Public Vulnerability Reports

Samba SMBD Remote Denial of Service Vulnerability

11.08.04

BACKGROUND

Samba is an Open Source/Free Software suite that provides seamless file
and print services to SMB/CIFS clients.

DESCRIPTION

Remote exploitation of an input validation error in Samba could allow an
attacker to consume system resources and potentially cause the target
system to crash.

The problem specifically exists within the ms_fnmatch() routine which
upon parsing '*' characters within a pattern will fall into an
exponentially growing loop. The responsible section of vulnerable code
appears here:

case '*': 
    for (; *n; n++) {
        if (ms_fnmatch(p, n) == 0) return 0;
        }    
        break;

An authenticated remote attacker can cause a resource exhaustion attack
by sending multiple malformed commands to an affected server. A request
as simple as 'dir ***********************************************z' can
trigger this condition leading to 100% CPU usage.

ANALYSIS

Successful exploitation allows authenticated remote attackers to exhaust
CPU resources. This attack takes very little bandwidth and can, in some
cases, cause the machine to stop responding. Multiple attacks can be
launched in parallel which can make this attack more effective.

DETECTION

iDEFENSE has confirmed the existence of this vulnerability in Samba
versions 3.0.4 and 3.0.7. It is suspected that all versions of Samba up
to and including 3.0.7 are vulnerable.

WORKAROUND

Restricting access to the server by using the "hosts allow" setting in
smb.conf and/or applying firewall rules may help mitigate this
vulnerability.

VENDOR RESPONSE

3.0.7 patch:
http://www.samba.org/samba/ftp/patches/security/samba-3.0.7-CAN-2004-0930.patch

3.0.7 patch signature:
http://www.samba.org/samba/ftp/patches/security/samba-3.0.7-CAN-2004-0930.patch.asc

CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
names CAN-2004-0930 to these issues. This is a candidate for inclusion
in the CVE list (http://cve.mitre.org), which standardizes names for
security problems.

DISCLOSURE TIMELINE

09/29/2004   iDEFENSE clients notified
09/29/2004   Initial vendor notification
09/30/2004   Initial vendor response
11/08/2004   Coordinated public disclosure

CREDIT

Karol Wiesek is credited with this discovery.

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LEGAL NOTICES

Copyright © 2004 Verisign, Inc.

Permission is granted for the redistribution of this alert
electronically. It may not be edited in any way without the express
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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.