Computer and Network Policy (IT Security Cookbook)

The administrator ensures that the systems are available when needed, that confidential information is only available to those authorised access and that the information is not subject to unauthorised changes.

The following need to be defined:

  • Who/where updates administration policies?
  • Who is authorised to grant access and approve usage? Who may have system administrator privileges1)?
  • What are the rights and responsibilities of an administrator?
  • Are users to be allowed root/administrator access to their workstations?
  • The current directory should never be in the directory search path for administrative users (prevention of trojan horses).

1.1.Physical security

A Physical Security policy document should exist detailing the measures taken to protect buildings as regards disasters (flooding, fire, earthquakes, explosions, power outage), theft, access control, safes, computer rooms & wiring cabinets. (see also Physical Security chapter).

  • Zones should be defined, for example:
    • Zone 1: Areas open to the public.
    • Zone 2: Areas not open to the public, open to company staff.
    • Zone 3: Protected areas. Only accessible with identification, access strictly controlled.
  • Who is responsible for destruction of defective confidential disks & tapes?
  • Who is responsible for destruction of old servers/disks/tapes? May they be repaired?
  • Define directives for server rooms (zone 3):
    • All computing devices should be cleanly installed and labelled.
    • Wiring should be neat, labelled and such that connections may not be accidentally disturbed/broken.
    • A diagram of what server are installed where should be available, along with contact persons.
  • Define directives for the transport of electronic media (tapes, backups, disks…).

1.2.Access Control

  • All users should be authorised.
  • Users should be able to set the privileges of objects belonging to them in their environment.
  • Users should be prevented from deleting others user's files in shared directories2).
  • Consider allowing root login only via the console (for class 33)).
  • It should be possible to control user access to all objects on the system (files, printers, devices, databases, commands, applications etc.) according to a stated policy (for class 3).
  • Users should not be able to examine the Access Control granted to other users (for class 3).
  • It should be possible to label data with a classification 1 to 4 (for class 4).
  • Mandatory access control should be provided (for class 4).

1.3.Logon Policy

Basic principle:

  • Give a User the minimum privileges for the shortest time necessary to do their work.
  • Accounts should only exist for authorised persons.
  • Each user must be identified by a name or number and belong to a group (for class 2).
  • Username and group name structure should be standardised enterprise wide (number of characters, composition) if possible.
  • User and groups must be managed by the administrator (or equivalent), not by users themselves.
  • Group accounts are to be avoided (class 3 forbidden).
  • Each user should have only one account on the system (for class 3).
  • If guest accounts are used, their working environment should be very restricted (for class 2).
  • Guest accounts are not allowed.
  • Usernames and passwords should not be distributed in the same communication.
  • When a user is transferred or terminates employment, his account should be blocked or deleted immediately. Procedures should exist whereby the personnel administration automatically informs system administrators.
  • A screenlock should be activated after 15mins idle time with password protection.
  • The current directory should not be included in the users search path (for class 3).
  • User application & system configuration should only be writable by the user and not be world readable4).
  • The users file creation mask («umask» on UNIX) should not give world read or write access to new files created (for class 3).
  • Users should be informed of actions that violate security. Likewise they must inform their security administrator if they suspect a security violation.
  • If an account is subjected to continuous login failures in short period of time (e.g. 20 attempts in 1 hour), block the account and notify the user. Don't do this for administrative accounts (open a denial of service attack weakness) (for class 2).
  • When a user logs on the following should be displayed (for class 2):
    1. a legal notice informing the user of implications of system abuse.
    2. the time & device of last successful and unsuccessful login (user should check that they are correct).
  • Logons should only be enabled when necessary (e.g. between 06:00 and 22:00 Monday to Friday) (for class 2).
  • Avoid allowing direct superuser logon, especially where more than one person administers a system (for class 2).
  • On Dialup systems:
    1. disconnect the phone line after (say) 3 unsuccessful login attempts (for class 2).
    2. it should be possible to specify what ports are available at what time of day (for class 3).
  • If a user enters a bad login name or password, the error message should be the same for both cases. A possible attacker should not be informed if a user account is valid, rather that the combination of account and password is incorrect5)(for class 3).
  • If an incorrect username/password combination is entered, wait one second before presenting the login prompt again. If the combination is again incorrect, wait 2 seconds, the next time 3 seconds etc. This should slow (& frustrate) attackers and especially automated logon-attack-programs6) (for class 3).
  • Members of the administrator groups should be authorised by management (for class 3).
  • It should be possible to specify how many simultaneous sessions a user may have (for class 3).
  • It should be possible to set an expiration date for a user account (for class 2).


