rfc2179.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.


RFC 2179            Network Security For Trade Shows           July 1997


   Tips:

   * "find / -user root -perm -4000 -print" will find any occurrence of
     a setuid file anywhere in the system, including those on NFS
     mounted partitions.
   * "find / -group kmem -perm -2000 -print" will do the same for kmem
     group permissions.

System Directory Ownership and Write Permissions

   Check ownership of all system directories and permissions needed to
   write or modify files. There is no simple way to do this on PC
   operating systems like Windows NT without simply checking all files
   and directories or using a version of "ls" that will list ACLs.

   On Unix systems, a directory with permissions such as "drwxrwxrwx"
   (such as /tmp) is world-writable and anyone can create or modify
   files in such area. Pay special attention to "/" and "/etc". These
   should be owned by some system account-not by an individual user.
   When in doubt, contact the vendor of the system software for
   confirmation of the appropriate directory or file permissions.

Network Services

   Any servers not needed should be disabled. The notorious "R services"
   (rexec, rsh, and rlogin) are particularly prone to security problems
   and should be disabled unless specifically needed.  Pay particular
   attention to trusted hosts files, and be aware of the risk of IP
   spoofing attacks from machines "pretending" to be trusted hosts.

   Tips:

   * On Unix systems, comment out "R services" (rexec, rsh, rlogin) in
     /etc/inetd.conf.
   * Check for other unknown or unneeded services.

Trivial File Transfer Protocol (TFTP)

   TFTP can be an easy way for an intruder to access system files. It is
   good general practice to disable TFTP.  If TFTP is needed, verify
   that only files targeted for export are accessible.  A simple way to
   check security is to attempt to tftp files such as /etc/passwd or
   /etc/motd to check accessiblity of system files.








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RFC 2179            Network Security For Trade Shows           July 1997


TCP Connection Monitoring

   Public domain software (TCP Wrappers or "tcpd" for Unix systems)
   allow restriction and monitoring of TCP connections on a host by host
   basis. Systems can be configured to notify an administrator and
   syslog when any unauthorized party attempts to access the host. This
   software is available from:

   * ftp://info.cert.org/pub/tools/tcp_wrappers/

BIND (Berkeley Internet Name Daemon)

   Earlier versions of BIND have been prone to various attacks. If a
   host is going to be acting as DNS, use the latest version of BIND.
   It is available at:

   * ftp://ftp.isc.org/isc/bind

Sendmail and Mailer Security

   A great number of previous versions of Sendmail have known security
   holes.  Check installed sendmail for the most recent version.
   Alternatively, consult the operating system vendor to get the most
   recent release for the platform.

Web Server Scripting Security

   All Web server scripts and binaries should be checked (especially the
   "...httpd/cgi-bin" directory) for those that allow shell commands to
   be executed. Many attacks in recent months have focused on the use of
   utilities such as "phf" for accessing /etc/passwd on a target system.
   Remove any script that is not needed in the course of operation of a
   web server.

Other Suggestions

   * Check with the vendor of the operating system for known security
     issues. Make certain that all systems have the latest version of
     software--especially security patches to fix specific problems.

   * Examine log files on the host frequently. On Unix systems, the
     "last" command will furnish information on recent logins and where
     they came from. The "syslogs" or "Event Viewer" will contain more
     specific information on system events.







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RFC 2179            Network Security For Trade Shows           July 1997


   * Web server logfiles (...httpd/log/access_log and
     ...httpd/log/error_log) will contain information on who has been
     accessing a WWW server, what has been accessed, and what has
     failed.

   * Good backups are the best defense against system damage. Perform
     backups before placing a system on the trade show network then
     continue backups throughout the show and again following the event.
     A final backup set is useful to examine for possible attempts at
     (or successful) penetrations of system security.

General Network Security

   As would be expected at network trade shows (large or otherwise),
   there are many entities running packet sniffers. Most are exhibitors
   who have a legitimate need to run them during the course of product
   demonstrations. However, be aware that there are many "listening
   ears" on network segments--any of whom can "hear" or "see"
   information as it crosses the net. Particularly prone to
   eavesdropping are telnet sessions. A good rule of thumb is to assume
   that "when you type your password, the only one that doesn't see it
   is you!"

   It is a good practice to not log in (or "su") to an account with
   privileges across the network if at all possible. As mentioned
   previously, authentication tokens and ssh are a simple way to add
   security to system account access.

Packet Filtering

   Many routers support basic packet filtering.  If a router can be
   deployed between the local network and the show's network, general
   basic packet filtering should be employed.  Below is a good "general"
   packet filter approach. The approach itself is ordered into
   categories:

   * General global denials/acceptance.
   * Specific global service denials.
   * Specific service acceptance.
   * Final denial of all other TCP/UDP services.

   Based on the theory of denying everything that you don't know is
   acceptable traffic, a good approach to a filter ruleset, in order of
   execution priority, might be:







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RFC 2179            Network Security For Trade Shows           July 1997


   General Global Denials/Acceptance

   1 Filter spoofed source addresses by interface. Match source
     addresses to routing information available for the interface.
     Discard packets with source addresses arriving on one interface
     (from the "outside" for example) claiming a source address on
     another interface (the "inside").
   2 Filter all source routed packets unless source routing is
     specifically needed.
   3 Allow outbound connections from "inside" hosts.
   4 Allow established TCP connections (protocol field contains 6 and
     the TCP flags field either contains ACK or does NOT contain SYN
     bit). Only filter requests for 'new' connections.
   5 Filter 'new' connections with source port of 25. Prevents people
     from pretending to be a remote mail server.
   6 Filter loopback address (source address 127.0.0.1). Prevents
     packets from a misconfigured DNS resolver.

   Specific Global Service Denials

   1 Specifically block all "R-command" ports
     (destination ports 512-515).
   2 Block telnet (destination port 23) from any host not requiring
     telnet access from the outside. (If you use ssh, you can
     block it from all hosts!)
   3 Add specific filters to deny other specific protocols to the
     network, as needed.

   Specific Host/Service Acceptance

   1 Add specific access to specific "public" hosts' services
     (unsecure FTP or WWW servers).
   2 Allow SMTP (source and destination port 25) for electronic mail
     to the mail server(s).
   3 Allow inbound FTP connections (source port 20) to the FTP server(s).
   4 Allow DNS (source and destination port 53, UDP & TCP) to name servers.
     If zone transfers are not needed, block the TCP ports.
   5 Allow RIP packets in (source and destination port 520, UDP), if
     appropriate.
   6 Add specific filters to allow other desired specific protocols
     or to open certain ports to specific machines.

   Final Service Denial

   1 Deny all other UDP and TCP services not allowed by the previous
     filters.





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Author's Address

   R. Allen Gwinn, Jr.
   Associate Director, Computing
   Business Information Center
   Southern Methodist University
   Dallas, TX  75275

   Phone:  [phone]
   EMail:  [e-mail]  or  [e-mail]


Contributing Writer

   Stephen S. Hultquist
   President
   Worldwide Solutions, Inc.
   4450 Arapahoe Ave., Suite 100
   Boulder, CO  80303

   Phone: [phone]
   EMail: [e-mail]





























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