Basic Internet Technical Details
The Internet utilizes a set of networking protocols called TCP/IP. The applications
protocols that can be used with TCP/IP are described in a set of Internet
Engineering Task Force (IETF) RFCs (Request For Comment). These documents
describe the "standard" protocols and applications that have been developed to
support these protocols. Protocols provide a standard method for passing
messages. They define the message formats and how to handle error conditions.
Protocols are independent of vendor network hardware, this allows communication
between various networks with different hardware as long as they communicate
(understand) the same protocol. The following diagram provides a conceptual
layering diagram of the protocols.
TCP/IP : Transmission Control Protocol/Internet Protocol
TCP/IP is used to facilitate communication within a network of diverse hardware
technology. Information is broken into packets (usually in the range of 1-1500
characters long) to prevent monopolizing of the network. TCP is a transport level
protocol which allows a process on one computer to send data to a process on
another computer. It is a connection oriented
protocol which means that a path must be
established between the two computers. IP
defines the datagram, the format of the data
being transferred throughout the network and
performs connectionless delivery.
Connectionless delivery requires each
datagram to contain the source and destination
address and each datagram is processed
separately. TCP takes the information, and
breaks it into pieces called packets, numbers
the packets, and then sends them.
The receiving computer collects the packets,
takes out the data and puts them in the proper
order. If something is missing, the receiving
computer asks the sender to retransmit. The packet sent also contains a checksum
which is used to find errors that may have occurred during transmission. If the
receiving computer notices that an error has occurred when it computes and
compares the checksum, it throws that packet away and asks for a retransmission.
Once everything is received, the data is passed to the proper application (e.g. email).
UDP:User Datagram Protocol
The UDP has less overhead and is simpler than TCP. The concept is basically the
same except that UDP is not concerned about lost packets or keeping things in
order. It is used for short messages. If it does not receive a response, it just resends
the request. Thjs type of protocol transfer method is called a “connectionless
protocol.”
Internet Addressing
All computers on the Internet must have a distinct network address to be able to
efficiently communicate with each other. The addressing scheme used within the
Internet is a 32 - bit address segmented into a hierarchical structure. IP addresses
consist of four numbers, each less than 256 which are separated by periods.
(#.#.#.#) At the lowest level, computers communicate with each other using a
hardware address (on LANs, this is called the Medium Access Control or MAC
address). Computer users, however, deal with 2 higher levels of abstraction in order
to help visualize and remember computers within the network. The first level of
abstraction is the IP address of the computer (e.g. 131.136.196.2) and the second
level is the human readable form of this address (e.g. manitou.cse.dnd.ca). This
address scheme is currently under review as the address space is running out.
Address Resolution Protocol (ARP) can be used by the computer to resolve IP
addresses into the corresponding hardware addresses.
Types of Connections and Connectors
There are two types of computer hosts connected to the Internet: server hosts and
client hosts. The server host can be described as an “information provider”. This
type of host contains some type of resource or data which is available to other hosts
on the Internet. The second type of host connected to the Internet is the client host
which can be described as an “information retriever”. The client host will access
resources and data located on the server hosts, but usually will not provide any
resources back to the server host.
Both server and client host computers can be connected to the Internet by various
methods that offer different communication capabilities dependent on varied
communications surcharges.
Direct Internet Connections: A computer connected directly to the Internet via a
network interface will allow the user the highest internetwork functionality. Each
computer connected in this manner must also have a unique Internet (IP) address.
This type of connection is also the most expensive.
Serial Internet Connections: Another type of connection offering most
communications capabilities is a SLIP (Serial Line Internet Protocol) or PPP (Point
to Point Protocol) connection. These two connection schemes offer similar services:
full network and application capability over a serial (modem) line. Since this
connection offers full TCP/IP and ICMP functionality each computer configured in
this manner requires its own IP address. This type of connection is an on-demand
service, at slower speeds, that therefore reduces communications charges, however
all TCP/IP and Internet vulnerabilities remain when the connection is "live".