  • Audits should be run regularly on the system (for class 2 once per year, fjr class 2 once every 3 months).
  • New servers are installed and prepared by their system administrator. Then they should be audited and certified to one of the sensitivity levels by security staff. If all directives cannot be implemented for a particular system (due to OS limitations for example), these exceptions must be clearly documented in the Certification.
  • Conformance of current operating systems to ITSEC/TCSEC requirements is discussed the Chapter «Operating Systems Overview».

1.5.Accountability and Audit (only class 3)

  • Audit trail logs and programs/utilities must be protected. They should only be accessible by security personnel.
  • Logs should not contain passwords.
  • System administrator activity (especially use of su in UNIX) should be logged.
  • Unsuccessful login attempts should be logged (and possibly notified).
  • Important events should raise an alarm (high priority message) automatically.
  • It should be possible to specify auditing on a per subject and per object basis.
  • Each entry in the audit log should contain at least: Username or UID, date & time, terminal id, error level (success or failure) and event description.
  • Logs should be kept on read-only media if possible (paper, WORM). Logs should also be forwarded to a specially secure machine instead of locally on each machine, if possible. Avoid storing logs on shared filesystems.
  • All machines should have their clocks synchronised to guarantee the validity of audit log timestamps.

1.6.Reliability of Service

Backup & Restore Policy

  • Backups should be made regularly and some backup media should be stored regularly off-site.
  • Class 3 backups should be stored in a locked safe. All media must be accounted for. Old tapes must be destroyed, not thrown away.
  • A backup policy must exist (documented) for each system or group of systems, containing:
    • When and how are (full or incremental) backups made, where are media stored, for how long?
    • How often are backups made, who is responsible for checking their correct operation?
    • How long are indices kept? Where are they stored? How can they be recovered from archive media?
  • A restore policy must also exist, containing:
    • Who is responsible for checking correct operation?
    • A detailed description of what utilities are used how to restore data for all applications. (e.g. OS, database restore mechanisms).
    • In particular a detailed description of how to restore the Operating System after serious disk or other hardware failures is required. Use of embedded EPROM commands, single user or diagnostic modes (where available) should be documented.
    • The expected restore time for various disaster scenarios should be documented
  • Test the restore policy regularly.

Change Management (sw/hw installations or updates)

  • Only system administrators should install or update software on servers. Users may not install software on class workstations.
  • Systems should be cleanly installed according to vendor instructions.
  • A change log, detailing all changes to a system should be kept on EVERY server. It is suggested that as a minimum, a simple text file be created (e.g. /etc/mods) containing: Date, sysadmin name, files changed and reason/comment.
  • OS installations should include installation of all recommended patches.
  • A label containing the following information should be stuck on all machines during installation: Hostname, Machine manufacturer/model, IP address, MAC address, cabling node id (if network topology allows), end of guarantee date and security/helpline telephone number.
  • Servers should also have: the server name on all peripherals, disk type/guarantee date/superblocks/configuration, console commands for stopping/rebooting (e.g. special key sequences)
  • Only patches from the original sw vendor should be applied. Patches downloaded from public networks (e.g. Internet) should be checked for integrity using a strong hashing mechanism (e.g. MD5). Patches should be pre-tested in a test environment (for at least a few weeks if possible) before being applied to production systems.

Transmitting information between computers can pose a significant threat to security.

2.1.Network / Distributed Systems Policy

1. Assurance: Network configuration shall be documented.

2.Identification and Authentication:

  • It should be possible to identify and authenticate any subject on the corporate network.
  • If possible, a single mechanism should be available to log-on users across multiple applications and systems, therefore avoiding multiple usernames and passwords.

3.Accountability and Audit

  • Users are accountable for their actions. They must observe the «Network User Policy».
  • Important network nodes should log activity. These logs should be regularly analysed for security breaches.
  • The Access Control Lists of important filters shall be audited every 6 months.

4.Access Control

  • Configuration of sensitive Network nodes: Unnecessary network services shall be disabled. Network services shall be configured restrictively and have all security bug fixes (patches) installed.
  • Available networks could be labelled open access, restricted access or highly restricted access, so that users/data owners are aware of the protection offered. For example if a LAN is labelled open access and confidential information needs to be transmitted over this LAN, then additional measures such as application level encryption will be necessary to make up for the deficiency on LAN security. Token ring and FDDI are examples of restricted access networks (if correctly managed).
  • Where restricted access networks are required, cabling should not be passed through public areas, it should be protected in conduit and connection points should be only be available to authorised persons. :*If the cabling is installed by externals, inspect it.

5.Accuracy: Important network nodes should check the integrity of their data regularly.

