SSRT3509 Potential Security Vulnerability in CIFS/9000 Server (rev.1)

From: Security Alert (secure_at_cup.hp.com)
Date: 05/13/03 

Date: 13 May 2003 08:12:47 -0700

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 **REVISED 01**
 Source: HEWLETT-PACKARD COMPANY
 SECURITY BULLETIN: HPSBUX0303-251
 Originally issued: 18 March 2003
 Last revised: 12 May 2003
 SSRT3509 Potential Security Vulnerability in CIFS/9000 Server
          (rev.1)
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NOTICE: There are no restrictions for distribution of this
Bulletin provided that it remains complete and intact.

The information in the following Security Bulletin should be
acted upon as soon as possible. Hewlett-Packard Company will
not be liable for any consequences to any customer resulting
from customer's failure to fully implement instructions in this
Security Bulletin as soon as possible.

 -----------------------------------------------------------------
PROBLEM: CIFS/9000 Server is potentially vulnerable to altered
         SMB/CIFS network messages.

IMPACT: Potential remote root access.

PLATFORM: All HP9000 servers running CIFS/9000 Server versions up
          through A.01.09.02 on HP-UX 11.0, 11.11(11i), and 11.22

**REVISED 01**
SOLUTION: HP-UX 11.0, 11.11, 11.22
 --> Download and install the CIFS Server 2.2e version
 --> A.01.09.04 or subsequent from software.hp.com.

**REVISED 01**
MANUAL ACTIONS: Yes - Update

 --> HP-UX 11.0, 11.11, 11.22
 --> Download and install the CIFS Server 2.2e version
 --> A.01.09.04 or subsequent from software.hp.com.

AVAILABILITY: CIFS Server 2.2e version A.01.09.04 is available
               now from software.hp.com.

CHANGE SUMMARY: Rev.01 - CIFS Server 2.2e version A.01.09.04
                         available for 11.00, 11.11, 11.22.
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 A. Background

    Note: The following are not vulnerable:

            HP OpenVMS
            HP NonStop Servers
            HP Tru64 UNIX
            HP Secure Web Servers for HP Tru64 UNIX
            HP Secure Web Servers for HP Tru64 OpenVMS

          As further information becomes available HP
          will provide notice of the availability of any
          additional Samba updates through standard security
          bulletin announcements and information will be
          available from your normal HP Services support channel.

    CIFS Server version A.01.09.01 and prior may allow modified
    SMB/CIFS messages to cause smbd to overwrite portions of its
    own process address space. This could potentially be
    exploited to gain root access remotely.

    The latest version of CIFS Server adds checks for proper
    SMB/CIFS messages to prevent invalid smbd memory accesses.

    The Samba team has provided a note describing ways to
    limit exposure to this vulnerability and future potential
    vulnerabilities. Please refer to Section E below.

**REVISED 01**
 -->Note: The HP CIFS Server versions do not map directly to
 --> original Samba versions. Significant Samba fixes,
 --> including security fixes, are backported into the
 --> HP CIFS Server. Specific security-related code was
 --> backported from 2.2.8a into the current HP CIFS Server
 --> source, which is based on Samba 2.2.5. The what(1)
 --> output will show the HP version string, for example:
 --> A.01.09.04. Samba commands such as "smd -V" or
 --> smbstatus will only report the underlying base Samba
 --> version, for example: 2.2.5.

 B. Recommended solution

**REVISED 01**
 -> HP-UX 11.0, 11.11, 11.22

 -> Update to version A.01.09.04 (available on software.hp.com).
 -> This version includes the fixes provided by the binary
 -> replacement files smbd.11.00 (version A.01.09.02) and
 -> smbd.11.00.r1 (A.01.09.03) previously available via FTP
 -> access.

 C. To subscribe to automatically receive future NEW HP Security
    Bulletins from the HP IT Resource Center via electronic
    mail, do the following:

    Use your browser to get to the HP IT Resource Center page
    at:

       http://itrc.hp.com

    Use the 'Login' tab at the left side of the screen to login
    using your ID and password. Use your existing login or the
    "Register" button at the left to create a login, in order to
    gain access to many areas of the ITRC. Remember to save the
    User ID assigned to you, and your password.

    In the left most frame select "Maintenance and Support".

    Under the "Notifications" section (near the bottom of
    the page), select "Support Information Digests".

    To -subscribe- to future HP Security Bulletins or other
    Technical Digests, click the check box (in the left column)
    for the appropriate digest and then click the "Update
    Subscriptions" button at the bottom of the page.

    or

    To -review- bulletins already released, select the link
    (in the middle column) for the appropriate digest.

    NOTE: Using your itrc account security bulletins can be
          found here:
    http://itrc.hp.com/cki/bin/doc.pl/screen=ckiSecurityBulletin

    To -gain access- to the Security Patch Matrix, select
    the link for "The Security Bulletins Archive". (near the
    bottom of the page) Once in the archive the third link is
    to the current Security Patch Matrix. Updated daily, this
    matrix categorizes security patches by platform/OS release,
    and by bulletin topic. Security Patch Check completely
    automates the process of reviewing the patch matrix for
    11.XX systems. Please note that installing the patches
    listed in the Security Patch Matrix will completely
    implement a security bulletin _only_ if the MANUAL ACTIONS
    field specifies "No."

