Samba SMBD Remote Denial of Service Vulnerability

iDEFENSE Security Advisory 11.08.04 
www.idefense.com/application/poi/display?id=156&type=vulnerabilities
November 08, 2004

I. BACKGROUND

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

II. 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.

III. 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.

IV. 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.

V. 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.

VI. VENDOR RESPONSE

3.0.7 patch:
http://www.samba.org/samba/ftp/patches/security/samba-3.0.7-CAN-2004-093
0.patch

3.0.7 patch signature:
http://www.samba.org/samba/ftp/patches/security/samba-3.0.7-CAN-2004-093
0.patch.asc

VII. 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.

VIII. 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

IX. CREDIT

Karol Wiesek is credited with this discovery.

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

X. LEGAL NOTICES

Copyright (c) 2004 iDEFENSE, Inc.

Permission is granted for the redistribution of this alert 
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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 
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.