6.Data Exchange:

  • Confidential information shall only be transmitted by approved transport mechanisms (e.g. Email systems used for confidential data shall be approved by security management).
  • Login session information (e.g. username, password) should not be sent over the network in clear form.
  • Inter-host network services should authenticate each other.
  • Networks shall be protected against information eavesdropping ⇒ Network sniffers such as snoop, etherfind, tcpdump, iptrace etc. shall not be available to users. Networks shall be divided up into subnets, active bridges and hubs shall be used and unused network connection points shall be disabled.
    • Encryption of Class 3 data before transmission on internal networks should be considered. Class 3 data transmitted over public networks must be encrypted.
    • If possible networks should be protected against electromagnetic eavesdropping (for class 3).
  • When information is being transmitted (sent or received), the sender's or receivers identity must be attached to the information and checked by the various components responsible for the transmission.
  • Class 3 data should not be sent to unauthorised users or to systems with a lower classification.
  • In certain applications (e.g. class 3 email), mechanisms should exist for proving that sender / receiver did actually transmit / receive that data. (Proof of origin / receipt).

7.Reliability of Service / Availability

  • The network is required 24 hours, 7 days a week. Maintenance window Wednesday 18:00-22:00. Maximum down time during office hours shall be 1 hour, maximum frequency once every two months.
  • The network shall be monitored for errors and performance problems. Preventative action should be taken before serious network disruptions occur, where possible.
  • Change management: Updates and configuration changes shall be logged and carried out according to Quality processes.
  • A label containing the following information shall be stuck on all nodes during installation: Hostname, Machine manufacturer/model, IP address, MAC address, cabling node id (if network topology allows), end of guarantee date and security/helpdesk telephone number.

Remote Access Policy: external network interfaces

Networks (X.25, Dial-up, Internet, Vendor networks, Telephone networks, Customer networks etc.) shall not be interconnected if it results in breach of the security policy. Access to external networks must occur over a Firewall. The Firewall must have a security policy and be regularly monitor and audited.

2.2.Dial-in access

All incoming Dialup connections (via PSTN or ISDN) should use a strong one-time password authentication system (such as Secur ID).

Dial-in access to the corporate network should only be allowed where necessary and where the following conditions are met:


  • The dial-in server configuration shall be accurately documented.
  • It shall be subjected to yearly audits.

2.Identification and Authentication

  • All incoming Dialup connections (via PSTN or IDSN) shall use a strong authentication system: one-time passwords, challenge-response, etc.
  • Administrator login shall not send passwords in clear-text.
  • In addition, the call-back or closed user groups features should be used, where possible.

3.Accountability and audit

  • Users shall be accountable for their actions.
  • Dial-up servers shall provide detailed logging and auditing of connections.
  • Logs shall be automatically analysed, with critical errors generating alarms.
  • Logs shall be archived for at least one year.
  • The non trivial log entries shall be examined daily.
  • Statistics on usage should be available.
  • The servers shall be subject to regular monitoring (weekly) and yearly audits.

4.Access Control

  • Dial-up servers shall not share file or printer resources with other internal machines, i.e. they shall not be file or printer servers.
  • Only administrative personnel shall be allowed to log on locally.
  • Users shall not be able to logon directly to these machines (from the inside).
  • Dial-up servers shall be installed in a physically secured (locked) room.
  • A list should be kept of those users with modems. If possible the telephone network should be regularly scanned for unauthorised modems.
  • Switch off modems at night if not needed (you can get a $5 timer to do this).

5.Accuracy: no requirements.

6.Data Exchange

  • Use encrypted password communication (e.g. encrypted Telnet, SSH) if possible, especially for remote administrator access.
  • Non repudiation of origin & receipt is not required.

7.Reliability of Service

  1. Dial-up servers shall have all unnecessary services stopped.
  2. Dial-up servers shall be a robust multitasking machines (e.g. UNIX, VAX or NT).
  3. Dial-up servers shall offer the following availability: ⇒ 7x24h, maximum downtime 4 hours (during office hours), maximum frequency twice per month. Maintenance window: Wednesday evening after office hours.
  4. Change management: Updates and configuration changes shall be logged and carried out according to :#Quality processes.
  5. Alerts should be raised if important processes crash.
  6. Regular backups shall be made where necessary.

2.3.Dial-out (PSTN/ ISDN)

Dial-out network connections can extend the corporate network, creating uncontrolled points of access to the network.

1.Users shall not use dial-out capability (modems) on their machines.

