WU-FTPD File Globbing Denial of Service Vulnerability

iDEFENSE Security Advisory 02.25.05
www.idefense.com/application/poi/display?id=207&type=vulnerabilities
February 25, 2005

I. BACKGROUND

WU-FTPD is an ftp daemon for Unix systems developed at Washington 
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 
resource exhaustion.

The vulnerability specifically exists in the wu_fnmatch() function in
wu_fnmatch.c. When a pattern containing a '*' character is supplied as 
input, the function calls itself recursively on a smaller substring. By 
supplying a string which contains a large number of '*' characters, the 
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 
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 
services provided by the system for the period of the attack.

IV. DETECTION

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

V. WORKAROUND
Consider disabling the ftpd. If this is not viable as an option, 
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.

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X. LEGAL NOTICES

Copyright (c) 2005 iDEFENSE, Inc.

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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
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or consequential loss or damage arising from use of, or reliance on,
this information.