Scanning, Sniffing, Spoofing andMan-in-the-middle Attacks

Scanning, Sniffing, Spoofing andMan-in-the-middle Attacks

Lesson 13

ScanningScanning

Ping Sweeps Port Scanners Application Scanning Operating System Scanning SNMP scanning Vulnerability Scanning

Ping SweepPing Sweep

PING (Packet INternet Groper)A utility designed to determine whether or not a remote system is accessible.

Using PING, attackers can send an ICMP echo request to every address within a range to determine which systems are “up and running”

Every system that is up will respond with an echo reply, providing a list of potential targets

PING SweepsPING Sweeps

Echo Request

Unused Address10.1.1.9

Attacker

Target List

Echo Request

Echo Request

Unused Address10.1.1.11

10.1.1.10

10.1.1.10

Echo Reply

PING SweepsPING Sweeps Less effective today than in the past

Recent rise in DoS attacks which also use ICMP have resulted in administrators setting their systems to drop inbound ICMP echo requests.

Can still be effective for insiders or attackers who have been able to penetrate at least one system.

There are a number of different packages that can be downloaded that accomplish this type of scan.

Port ScanningPort Scanning A Port Scanner is a program that checks a

computer’s TCP/IP stack for ports that are in the LISTEN state.

There are 65,535 possible ports– 1-1023 are considered “well known”– 1024-49151 are called “registered ports”– 49152-65,535 are dynamic or private ports

RFC 793 defines how TCP will react to FIN, ACK, and SYN packets.

RFC 793RFC 793If the state is CLOSED (that is, Transmission Control Block does not exist) then all data in the incoming segment is discarded. An incoming segment containing a RESET (RST) is discarded. An incoming segment not containing a RST causes a RST to be sent in response. The acknowledgment and sequence field values are selected to make the reset sequence acceptable to the TCP that sent the offending segment.

If the state is LISTEN then first check for an RST, An incoming RST should be ignored. Second check for an ACK. Any acknowledgment is bad if it arrives on a connection still in the LISTEN state. An acceptable reset segment should be formed for any arriving ACK-bearing segment. Third check for a SYN, if the SYN bit is set, check the security. IF the security/compartment on the incoming segment does not exactly match the security/compartment in the TCB then send a reset and return.

Some Well-known portsSome Well-known ports

Port Number Network Service 20 File Transfer Protocol (FTP) Data21 File Transfer Protocol (FTP) Control23 Telnet25 Simple Mail Transfer Protocol (SMTP)53 Domain Name Server (DNS)79 Finger80 World Wide Web (HTTP)110 Post Office Protocol – Version 3443 HTTPS

Port ScanningPort Scanning In a Port Scan, the system will attempt to connect to

specific (or all) ports on the remote system to see which respond.

Responding ports are considered “open” and the attacker can then attempt to exploit (especially known services on well-known ports).

Large number of tools available to perform port scanning. nmap is one of the most popular tools that can perform a port scan.

Port ScanningPort Scanning

Attacker

Web server

80

79

82

81

80

Services List

HTTP

Types of Port ScanningTypes of Port Scanning TCP SYN Scanning – “half open” scanning. Sends a SYN packet to each remote port.

Open ports respond with a SYN/ACK packet. Closed ports usually respond with an RST packet.

TCP FIN Scanning – Sends a FIN packet (normally sent to clear connection when conversation is finished). Closed ports usually respond with an RST packet. Open ports usually ignore FIN packets.

UDP Scanning – often more difficult than TCP since UDP services may not respond. If a ICMP “port unreachable” message is received, however, it is an indication the service is NOT running.

Fragmentation Scanning – break scan up into several smaller packets. This may result in being able to hide the scan from firewalls and IDS.

Relay or bounce scanning – send scan through another system (proxy or forwarding gateway), may confuse/hide origin of attack

Decoy scanning – send a large number of spoofed packets along with your real one so they hide the real scan.

nmapnmap

nmap ping sweepnmap ping sweep

nmap host scannmap host scan

Super ScanSuper Scan

Vulnerability ScanningVulnerability Scanning One approach to vulnerability scanning is to

Use a port-scanning tool such as nmap to identify the OS and to log all listening ports– May return something like

Linux Kernel 2.2 with ports 21, 25, 53, 80 listening– What the ports are and what vulnerabilities that may exist in them is an

exercise left up to the user. The purpose of a vulnerability scanner is to detect the

presence of specific vulnerabilitiesCommon components for vulnerability scanners– Vulnerability data – information about known vulnerabilities, how

knowledgeable is the tool?– Scanning mechanism – the “guts” of the scanner, how accurate is the tool?– Reporting mechanism – interface with user

Types of vulnerability scannersTypes of vulnerability scanners

Commercial scanners: developed and sold by companies (e.g. ISS and Cisco).Due to development time, often lag freeware scanners.

Freeware scanners: developed and released “in the community” General-purpose scanners: look for a wide range of vulnerabilities on a large number

of operating systems and applications. Often used in a security audit. Application scanners: written to examine a specific application for vulnerabilities

associated with it. Service scanners: Scanning tool used to examine a specific network service, such as

WWW, for common vulnerabilities associated with that service. Specific vulnerability scanners: written to only check for a specific vulnerability.