2.If such functionality is required, it shall:

  • be authorised by the concerned line manager and corporate Security and the authorisation shall be reissued yearly.
  • take place via a centralised «dial-out» server regularly audited by corporate security.
  • be recorded on a list of those users with modems.
  • if possible, the telephone network should be regularly scanned for unauthorised modems.

2.4.Internet Firewall

The Internet is often an important tool for sharing and searching information, especially in a research environment. All Internet access from the corporate network must occur via a Firewall.


  • The firewall policy and configuration must be accurately documented.
  • The firewall machines must be subject to regular monitoring and yearly audits.

2.Identification and Authentication

  • Incoming user connections from the Internet shall use a strong authentication system: one-time passwords, challenge-response, etc..
  • Administrator accounts shall also use either a one time password mechanisms or encrypted login sessions.

3.Accountability and audit

  • Firewall and proxy machines shall be securely installed. All unnecessary services shall be stopped in the operating system.
  • Detailed firewall logs shall be kept (if possible on a dedicated server, with write-once media).
  • Logs of all security audits shall be kept.
  • Logs shall be automatically analysed, with critical errors generating alarms.
  • Logs shall be archived for at least on year.
  • The non trivial log entries shall be examined weekly.
  • Statistics on usage should be available.

4.Access Control

  • All Internet access from the corporate network must occur over proxies situated in a firewall.
  • Default configuration: unless otherwise specified, services are forbidden.
  • All users are allowed to exchange email with the Internet.
  • R&D department users are allowed to use WWW and ftp (over proxies). Other users require authorisation.
  • Users may not provide services to the Internet.
  • Research departments requiring full Internet access for experimental services should not install these services on the corporate network, but on a separate network outside the Firewall.
  • Users should not be able to logon directly onto Firewall machines.
  • Internet access to illicit material should be prevented where possible.


  • The firewall machines shall have the integrity of their files regularly (every month) checked.

6.Data Exchange

  • All login sessions to Firewall machines shall use encrypted login or one time passwords.
  • Subversion and spoofing of network services such as routing, DNS and email should be prevented.

7.Reliability of Service

  • The Firewall shall be available ⇒ 7x24h, maximum downtime 4 hours (during office hours), maximum frequency twice per month. Maintenance slot: Wednesday after 18:00.
  • Change management: Updates and configuration changes shall be logged and carried out according to Quality processes.
  • Alerts should be raised if important services/processes crash.
  • Important services (such as WWW proxy) should be configured for high availability.
  • Regular backups shall be made where necessary (e.g. configuration files, changing data such as WWW).

2.5.Interfaces to other networks

Likewise interfaces to other networks (SNA, Decnet, X.25, ATM etc.) required a clear policy.

Interfaces to customer/vendor networks

Access from customer or vendor sites to the corporate networks are more and more common.

  • A policy document should exist for each such interface outlining what information is to be transferred, how and how this relates to the corporate security policy.
  • Such interfaces must be protected by a Firewall and be subject to regular monitoring and auditing. (see above).
  • A Service level agreement shall exist which ensure that the interface conforms to Network policy.
  • A non disclosure agreement should be signed by the customer/vendor, ensuring that neither details of the interface, nor data accessible via the interface may be disclosed to third parties.

Telephone networks

Phone, Fax and Voicemail systems and networks are frequent penetration points for attackers. If these system have features accessible from the outside, a policy is required to prevent abuse.

2.6.Incident Response Procedure


This procedure should detail which actions should be taken in case of a security incident on the Firewall. The Firewall is designed to protect the corporate network from unauthorised Internet access. It is regularly monitored for security breaches. When a breach is detected, one must know how to react. That is the aim of this procedure. The reaction to an incident aims to protect and restore the normal operating condition of computers, services and information

  • Legal aspects are not covered in this document. They may be covered in a later version.


Even with a solid security policy, educated users and solid system administration, an emergency response team is useful. Plan for a disaster!

  • Who is on «Firecall», how should they react to a serious security breach?
  • If internal personnel are not expert enough, a «emergency standby» contract could be outsourced to a specialised company.
  • Decide in advance who will be in charge in the event of a security incident. Determine the chain of command (define processes & responsibility).

Incident Response Team

The principal roles are indicated in italics below. For each role a backup person should be available.

Management Responsible A.Boss, (Tel. xxxx),

(Overall co-ordinator/responsible) backup: B. Other_Boss (Tel. xxxx).

Responsibility: Ensures that this document exists and is enforced. Recognising the major threats to business continuity. Prioritises activities, co-ordinates and makes key decisions during an incident. Approves exceptions to this procedure.

Technical Responsible Firewall A. Techie (Tel. xxxx),

backup B. Other_Techie (Tel. Xxx).