An important point for the network security investigator to remember is that most
dial-up TCP connections, either SLIP or PPP, assign the IP address to a connected
machine dynamically. This means that when a system dials-up to the Internet
Service Provider (ISP), the ISP assigns an IP address at that point. It also means
that the address for the dialer may change each and every time the system
connects. This can cause serious problems for the investigator when attempting to
trace access back through firewall and router logs for specific IP addresses. You will
need to work closely with the victim and the ISP to properly track which system was
assigned a particular IP address when the system connected to the ISP at a
particular point in time.
Host Access Connections: The most limited type of network access is available as a
user account on a host which is directly connected to the Internet. The user will then
use a terminal to access that host using a standard serial connection. This type of
connection is usually the most inexpensive form of access.
Sneaker-Net Connections: This type of connection is by far the most limiting, since
the computer has no electrical connection to the Internet at all. This type of
connection is the most secure because there is no direct access to the user's
computer by a hacker. If information and programs are required on the computer
they must be transferred from a networked computer to the user's computer via
magnetic media or manually.
All computers with direct, SLIP, and PPP connections must have their own IP
address, and their security administrators must be aware of the vulnerability
concerns associated with these connections. Communications channels work both
ways: a user having access to the Internet implies that the Internet also has access
to that user. Therefore, these computers must be protected and secured to ensure
the Internet has limited access. A terminal user calling using an Internet host has
fewer concerns since the host is where the Internet interface lies. In this situation
the host must take all necessary security precautions.
To connect the various sub-networks and pieces of the Internet together, hardware
equipment is required. The following are definitions of the various terms which are
use to describe this equipment.
Repeater A repeater is a hardware device which is used to connect
two Local Area Segments that use the same physical level
protocol. The repeater will copy all bits from one network
segment to another network segment. This device will not
make any routing decisions at all, and will not modify the
packets. This device operates at layer 1 (Physical) of the
OSI Network Model. A repeater may also be used to
connect specific workstations in a physically local area to
each other. All units connected to a repeater “see” each
other’s traffic on the network. Repeaters are very often
used on networks like Ethernet/802.3 networks and very
commonly available at most computer stores at a low price.
Modem A modem is a device which will convert between the digital
signal structures that computers require and the analog
voltage levels that are used by telephone services. The
term MODEM stands for MOdulator DEModulator. A
modem operates at level 1 (Physical) of the OSI Network
Model and therefore does not modify the data packets or
make any routing decisions. Modems are used to connect
two computers together over standard phone lines (usually
for on-demand services). Current MODEM speeds range
from 50 bits per second to over 56 thousand bits per
second (56kbps).
Bridge A bridge is a device which is used to connect two Local
Area Networks that use the same LAN framing protocol
(such as Ethernet or token ring). The bridge acts as an
address filter by picking up packets from one LAN segment
and transferring them to another IF the bridge recognizes
that the packets need to travel from one LAN to the other.
If the communicating source system and destination system
are on the same side of the bridge, the bridge will not
forward the frame to the other side of the bridge.. The
bridge makes no modification to any packets it forwards,
and the bridge operates at layer 2 (data-link) of the OSI
Network Model.
Router A router is a device that is used to connect two or more
LAN, MAN or WANsegments that may or may not use the
framing protocols. Since the router operates at level 3
(Network) of the OSI Network Model it is able to make
routing decisions based on the destination network address
(IP address for the Internet). Routers will sometimes have
filtering capability included. In this case a router might be
used as a packet filter to enhance security and/or reduce
traffic flow throughout the network that does not need to
traverse all locations on the network (described below).
Some very large routers at larger network sites can
interconnect dozens of different types of network framing
formats.
Gateway A gateway is a device which will interconnect two network
segments which utilize different communications
architectures. Gateways typically function on a programtype
by program-type (application) basis.The gateway maps
(or translates) data from one application to another
application and as such operates at level 7 (Application) of
the OSI Network Model.
Packet filter Packet filtering is a capability usually added to routers, but
can be implemented in host or firewall systems as well.
Packet filtering applies a set of filters (or rules of traversal)
to all packets entering or leaving the filtering mechanism
that enable the router to decide whether the packet should
be forwarded or disregarded. For instance, security
configurations may add address filters for certain ranges of
addresses to keep traffic from roaming all over a network or
to keep undesireable addresses from accessing resources
that are restricted in access.