    The Security Patch Check tool can verify that a security
    bulletin has been implemented on HP-UX 11.XX systems providing
    that the fix is completely implemented in a patch with no
    manual actions required. The Security Patch Check tool cannot
    verify fixes implemented via a product upgrade.

    For information on the Security Patch Check tool, see:
    http://www.software.hp.com/cgi-bin/swdepot_parser.cgi/cgi/
    displayProductInfo.pl?productNumber=B6834AA

    The security patch matrix is also available via anonymous
    ftp:

    ftp://ftp.itrc.hp.com/export/patches/hp-ux_patch_matrix/

    On the "Support Information Digest Main" page:
    click on the "HP Security Bulletin Archive".

    The PGP key used to sign this bulletin is available from
    several PGP Public Key servers. The key identification
    information is:

       2D2A7D59
       HP Security Response Team (Security Bulletin signing only)
       <security-alert@hp.com>
       Fingerprint =
         6002 6019 BFC1 BC62 F079 862E E01F 3AFC 2D2A 7D59

    If you have problems locating the key please write to
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 D. To report new security vulnerabilities, send email to

    security-alert@hp.com

    Please encrypt any exploit information using the
    security-alert PGP key, available from your local key
    server, or by sending a message with a -subject- (not body)
    of 'get key' (no quotes) to security-alert@hp.com.

 E. Samba Team notes on protecting an unpatched Samba server

    ************************************
    Protecting an unpatched Samba server
    ************************************

    This is a note on how to provide your Samba server some
    protection against the potential vulnerability even
    if you are unable to upgrade to the fixed version
    immediately. Even if you do upgrade these suggestions
    provide additional levels of protection against possible
    future vulnerabilities.

    Using host based protection
    ---------------------------

    In many installations of Samba the greatest threat comes from
    outside the immediate network. By default Samba will accept
    connections from any host.

    One of the simplest fixes in this case is to use the 'hosts
    allow' and 'hosts deny' options in the Samba smb.conf
    configuration file to only allow access to your server from a
    specific range of hosts. An example might be:

      hosts allow = 127.0.0.1 192.168.2.0/24 192.168.3.0/24
      hosts deny = 0.0.0.0/0

    The above will only allow SMB connections from 'localhost'
    (your own computer) and from the two private networks
    192.168.2 and 192.168.3. All other connections will be
    refused connections as soon as the client sends its first
    packet. The refusal will be marked as a 'not listening on
    called name' error.

    Using interface protection
    --------------------------

    By default Samba will accept connections on any network
    interface that it finds on your system. That means if you
    have a ISDN line or a PPP connection to the Internet then
    Samba will accept connections on those links. This may not be
    what you want.

    You can change this behavior using options like the
    following:

      interfaces = lan* lo0
      bind interfaces only = yes

    that tells Samba to only listen for connections on interfaces
    with a name starting with 'lan' such as lan0, lan1, plus on
    the loopback interface called 'lo0'. The name you will need to
    use depends on what OS you are using. The example above uses
    the common name for ethernet adapters on HP-UX.

    If you use the above and someone tries to make a SMB
    connection to your host over a PPP interface called 'ppp0',
    they will get a TCP connection refused reply. In that
    case no Samba code is run at all as the operating system has
    been told not to pass connections from that interface to any
    process.

    Using a firewall
    ----------------

    Many people use a firewall to deny access to services that
    they do not want exposed outside their network. This can be a
    very good idea, although the methods above should also be used
    in case the firewall is not active for some reason.

    If you are setting up a firewall then you need to know what
    TCP and UDP ports to allow and block. Samba uses the
    following:

      UDP/137 - used by nmbd
      UDP/138 - used by nmbd
      TCP/139 - used by smbd
      TCP/445 - used by smbd

    The last one is important as many older firewall setups may
    not be aware of it, given that this port was only added to
    the protocol in recent years.

    Using a IPC$ share deny
    -----------------------

    If the above methods are not suitable, then you could also
    place a more specific deny on the IPC$ share that is used in
    the vulnerability reported in this bulletin. This allows you
    to offer access to other shares while denying access to IPC$
    from potentially untrustworthy hosts.

    To do that you could use:

      [ipc$]
          hosts allow = 192.168.115.0/24 127.0.0.1
          hosts deny = 0.0.0.0/0

    this would tell Samba that IPC$ connections are not allowed
    from anywhere but the two listed places (localhost and a
    local subnet). Connections to other shares would still be
    allowed. As the IPC$ share is the only share that is always
    accessible anonymously this provides some level of protection
    against attackers that do not know a username/password for
    your host.

    If you use this method then clients will be given an 'access
    denied' reply when they try to access the IPC$ share. That
    means that those clients will not be able to browse shares,
    and may also be unable to access some other resources.

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(c)Copyright 2003 Hewlett-Packard Company
Hewlett-Packard Company shall not be liable for technical or
editorial errors or omissions contained herein. The information
in this document is subject to change without notice.
Hewlett-Packard Company and the names of HP products referenced
herein are trademarks and/or service marks of Hewlett-Packard
Company. Other product and company names mentioned herein may be
trademarks and/or service marks of their respective owners.

 ________________________________________________________________

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--
Yours truly,
HP S/W Security Team
WTEC Cupertino, California
Return-Path: secure@cup.hp.com
Reply-to: security-alert@hp.com

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