Responsibility: Knows how to technically administer the systems in question. Can detect incidents and can take technical measures to limit damage. A good technical understanding of the system is essential.

Press Responsible A. Prman (tel. Xxx),

backup: A. Other_PrMan (Tel. Xxx).

Responsibility: Handles interfaces to the media, public statements, co-ordinate communications. Additional Help:

Legal Advice ?

First Response Team, See appendices.


1.In case of an emergency, each of the following points should be considered and acted upon. The principal steps involved are:

  1. Preparation: The team should have read this chapter and be aware of the implications.
  2. Incident detection: quick assessment
  3. Immediate action: limit damage
  4. Public Relations / Communications
  5. Detailed situation analysis
  6. Recovery: restore data/services/systems
  7. Follow-up

2. Incident detection: quick assessment

What has happened? :

  • Source of threat: e.g. Accidental administrator damage/mistakes, accidental disclosure of internal or confidential documents, attack from the Internet, attack from the telephone network, attack from inside the corporate network or a hoax.
  • Result of threat: Integrity, confidentiality or availability of systems/services/data may have been affected.

If an attack has occurred:

  • Has the attacker successfully penetrated the systems. Can he re-enter at will? Where have intruders been detected? What is the extent of the damage? What is the principal danger posed? e.g. availability, information privacy, information integrity, adverse publicity.
  • Note that «obvious» attacks from one source may, in fact, hide a much more subtle attack from a different source.

3. Immediate action: limit damage: If a serious attack or disaster occurs, the Management Responsible and Technical Responsible should decide on the immediate action necessary to eliminate the threat or limit damage (depending on the gravity of the situation and user's needs).

⇒ It should be clear who is in charge of handling the incident in question. Define who is the overall responsible/ co-ordinator. Ensure that the chain of command is understood

⇒ Start an event log: Document every single action taken, events, evidence found (with time & date).

Possible immediate actions are:

  • a restore of information,
  • the concerned machine can be isolated from the network, or shutdown,
  • the corporate network can be disconnected from the Internet,
  • one or more Remote Access servers can be removed from the network, switched off or shutdown,
  • the network or computers are not switched off, but attempts are made to minimise the damage without :*affecting user services (this may be a risky approach),
  • an immediate copy of all logs/data could be made to tape or other offline storage.

4. Public Relations / Communications

  • Only the Press Responsible may contact or make statements to the press/reporters.
  • If details of an attack need to be discussed with anyone via email, use encrypted email with signatures (e.g. via PGP).
  • If deemed necessary and if authorised by the Press Responsible, report the incident to a FIRST/CERT and/or other affected sites.
  • If the immediate action will affect services to users, inform helpdesk on what message to pass on to users.

5. Detailed situation analysis:

  • Set priorities, decide what to do.
  • Determine the extent of damage. E.g.
    • Analyse the system(s): what files have changed? What programs/accounts were added or modified? If modifications are found, check for these modifications on similar systems.
    • Try to confirm exactly what happened.
  • Notify administrators, management and law enforcement authorities as required.

6. Recovery: restore data/services/systems:

  • Depending on the incident, the following may be necessary:
  • Clean systems and restore data/programs/services.
  • Fix weaknesses found in the system.
  • Do not trust programs on compromised systems, compare with safe copies (e.g. OS on CDROM).

7. Follow-up

  • Have all services been restored?
  • Has the weakness used by the attacker been addressed? Has the cause been dealt with?
  • Do insurance or legal claims/procedures have to be filed?
  • Does this Incident Response Procedure need changing?
  • If changes to the Firewall are required, active the Firewall change procedure.

⇒ End of procedure.

Security should be an integral part of new systems. When functional requirements are designed, security requirements should be formulated corresponding to the sensitivity and availability of data to be handled by the system.

3.1.General Guidelines

  • Separate development and production environments and data.
  • Consider security to be an integral part of application development.
  • Test data should not contain confidential information.
  • Consider using a secured language (e.g. Java rather than C, Tainted Perl rather than Perl).
  • Consider having major new systems ITSEC approved (class 3).

3.2.Production Guidelines

  • What documentation is to delivered with an application? E.g. Operating, Installation, Administration, Security, User Manuals.
1) Who is allowed root access? On UNIX systems, it is preferable to use sudo (for example) to restrict root powers. On NT systems, user groups can be used to restrict administrative access.
2) UNIX: The sticky bit should be set on world writeable directories
4) On UNIX, this means .cshrc, .mailrc, .login, .profile, .netscape etc.
5) This is standard on UNIX systems, but not (yet) on NT.
6) On UNIX, every 5 unsuccessful login attempts, the prompt is delayed for a few seconds.
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