Samba SMBD Remote Denial of Service Vulnerability

firewall · 26-11-2004, 05:04 PM

Code:

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.

-----