command=20
which will cause high CPU utilization.

To exploit this vulnerability, a simple ftp client is sufficient. Once
logged  in, either anonymously or as an authenticated user, issuing the
following command will cause the machine to become less responsive.

ftp> dir ***************************************************************
         ***************************************************************
         ***************************************************************
         **.*

By re-connecting and issuing the command multiple times, the system can
be made completely unresponsive. This may prevent legitimate access to=20
services provided by the system for the period of the attack.

IV. DETECTION

iDEFENSE has confirmed the existence of this vulnerability in version=20
2.6.2 and 2.6.1 of WU-FTPD. It is suspected that previous versions are=20
also affected by this vulnerability.

V. WORKAROUND
Consider disabling the ftpd. If this is not viable as an option,=20
consider disabling anonymous access. Disabling anonymous access will not

prevent local users from exploiting this vulnerability.

VI. VENDOR RESPONSE

No vendor response received.

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
names CAN-2005-0256 to these issues. This is a candidate for inclusion
in the CVE list (http://cve.mitre.org), which standardizes names for
security problems.

VIII. DISCLOSURE TIMELINE

02/09/2005  Initial vendor notification - No response
02/18/2005  Initial vendor notification - No response
02/25/2005  Public disclosure

IX. CREDIT

Adam Zabrocki (pi3 / pi3ki31ny) is credited with this discovery.

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

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

X. LEGAL NOTICES

Copyright (c) 2005 iDEFENSE, 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 [email protected] 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.


----- End forwarded message -----

--=20
Chris Butler    <[email protected]>
 Debian WU-FTPD package maintainer
   GnuPG Key ID: 1024D/D097A261

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