Re: keeping ports open
From: Karl Levinson [x y] mvp (jamescagney90210@excite.com)
Date: 11/03/02
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From: "Karl Levinson [x y] mvp" <jamescagney90210@excite.com> Date: Sun, 3 Nov 2002 07:59:22 -0500
"FA" <farefin@fastmail.fm> wrote in message
news:484e01c28317$65f3acf0$36ef2ecf@tkmsftngxa12...
> 1. Is there any risk of keeping ports above 1024 open
> (provided there is no trojan on the computer)?
>
> 2. Suppose a port below 1025, say port 23 (telnet) of a
> user's computer is open, what are the treats the user is
> exposed to from a hacker?
If a port is open, it means that 1) a software or service is running on your
computer [such as the Telnet service] and listening for incoming requests on
that port, and 2) you're not using a firewall or your firewall isn't
blocking incoming requests.
It's good security to use a firewall and disable all services that you're
not planning on using. The firewall should block all ports that you don't
plan on using or that are dangerous, both inbound from and outbound to the
internet.
Other than that, there's no way to answer your question without knowing
which port you're talking about. Different ports have different levels of
danger. If you need to keep, say TCP port 23 open, then you usually assess
the risk and take additional steps to reduce the risk, such as installing
all security patches, allowing that port to be open only from certain
approved IP addresses via your firewall, or using VPN or other encryption.
The risk of keeping any port open is that any port can be used by a trojan
or hacker.
For any computer on the internet, I think you really want to consider
following the standard procedures to secure a computer:
=============
How can I harden my computer or server to secure it from hackers?
A: [Note that if you have already been hacked, this section will not help
you re-secure your computer. In this case, you should first read the section
in this FAQ entitled "How can I re-secure my computer or server after being
hacked?"]
Here is the short answer:
1. Do not put the computer onto the network or the Internet until after the
computer has been hardened using the instructions below [or at least not
before a firewall and antivirus have been installed].
2. Use firewall software and hardware and antivirus software that is
configured to download updates every day;
3. Follow the instructions for hardening Windows and IIS at
www.microsoft.com/technet/security ;
4. Install all service packs and security fixes from Microsoft and otherwise
for all Microsoft software on your computer [Windows, IIS, Office, Internet
Explorer, Windows Media Player, etc.] from
www.microsoft.com/technet/security ;
5. [Ongoing] Download MBSA from www.microsoft.com/download and run it now
and also at regular intervals to look for vulnerabilities in your settings,
new patches that are missing, etc. Also, check your antivirus to confirm
that the last successful update was less than 14 days ago.
These steps will make your computer fairly secure, but may still leave some
holes. Keep reading below for additional information you should be aware of:
A successful hacker, virus or worm intrusion into one of your computers can
drain your free disk space, slow down your Internet connection, compromise
your credit card numbers, damage your personal documents, allow intruders to
access other machines on your network that DO contain important files,
and/or leave you legally liable for other government or business computers
on the Internet that are hacked by an intruder using your computer. This is
why you should consider securing ALL the computer systems in your home or
network, even if you think there is nothing important on the computer or it
is "just a test computer."
All Windows users should seriously consider all of the procedures below to
help prevent intrusions on their computers:
1. Do not put the computer onto the network or the Internet until after the
computer has been hardened using the instructions below. [Un-secured
computers can be hacked in just 15 minutes or less after being put onto the
Internet.] Depending on your environment, it may be acceptable to put your
computer on the Internet after installing a firewall and antivirus software
with the latest updates.
2. Seriously consider enabling or installing firewall software and/or
firewall hardware. There are a number of free firewalls available, including
the ICF feature that comes with Windows XP [unless XP is joined to a Windows
domain], and/or other third-party firewalls available on the Internet.
For more information on how and where to locate free and not-free firewall
software and hardware, see the section in this FAQ entitled "Which firewall
should I choose? Which firewall is the best?"
3. Seriously consider installing an antivirus program and configure it to
automatically download updates daily.
For more information on where and how to locate and use free and not-free
antivirus software, see the sections in this FAQ entitled "Which antivirus
should I choose? Which antivirus is the best?" and the section entitled "I
think I might have a virus / worm / Trojan."
4. Follow the instructions for hardening Windows 2000 and also IIS [if IIS
is installed] at www.microsoft.com/technet/security [For Windows 2000 / NT,
hardening IIS usually includes installing IISlockdown including URLScan. For
computers with FTP service installed, it usually includes removing the Posix
subsystem and removing write permission from the anonymous user account,
among other things.]
5. Download and install all the service packs and security patches from
www.microsoft.com/technet/security for all the Microsoft and non-Microsoft
software installed on your computer, especially Microsoft Windows, Office,
Internet Explorer, Outlook Express, Windows Media Player and IIS [if IIS is
installed].
Note that Windows 2000, XP, .NET and NT users should also download patches
for Indexing Services a.k.a. Index Server. Do not assume that Index Server
patches are included with any IIS comprehensive service pack rollup you may
already have installed, because they are not.