Firewall A firewall is a description of a system (one or more pieces
of hardware) that acts as a barrier between two or more
network segments. A firewall can be used to provide a
barrier between an internal network and the Internet. A
firewall can be considered the technical implementation of a
security policy. The firewall upholds the security policy of a
network when connecting that network to a second network
which has a less stringent security policy.
Cyberwall A cyberwall is similar in scope to a firewall, but instead of
offering perimeter defense filtering between two or more
networks, cyberwalls are typically installed on desktop and
server systems on the inside network at a corporate site.
Cyberwalls provide a defensive barrier to attacks on
mission critical systems on internal networks and help
“harden” the operating system environment from a network
attack. Some cyberwalls also include intrusion detection
software to allow the system to detect an attack of specific
types in progress and effect some levels of defense against
them.
Readers are cautioned that these terms are not always used in a consistent manner
in publications which can cause confusion or misconceptions.
Routing
There are two types of routing used by the Internet: source routing and dynamic
routing. The Internet is a very robust networking system. The network routers will
automatically (dynamically) send out messages to other routers broadcasting routes
to known domains and addresses. If a network or router goes down, packets can be
dynamically rerouted to the destination. The user does not usually know how a
packet will be routed to the destination. The packet could be rerouted through an
untrusted network and intercepted. A router connected to the Internet should be
configured to ignore dynamic routing changes and the routing tables should remain
static. If the routing tables must be changed, then they should be changed by the
network administrator after understanding the reasons for the changes.
Unfortunately this is not usually convenient for Internet connected routers. This is
another example of when a tradeoff must be made. If the router is configured in this
manner then the dynamic routing that the Internet depends on would be disabled. In
this situation your network could be cut off (completely or partially) until the Network
Administrator makes the required changes in the routing tables.
The second type of routing is known as source routing. In this method of routing a
user is able to define a route for the packet between the source and destination. All
packets returning to the destination will follow the route information given. A hacker
can use a source routed packet to spoof another address. Computers and routers
connected to external networks should be configured to ignore source routed
packets.
Internet Applications and Protocols
The Internet is a global collection of networks all using the TCP/IP network protocol
suite to communicate. The TCP/IP protocols allow data packets to be transmitted,
and routed from a source computer to a destination computer. Above this set of
protocols reside the applications that allow users to generate data packets. The
following sections describe some of the more common applications as well as some
security vulnerabilities and concerns.
A R C H I E
Archie is a system for locating public files available via anonymous ftp (see ftp for
vulnerability information). A program is run by an Archie site to contact servers with
public files and the program builds a directory of all the files on the servers. Archie
can then be used to search the merged directories for a filename and will provide a
list of all the files that match and the servers on which the files reside. Public Archie
servers are available and can be accessed using telnet, e-mail or an Archie client.
Once the filename/server pair has been found using Archie, ftp can be used to get
the file from the server. Archie can be used to find security related information(e.g. if
one looks up firewall, Archie will give all the matches and locations for information
on firewalls). Archie is limited in that it can only match on filenames exactly (e.g. if
the file contains information on firewalls but the author named it burnbarrier, Archie
will not find it if the search was for firewalls).
Archie can be exploited to locate anonymous ftp sites that provide world writable
areas that can then be used to store and disseminate illegal versions of software. In
this case, a hacker uses the Internet tool to gain legitimate access to the database
and then misuse the information.
DNS — DOMAIN NAME SYSTEM
DNS is a hierarchical, distributed method or organizing the name space of the
Internet. It is used to map human readable host names into IP addresses and viceversa.
A host sends a User Datagram Protocol (UDP) query to a DNS server which
either provides the IP address or information about a smarter server than itself.
Different groups are given the responsibility for a subset or subsets of names. The
number of names in each group gets larger from left to right. For example:
cse.dnd.ca, each level of the system is called a domain, cse represents the domain
of the Communications Security Establishment which is smaller and within the dnd -
Department of National Defense domain. The dnd domain is within the ca - Canada
domain. The elements of the domain are separated by periods. Queries can also be
made using TCP (port 53) and are called zone transfers. Zone transfers are used by
backup servers to obtain a copy of their portion of the name space. Zone transfers
can also be used by hackers to obtain lists of targets. The Computer Emergency
Response Team (CERT) advises that access to this port be only permitted from
known secondary domain servers. This prevents intruders from gaining additional
information about the system connected to the local network.