WhiskerWhisker

SNMPSNMP

Share SnifferShare Sniffer

Share SnifferShare Sniffer

Share SnifferShare Sniffer

Possible information from scanningPossible information from scanning Which systems are active What services are available/listening What operating system is in use Which version of an application is running Which users have an account on the system and which are active What the security configuration/settings are Whether certain patches have been installed Information about specific vulnerabilities Possibly whether a specific exploit will be successful

Ways to recognize scanningWays to recognize scanning

System log file analysis – look for multiple, short duration connections or connection attempts.

Network traffic – monitor the volume of inbound and outbound network traffic. If you have established a profile of what is normal activity you will be able to recognize spikes in the activity level which may indicate scanning activity.

Firewall and router logs – look for multiple rejections or access violations coming from the same source or group of sources.

Intrusion detection systems – most IDS contain built-in methods for examining traffic to detect scanning attempts.

Defending against Scanning and its effectsDefending against Scanning and its effects Block ports at your router/firewall. Block ICMP, including echo Create a DMZ Use bastion hosts/proxy servers Use NAT to hide private, internal IP addresses Remove default/sample materials Remove unnecessary services Restrict permissions Change default headers associated with services Keep applications and operating systems patched Establish a “Honeypot” to trap attackers

Scanning Your Own NetworkScanning Your Own Network

Will provide you with “hackers view” into your network

Will illustrate the most visible vulnerabilities Scan from both “internal” and “external” vantage

points

New Target – Wireless EthernetNew Target – Wireless Ethernet

802.11b WEP (Wired Equivalent Privacy)

40-bit encryption key and 24-bit Initialization Vector (64-bit encryption) 104-bit key plus the 24-bit Initialization Vector (128-bit encryption)

Most Access Points are deployed with no encryption, or with default keys

SniffingSniffing Sniffers are programs or HW devices that monitor

(“listen in to”) traffic flowing across a network.They can pull in all packets or be selective and only grab packets destined for certain addresses or that carry a certain type of traffic

For a sniffer to work correctly, it needs to view all of the traffic going across a network. Thus, it must be on an internal network or on a main connection into/out of a network.

Computer Network MonitoringComputer Network Monitoring

Port Scanning Keystroke Monitoring Packet sniffers

takes advantage of “friendly” nature of net.Grabs packets not destined for systemused by– hackers– sysadmins– Law enforcement agencies

IP PacketIP Packet

Version Length Type of Srvc Total Length

Identification Flags Fragment Offset

Time to live Protocol Header Checksum

Source Address

Destination Address

Options

Data

4 8 16 19 32

SnifferProSnifferPro

SnifferProSnifferPro

SnifferProSnifferPro

SnifferProSnifferPro

NetXrayNetXray

TCP packetTCP packet

Dataoffset

Unused

U A P R S FR C S S Y IG K H T NN

Window

Source Port

Urgent Pointer

Sequence Number

Acknowledgement Number

Options Padding

Data

4 8 16 32

Destination Port

Checksum

NetXrayNetXray

Van Eck receptionVan Eck reception

Relies on the fact that electronic equipment radiates electromagnetic signals which can be intercepted

With the proper equipment signals can be recreated up to 1 kilometer away

Seizing the SignalsSeizing the Signals

Eavesdropping on conversations“listening in”, the content

Traffic analysisdata about the signals themselves

EavesdroppingEavesdropping

Cellular Interceptsextremely vulnerable to interception

Pager Interceptsalso fairly simple

Law Enforcement Wiretapsgenerally require court order with probable cause

Foreign Intelligence InterceptsUS and others have VERY active program in this arena

Defeating Sniffer AttacksDefeating Sniffer Attacks Detecting and Eliminating Sniffers

Possible on a single box if you have control of the systemDifficult (depending on OS) to impossible (if somebody splices network and adds hardware) from network perspective

Safer TopologiesSniffers capture data from network segment they are attached to, so – create segments

EncryptionIf you sniff encrypted packets, who cares?– (outside of traffic analysis, of course)

Traffic AnalysisTraffic Analysis Looks at activity, not contents Pen Registers and Trap & Trace

pen registers provide access to the numbers that are dialed from a phonetrap & trace provides incoming numbers

Location Trackingpossible with cellular phonescan work even when phone not in use

SpoofingSpoofing

“a sophisticated technique of authenticating one machine to another by forging packets from a trusted source address.”

IP SpoofingIP Spoofing

This may simply consist of forging the from address in an IP packet so it appears to have come from somewhere else.

Often used to trick target machine into believing packet is coming from a host it trusts, thus getting the target machine to perform some task.

To do appropriately it may involve sniffing, spoofing, and DoS attack

Two themes present in these definitionsTwo themes present in these definitions

Trust“the relationship between machines that are authorized to connect to one another.”

Authentication“the process those machines use to identify each other.”