[If you want a shortcut to do this faster, you could try this:
* Download and install the latest Windows service pack from
www.microsoft.com/technet/security;
* Reboot and visit http://windowsupdate.microsoft.com to receive additional
patches;
* Reboot, download and run MBSA [Microsoft Baseline Security Analyzer] or
HFNETCHK from www.microsoft.com/download to discover other missing patches;
* Manually download from www.microsoft.com/technet/security and install any
patches that were found to be missing, as well as patches for any server
products that may not be included in Windows Update and MBSA/HFNETCHK, such
as possibly SQL Server, ISA Server, etc.
* NOTE however that Windows Update, MBSA and HFNETCHK do NOT necessarily
list all Microsoft patches or search all Microsoft products, so you could be
missing some patches if you rely just on these tools.]
6. [ONGOING] Re-run the MBSA tool from www.microsoft.com/download every 60
days or sooner to look for missing patches, and confirm that your antivirus
program received an update in the past 10 days or less.
If you want or need even more security [or are particularly paranoid or at
risk], you can consider some of the additional steps below. Some of the
tools below may be more security than you need, unless you are running a
server such as IIS web or FTP services.
* Download and install MyNetWatchman or Dshield. These are free programs
that work with your firewall software or hardware to automatically report
hacking attempts to the hacker's ISP. You get to see information about
whether that IP address has been used to scan or hack other computers, or
whether it might be targeting just your computer. You also get to see
whether the ISP has responded or taken action against the offending user.
This is highly recommended. You can get this software at one of the links
below:
www.mynetwatchman.com
www.dshield.org
* Sign up for the Microsoft security mailing list at
www.microsoft.com/technet/security to receive emails with a link to new
critical security patches as they are released, and install them ASAP.
* Use Fport or Vision from www.foundstone.com/knowledge or pslist / pstools
from www.sysinternals.com to look at the open ports on your computer and the
program or executable using that port. Some firewall software such as
www.sygate.com will also tell you this information.
You can also use the NETSTAT -A command that comes with Windows to look at
open ports; however, this will not identify which program is using the port.
[You may want to run a command such as FPORT >> C:\OPENPORTS.TXT or
PSLIST >> C:\OPENPORTS.TXT or NETSTAT -A >> C:\OPENPORTS.TXT
This command will create a "baseline" text file named c:\openports.txt that
can be compared later with the results of the command to tell you whether
additional ports are now open, a possible sign of intrusion.]
* Consider running one or more vulnerability scanners to look for security
flaws and configuration errors on your computers. Vulnerability scanners
should be run after you have installed and hardened a new computer or
server, and also run at regular intervals to confirm that your computers are
still secure. You might also run a port scanner against your computers as
well to look for open ports.
See the section in this FAQ entitled "How can I scan my computer or firewall
to look for open ports or confirm that my machine is secure?" for more
information.
* Consider searching for and following additional checklists for hardening
Windows 2000 by searching an Internet search engine such as www.google.com
for words such as "harden OR hardening windows-2000" [e.g.
www.google.com/search?q=harden+OR+hardening+windows-2000 ]. Several such
checklists are available at http://nsa1.www.conxion.com/win2k/download.htm
a.k.a. http://www.nsa.gov, as well as www.labmice.net/security,
http://rr.sans.org, etc.
* Uninstall any unnecessary Windows components [e.g. click on Start,
Settings, Control Panel, Add/Remove Programs, Add/Remove Windows
Components]. Pay particular attention to Indexing Service, Internet
Information Services (IIS), Management and Monitoring Tools, Message Queuing
Services, Networking Services, Other Networking File and Print Services,
Outlook Express, and Windows Media Player. If you are not sure whether
something is unnecessary, try searching www.google.com or posting a question
to the appropriate Microsoft security newsgroup.
* Disable any unnecessary Windows services [e.g. click on Start, Settings,
Control Panel, Administrative Tools, Services]. If you are not sure whether
something is unnecessary, try searching www.google.com or posting a question
to the appropriate Microsoft security newsgroup.
* Consider using a Trojan scanner. Antivirus programs generally detect some
but not all of the most common Trojans and hacker tools. Some people choose
to use a Trojan scanner in addition to antivirus.
For more information on where and how to locate and use free and not-free
Trojan scanner software, see the section in this FAQ entitled "Which
antivirus should I choose? Which antivirus is the best?"
* Enable logging. Most logging is disabled by default, and usually this is
not discovered until after an intrusion, when the logs are needed.
Enable logging of your IIS web server, FTP server, etc. For sites with a
small number of hits, consider changing logs to rotate monthly instead of
daily to allow easier searching of logs.
Enable logging on your Internet router, switch or firewall. [Because these
devices usually do not have much storage space for saving logs, doing this
may involve installing free syslog software onto your computer to be able to
capture the logs.]
Enable auditing of security events on your Windows system, including logon
successes and/or failures and NTFS auditing of files and registry keys. For
more information, see the section in this FAQ entitled "How can I enable
auditing / logging on my computer / server?"