E - M A I L — E L E C T R O N I C M A I L
Electronic mail is probably the most widely used application on the Internet.
Messages are transported using a specific message format and the simple mail
transport protocol (SMTP). This protocol offers no security features at all. E-mail
messages can be read by a hacker residing on the network between the source and
destination of the message. As well, SMTP e-mail messages can be forged or
modified very easily. The SMTP protocol offers no message integrity or sender
authentication mechanisms.
Some security and a higher level of trust can be provided to SMTP by applying
some cryptographic measures to the message. If message integrity or sender
authentication are required then the application of a digital signature is called for. A
digital signature allows a user to authenticate the e-mail message just as a written
signature authenticates a document in today's paper world. Message confidentiality
can be obtained by applying an encryption algorithm to the message prior to
sending it.
SMTP — SIMPLE MAIL TRANSPORT PROTOCOL
SMTP is an application level protocol used to distribute e-mail messages between
computers. This protocol is very simple and understands only simple text based
messages and commands. All messages transferred between computers are in
ASCII form and are unencrypted. The message is available to everyone in the path
that the message takes. There is no method of verifying the message source or
ensuring the message integrity, this must be done at a higher level using another
protocol such as PEM.
A common implementation of the SMTP protocol is found in the UNIX sendmail
facility. This program has a very colourful security history. Sendmail is an extensive
program which allows remote computers more access than required to drop off email.
SMTP is also commonly implemented in Post Office Protocol version 3 servers (also
known as POP3) and the new IMAP4 protocol used on newer e-mail servers on
Internet.
PEM — PRIVACY ENHANCED MAIL
PEM is a set of standards for adding a security overlay to Internet e-mail providing
message confidentiality and integrity. This set of standards describes a security
protocol that can be used above the common Simple Mail Transport Protocol
(SMTP) or the UNIX-to-UNIX Copy Protocol (UUCP). The PEM security
enhancements provide three security services: message integrity, message origin
authentication, and message confidentiality. The PEM enhancements can be used
as a foundation to provide non-repudiation for electronic commerce applications.
Currently the PEM standard defines the use of the RSA public key algorithm to be
used for key management and digital signature operations, and the DES algorithm
is included for message confidentiality encryption.
The PEM protocols rely on the trusted distribution of the public keys. PEM public
keys are distributed within an X.509 certificate. These certificates are digitally signed
by a certification authority. The PEM user trusts a certification authority to provide
public key certificates. The certification authorities can also cross certify public key
certificates from another certification authority. The certification authorities are
distributed in a hierarchical structure with the Internet Policy Registration Authority
(IPRA) at the top. The IPRA will certify the certification authorities. The IPRA is a
non-government, private agency and may or may not be trusted by an organization.
ENTRUST AND ENTRUST-LITE
Entrust is an cryptographic module that is being developed by Bell Northern
Research (BNR). This module will be available for multiple computer platforms and
operating systems. The module provides an Application Interface for user
applications to utilize the cryptographic functions. This module will provide the
cryptographic functionality required for both message and document integrity (Digital
Signatures) as well as message/document confidentiality.
This cryptographic module is being validated by the Communications Security
Establishment against the FIPS 140-1 standards.
PGP — PRETTY GOOD PRIVACY
PGP is a public key encryption package to protect e-mail and data files. It lets you
communicate securely with people you've never met, with no secure channels
needed for prior exchange of keys. It's well featured and fast, with sophisticated key
management, digital signatures, data compression, and good ergonomic design.
This program provides the RSA algorithm for key management and digital
signatures, and uses the IDEA algorithm to provide confidentiality. The program is
available for non-commercial use to Canadian citizens from the site
ftp://ftp.wimsey.bc.ca. There is commercial version of this program for sale from
ViaCrypt, and an international version available as well. The international version
has the message encryption (IDEA algorithm) functionality removed.
