Okay this is getting really old.
This is a problem with almost any service that allows multiple
wild-card characters. UW-IMAPD is another example where this
type of exploit works and has been discussed in great detail
in the past. The only difference here is that the ftpd doesn't
allow a compile time limit to the number of wildcards.
The attack specifically requires that the ftproot has a rather
large directory structure or else the wildcards are parsed
quickly (I.E. the ftp server must be huge). If this is the case
than you shouldn't be allowing wildcards AT ALL, regardless of
what kind of service it is. Aside from that who the hell uses
wu-ftpd for large sites anymore? It's performance without
wildcards is pretty dismal to start with.
-sb
iDEFENSE Labs wrote:
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.
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 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.