Change the Windows event log settings to be appropriate for your
environment. Consider increasing the maximum log size to retain more
information. Be careful not to log too much, or you might find that your
logs contain only a few minutes or hours worth of data.
Check the logs to be sure logs are really being captured.
* Consider using a file change checker, such as the unsupported free tool
Languard File Integrity Checker at www.gfi.com/languard/lantools-fic.htm
Files changing on your system can sometimes indicate a hacker intrusion.
* Consider using a Windows event log monitor. Some types of intrusions leave
entries in one of the logs on your computer. [On an especially vulnerable or
secure system, you should be sure that you've configured logging to detect
events such as intrusions.] Some network monitors such as www.ipsentry.com
can send a message to your email/screen/pager if a server or service stops
responding, an event or error appears in a Windows log, etc. Windows log
monitors can be found by searching an Internet search engine or your
favorite software web site, or by using the links below:
www.ipsentry.com [around $100 US]
www.sunbelt-software.com
www.webattack.com
www.wilders.org
www.download.com
www.tucows.com
www.google.com/search?q=windows+event+log-monitor
* Consider using EFS file encryption [under Windows 2000 / XP / .NET] or
third-party utilities to encrypt the files on your computer may be something
to consider. Some of these utilities can encrypt your entire hard drive
including Windows, whereas other tools just encrypt some of your data files
and are not suitable for encrypting or preventing access to Windows.
Note that using any form of encryption can slow down your computer's
performance. Also, you must be extremely careful to back up and protect your
encryption key and any passwords. If the encryption keys are not backed up,
users can lose their encrypted files forever when Windows is reinstalled,
Windows encounters a problem so that Windows no longer starts up, etc.
For more information on EFS file encryption on Windows 2000 / XP / .NET, see
the section in this FAQ entitled "I used Windows 2000 / XP EFS file
encryption to encrypt some files. Now, I can't read the files. How can I
unencrypt them or recover the key?"
Third party encryption software can be found at the following locations:
www.pgp.com
www.scramdisk.clara.net
www.e4m.net
www.jetico.com ["BestCrypt"]
www.download.com
www.tucows.com
www.google.com
====================
Which firewall should I choose? Which firewall is the best?
A: The answer to this question varies depending on your computer systems,
your security requirements and your personal preferences. Below are some
firewalls and other forms of firewall-like packet filtering:
NO MATTER WHICH FIREWALL YOU CHOOSE...
No matter which firewall you choose, you should seriously consider
downloading and installing MyNetWatchman or Dshield. These are free programs
that work with your firewall software or hardware to automatically report
hacking attempts to the hacker's ISP. You get to see information about
whether that IP address has been used to scan or hack other computers, or
whether it might be targeting just your computer. You also get to see
whether the ISP has responded or taken action against the offending user.
You can get this software at one of the links below:
www.mynetwatchman.com
www.dshield.org
Also, no matter which firewall you choose, the lists below of port numbers
for common software services may be helpful when configuring your firewall
or when trying to monitor the firewall logs for signs of intrusion:
www.iana.org/assignments/port-numbers
www.iisfaq.com/default.asp?View=P106
FIREWALL SOFTWARE:
www.sygate.com [free for non-commercial use, also works like a sniffer]
www.kerio.com [free for non-commercial use]
www.agnitum.com [free for non-commercial use]
www.zonealarm.com [free for non-commercial use, also blocks pop-ups]
www.iss.net [Black Ice]
www.symantec.com [Norton]
www.webattack.com
www.download.com
www.tucows.com
[Windows XP users can also consider using the ICF firewall that comes with
XP, more info below]
FIREWALL DEVICES [HOME / SOHO]:
www.linksys.com [starts around $70 US]
www.netgear.com [starts around $70 US]
http://search.ebay.com/search/search.dll?query=firewall [prices on new and
used firewalls]
________________________________________________________
Which antivirus should I choose?
Which antivirus software is best for you will vary depending on your
computer systems, your security requirements and your personal preferences.
Antivirus programs may be purchased from Internet web sites, from your local
computer store, and even from stores like Target and Wal-Mart. Antivirus
software can be found using the links below:
www.symantec.com [Norton Antivirus]
www.grisoft.com [AVG Antivirus [including a free version]
www.f-prot.com/products [free DOS version]
www.f-secure.com [F-Secure]
www.trendmicro.com [Trend Micro]
www.wilders.org
www.download.com
www.tucows.com
[Most of the antivirus products will also work on Windows Server products or
have a version for Windows Server.]
There are also a number of web sites that will scan your computer for
viruses for free. However, using these web sites will do nothing to protect
you against future re-infection and damage to your computer files. Some of
these web sites include:
http://security2.norton.com [Norton free one-time web-based scanner]
http://housecall.antivirus.com [Trend Micro free one-time web-based scanner]
Just running an antivirus program is not enough. You should make sure that
your antivirus program can be configured to download updates every day [or
every week] automatically via the Internet, and open the program from time
to time to ensure that it is still receiving updates.
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