RIPEM — RIORDAN'S INTERNET PRIVACY-ENHANCED MAIL
RIPEM (pronounced RYE-pehm) is a public key encryption program oriented toward
use with electronic mail. It allows you to generate your own public keypairs, and to
encrypt and decrypt messages based on your key and the keys of your
correspondents. RIPEM is free, but each user is required to agree to a license
agreement which places some limitations on its use.
MIME — MULTIPURPOSE INTERNET MAIL EXTENSIONS
MIME is an Internet Engineering Task Force (IETF) solution that allows users to
attach non-text objects to Internet messages. A MIME-capable e-mail client can be
configured to automatically retrieve and execute data files that are attached to an email
message. The MIME standard provides a standard method of providing
attachments to e-mail messages. Some of the MIME e-mail programs allow the user
to configure what type of attachments are accepted and how they are interpreted,
other programs are not configurable. Users are cautioned to disable the automatic
execution and interpretation of mail attachments.
The attachments can be examined
and processed after the user responds to prompt. In this configuration the user is
warned that an attachment is going to be processed and the user has the option of
cancelling that processing if they are unsure of the consequences.
There is a system in development called atomicmail. Atomicmail is described as a
language for interactive and computational e-mail. This language is being developed
to provide portability between computer systems for the advanced e-mail
attachments as well as to address security concerns. The atomicmail language is
being designed with the constraints that processing does no harm and that access
to the operating system, CPU, files and other resources is tightly controlled.
File Systems
AFS — ANDREW FILE SYSTEM
AFS is a networked file system with similar functionality to NFS. This file system is
newer in design and can interoperate (to some degree) with NFS file systems.
Unlike NFS, the AFS designers placed security in the protocol and incorporated the
Kerberos authentication system into the file protocol.
NFS — NETWORK FILE SYSTEM
NFS is a Remote Procedure Call (RPC) based facility which utilizes port 2049. This
facility allows NFS-capable clients to mount a file system on a NFS server located
on the network. Once the NFS file system has been mounted it is treated like a local
file system. If an internal system exports a file system to external systems, then the
file system is available to a hacker across the network. Even if the file system is
exported to only a select set of clients the possibility of a hacker spoofing one of
those clients is possible. As well, it might be possible for a hacker to hijack an
existing NFS connection. NFS should never be allowed across a firewall to an
external network such as the Internet.
FTP — FILE TRANSFER PROTOCOL
FTP allows a user to transfer text or binary files between two networked computers
using ports 20 and 21. The ftp protocol uses a client-server structure with a client
program opening a session on a server. There are many "anonymous ftp servers"
located across the Internet. An anonymous server allows anyone to log on and
retrieve information without any user identification and authentication (the user gives
the username "anonymous" or "ftp").
If an anonymous ftp server allows world writable areas then the server could be
used to distribute malicious or illegal software. A server could also be the source of
computer viruses, trojan horses or other malicious software.
CERT provides a document on setting up an anonymous ftp server which is
available via anonymous ftp from:
ftp://info.cert.org/pub/tech_tips/anonymous_ftp
This document describes the procedures of configuring an anonymous server, with
restricted access. The procedures for restricting access to incoming files are also
provided. Even though access to incoming files is restricted, a hacker is able to
deposit corrupt, malicious, or illegal software on a server; it is unavailable however,
until the server administrator reviews the software and moves it to the archive of
retrievable software.
GOPHER
Gopher is a client-server system designed to locate and retrieve files or information
from servers, "gopher holes", across the Internet. When a user initiates a connection
to a Gopher server, the user is presented with a menu of data topics to choose from.
When a user selects a topic, Gopher returns access information and a data type
description. The access information tells the client program what IP address, port
and filename to access. The data type description informs the client program how to
interpret the raw information that is being retrieved. The data types include text and
graphic files, script programs and binary executable files. If software is retrieved and
executed automatically without user intervention then malicious code (e.g. viruses or
trojan horses) could be obtained and executed without prior screening. Therefore,
software should not be executed until it has been screened by a virus checker.
For those trivia hounds, it was originally developed at a U.S. university whose
mascot was a gopher…
ICMP — INTERNET CONTROL MESSAGE PROTOCOL
The ICMP protocol is used to determine routing information and host status. An
ICMP redirect packet is used to inform a router or computer about "new and
improved" routes to a destination. These packets can be forged providing false
routes to a destination to allow an attacker to spoof another system.
