[UNIX] Samba 3.x.x Wildcard Characters DoS

From: SecuriTeam (support_at_securiteam.com)
Date: 11/09/04

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Date: 9 Nov 2004 18:29:06 +0200

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      Samba 3.x.x Wildcard Characters DoS
    ------------------------------------------------------------------------

    SUMMARY

    A remote attacker could cause and smbd process to consume abnormal amounts
    of system resources due to an input validation error when matching
    filenames containing wildcard characters.

    DETAILS

    Vulnerable Systems:
     * Samba versions 3.0.x up to 3.0.7

    A bug in the input validation routines used to match filename strings
    containing wildcard characters may allow a user to consume more than
    normal amounts of CPU cycles thus impacting the performance and response
    of the server. In some circumstances the server can become entirely
    unresponsive.

    Protecting Unpatched Servers:
    The Samba Team always encourages users to run the latest stable release as
    a defense of against attacks. However, under certain circumstances it may
    not be possible to immediately upgrade important installations. In such
    cases, administrators should
    read the "Server Security" documentation found at
    <http://www.samba.org/samba/docs/server_security.html>
    http://www.samba.org/samba/docs/server_security.html.

    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.

    Patch Availability:
    A patch for Samba 3.0.7 (samba-3.0.7-CAN-2004-0930.patch) is available
    from <http://www.samba.org/samba/ftp/patches/security/>
    http://www.samba.org/samba/ftp/patches/security/. The patch has been
    signed with the "Samba Distribution Verification Key" (ID F17F9772).

    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

    Technical Details:
    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.

    ADDITIONAL INFORMATION

    The information has been provided by Karol Wiesek.
    The original article can be found at:
    <http://www.idefense.com/application/poi/display?id=156&type=vulnerabilities> http://www.idefense.com/application/poi/display?id=156&type=vulnerabilities

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