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 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. _______________________________________________ Full-Disclosure - We believe in it. Charter: http://lists.netsys.com/full-disclosure-charter.html