Another common ICMP packet is known as the ICMP unreachable message. These
packets indicate problems with a route to a destination address. A false ICMP
unreachable message could be used to deny access to another network or host. If
this type of vulnerability is of concern to your organization then the routing server or
firewall can be configured to ignore ICMP unreachable messages. The drawback of
this configuration is that if the packet is genuine and a host is actually unreachable,
the network routing tables will still not be updated and users will not know that the
host is not available. They will simply be denied access.
Ping is a common ICMP based service. Ping sends a packet to a given destination
which in effect says "Are you alive?" The destination returns an acknowledgement to
the ping or an ICMP unreachable message may be returned by a routing system in
the path. PING also has an ugly and sordid history in its use in network attacks and
in network infiltrations.
ICMP packets should be filtered and not allowed across network boundaries.
LPD — LINE PRINTER DAEMON
LPD allows networked computers to access printing services on another computer.
If lpd packets (destined for port 515) are allowed to be printed on an internal print
server from external sources, a hacker could deny printing services to internal users
by monopolizing the printer. This can be prevented by applying quotas, such as,
limiting amount of time the printer can be used, time of day it can be used, etc. This
can also be prevented by denying external network access to the printer.
NNTP — NETWORK NEWS TRANSFER PROTOCOL
NNTP is an application level protocol which is used to distribute news groups. This
protocol provides an unauthenticated and unsecured transfer service. The
information passed between computers using this protocol is not encrypted and can
be read by anyone with a network monitoring device located in the information
pathway. Since there is no authentication, neither the integrity nor the source of the
information can be guaranteed.
To provide some sort of information integrity or confidentiality, a higher level of
security protocol must be applied to the news messages. One example of this type
of security service is the PEM protocol.
NEWS READERS
Network news readers are applications which provide the user with access to NNTP.
The news readers usually do not require privileges to run and therefore can only get
access to the files owned by the user running the news reader. One concern with
these applications is that they do not control the flow of information. An organization
cannot control the content of the message; the news reader will not screen
information.
NIS — NETWORK INFORMATION SERVICES
NIS was originally developed and known as "yp or yellow pages". The NIS protocol
acts in a client server type of fashion where the server provides user and host
information to a client. The NIS system provides a central password and host file
system for networks of computers. It is possible for a hacker to inform an NIS client
to use another NIS server to authenticate logins. If this was successful then a
hacker could gain unauthorized access to the client computer.
A hacker can use the NIS protocol to gain information about the network
configuration including host and usernames. The more information that a hacker has
available, the easier it is to break into a system. NIS should never be allowed across
a firewall to an external network such as the Internet.
RPC — REMOTE PROCEDURE CALL
A RPC is similar to a procedure call in the C programming language. The difference
is that the procedure call includes a remote IP address and port. The procedure is
called from one computer and is executed on another computer across the network.
The network file system (NFS) works in this manner. These procedure calls and
ports can be used by a hacker to obtain unauthorized access to resources and
information on a system. RPC calls should be filtered and not allowed across
network boundaries.
The unfortunate thing about RPC’s is that programs, such as certain Windows 32 bit
applications, require RPCs to operate. Because so many ports must be opened to
support the RPC functionality, the additional application flexibility also causes major
and serious security problems.
R - U T I L S ( R L O G I N , R C P , R S H )
These utilities came with the original Berkly version of UNIX. These utilities allow a
"trusted" user from a known host to login or execute commands on another network
computer. No user identification and authentication is required, since these systems
assume a trusted user and host. If a hacker was to spoof one of the trusted hosts,
then unauthorized access could be possible. These utilities should never be allowed
across a firewall to the Internet.
SNMP — SIMPLE NETWORK MANAGEMENT PROTOCOL
The SNMP protocol allows a network administrator to manage network resources
from a remote node. This protocol should never be allowed through a firewall
connected to the Internet. A hacker would have the ability to remotely manage and
change the configuration of network systems. It would also allow a hacker to rewrite
the security policy of the internal network.
T E L N E T
Telnet is an application which allows a user to log in to a remote computer. Telnet
transmits all data between computers in an unencrypted fashion (including the
username and password pair). A hacker located on the routing path could monitor
all information transferred and pick up sensitive data or the username-password that
was used. As well, an ambitious hacker could possibly hijack an existing telnet
session. If a hacker gained access to a telnet session then all system resources
available to the authorized user would be compromised. A possible solution for this
is to use an encryption scheme with telnet.
Telnet is also used as the connection method for most network infrastructure
devices such as routers, bridges and lower-level hardware such as CSU/DSU
facilities on leased lines and frame relay connections. It has great potential to allow
a hacker access to a great deal of very sensitive hardware that can cripple a
network if compromised.
TFTP ? TRIVIAL FILE TRANSFER PROTOCOL
TFTP is mainly used for remotely booting another networked computer and
operates on port 69. A computer can initiate a tftp session to a boot server and
transfer the system boot information it requires to start up. This protocol should be
disabled if not required and should never be allowed across a firewall to the Internet.
TFTP can also be used to transfer and deposit information to a networked computer. An attacker could use this protocol to grab sensitive data, password files
or to deposit compromised system files. TFTP should not be allowed.
TFTP is also the most common protocol used to download bootstrap kernel software
for diskless systems such as routers. Compromise of TFTP host systems on a
network can cause a great deal of security problems for a customer network.
M O T I F
Motif is a graphical environment developed by the Open Software Foundation (OSF)
as a front end for the X11 X-windows interface. The vulnerabilities of the X-Windows
system are described below.
OPENWINDOWS
Openwindows is a graphical environment developed by Sun for its SunOS and
Solaris operating systems. This system is now publicly available within other
versions of the UNIX operating system. This graphical environment is similar to the
Xwindows system, however, it connects to port number 2000.
WINSOCK
Winsock is a Microsoft Windows dynamic link library providing TCP/IP port services
to windows applications. These services allow users to run many Internet tools,
such as Archie, Cello, ftp, Gopher, Mosaic and telnet on an MS-DOS/MS-Windows
computer.
WINDOWS — X11
X windows is a graphical environment for user application software. This
environment supports distributed services using TCP ports numbered 6000+. This
system is designed to remotely control and display processes across the network. It
is possible for a malicious process to monitor or take control of the screen, mouse
and keyboard devices. The opening of so many ports also allows the intruder an
opportunity to use an open port to compromise a trusted network from an untrusted
connection.
WAIS — WIDE AREA INFORMATION SERVERS
This is another of the WWW family of applications and protocols. (see http for
vulnerability information)
WWW — WORLD WIDE WEB
WWW is a new family of applications and protocols developed to provide users with
a convenient method of accessing information across the Internet. (see http for
vulnerability information)
HTTP — HYPERTEXT TRANSFER PROTOCOL
HTTP is the application level protocol used to access world wide web (WWW)
servers and information. Http is similar to the Gopher protocol; it transfers an
information block and a data type description to the client. The client program
(Internet Explorer, Mosaic, Lynx, and Netscape Navigator are common client
applications) is responsible for interpreting the information and presenting it to the
user in the correct form. As with the Gopher protocol, executable code is a valid
data type to be retrieved. Some client programs can be configured to automatically
interpret and process the information that is retrieved. If this protocol is supported
care should be taken to configure client programs to prompt prior to executing any
script or executable programs. Any executable code retrieved should be scanned for
viruses, trojan horses or other malicious activities before being executed.
A potential solution is s-http, which is intended to be a secure version of the http
protocol. The s-http protocol is still in development and further information will be
sent automatically if an e-mail message is sent to: info@commerce.net. This
protocol uses the PEM standard for mail and data exchange and provides the PEM
capabilities above the http protocol. In this manner all data
exchanged between an http server and client can be both authenticated and/or
encrypted as required.
Another standard in progress is the SSL or Secure Sockets Layer activity. This
standard provides a security layer between the TCP and application protocol layers.
SSL can be used to provide integrity (proof of sender) and confidentiality for any
TCP data stream. This security protocol can be used with all applications level
protocols not just http.
Direct Link - http://a.nnotate.com/php/pdfnotate.php?d=2009-01-24&c=OaL3alj9
Waseem Khan
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