Generally these two have an inverse relationship:If a high degree of trust exists between two machines, the amount of authentication is low.If little trusts exists between the machines, a great deal of authentication is required.

Authentication and TrustAuthentication and Trust Most common method of authentication is the

userid/password combination. If a user on a local network wants to access another

system on the local network, having to supply the password to log on is a nuisance. Consequently, a trusted relationship may be established where one local system will trust the other to have authenticated the user originally and will thus not require additional authentication.

An example of this is the UNIX .rhosts and hosts.equiv files.

Trusted relationships in UNIXTrusted relationships in UNIX

.rhosts file is used to establish a trusted relationship between machines. Used by rlogin, rsh, and rcp to determine which remote hosts and users are considered “trusted” and are allowed to access the host without supplying a password.

rlogin (remote login), rsh (remote shell), rcp (remote copy) File consists of

A host name, indicating that this user is trusted when accessing the system from the specified host, orA host name followed by a login name, which indicates that the listed login name is trusted when accessing the system from the specified host

.rhosts example.rhosts example If user1 had the following .rhosts file in their home directory

(/home/user1/.rhosts)system2system4system5 user2system2 user5

It would mean user1 could log in from system2 as user1 user1 could log in from system4 as user1 user1 could log in from system5 as user2 user1 could also log in from system2 as user5

/etc/hosts.equiv file example/etc/hosts.equiv file example /etc/hosts.equiv are essentially equivalent to a system-

wide .rhosts file and contain lines with hostnames. If system1 contained the /etc/hosts.equiv file:

system2system4system5

It would indicate that any user on system2, system4, or system5 could log into system1 without having to supply a password.

This assumes that an equivalent username exists on system1 as the one being used on the accessing system (i.e. system2, system4, or system5).

A + in the /etc/hosts.equiv file says all systems trusted.

Authentication and UNIX Trusted relationshipsAuthentication and UNIX Trusted relationships

UNIX will base its trust decision, using the .rhosts or hosts.equiv files, on the IP address of the connecting system.

But…. The IP address (and most other fields) of an IP header can be forged!!!

IP Spoofing on LANIP Spoofing on LAN

Attacker

Trusted System 1 Trusted System 2

Attacker

This is System 1,Please send file A

OK, here it is...

Huh? I didn’t ask for that...

IP Spoofing on LAN

Attacker

Trusted System 1 Trusted System 2

Attacker

This is System 1,Please send file A

OK, here it is...

DoS attacklaunched

Attacker usessniffer to grabfile

IP Spoofing across the Internet

Attacker

Trusted System 1 Trusted System 2

Attacker

This is System 1,Please add user Xto your password file

OK, I’ve done it

DoS attacklaunched

Login asuser X

SpoofingSpoofing

In the preceding slides, the actions represented by the “OK, I’ve done it” or the “OK, here it is” lines may actually consist of a series of messages with appropriate responses.

The attacker knows what the responses should be, so the attacker can send them, timed appropriately, to ensure the connection is maintained.

Blind spoofingBlind spoofing

In non-blind spoofing the response sent by the target machine can be observed (sniffed).

In blind spoofing, the target’s responses can not be observed.

The steps of a spoofing attackThe steps of a spoofing attack Identify the target of the attack (a system with a trusted

relationship with another). “Eliminate” (DOS attack) the host you wish to spoof. Forge the address of the host being spoofed in your

packet to be sent to the target. Send the spoofed packet to the target Keep the connection active by guessing the correct

sequence number used by the target machine.

Sequence numbersSequence numbers

Used to acknowledge receipt of data. Remember 3-way handshake process

Client sends TCP packet with an initial sequence number.Server responds with it’s own sequence number and an acknowledgement (ACK).The client acknowledges receipt by sending packet with server’s number plus one.

Guessing the sequence numberGuessing the sequence number

For non-blind spoofing, no problem as you can see the responses.

For blind spoofing:Contact the target and attempt several connectionsTarget will respond with a sequence number for eachAnalyze the responses to determine the pattern the target uses for incrementing

Once you’ve succeeded…Once you’ve succeeded…

Attempt to secure a better connectionModify password fileModify hosts.equiv or .rhosts file

Shut down spoofed connection (stop the DOS attack). Now log into the target host using new account or based on trusted relationship.

Spoofing Prevention TipsSpoofing Prevention Tips

General rule of thumb: Don’t have any trusted relationships if you can help it.

Don’t accept packets from outside of your network that claim to be originating from inside of your network.

Man-in-the-Middle AttacksMan-in-the-Middle Attacks

Name given to a type of spoofing attack where the intruder assumes a position between the two legitimate users and

Simply listens in (thus really just sniffing)Relays information, thus can substitute appropriate public key to convince the legitimate users that their communication is secret, when it isn’t.

Man-in-the-middle attackMan-in-the-middle attack

Public KeyRepository

SystemA

SystemB

What is System B’sPublic Key?

Here it is

Message sent usingSystem B’s public key

Man-in-the-middle attack

Public KeyRepository

SystemA

SystemB

What is System B’sPublic Key?

Here it is

What is System A’sPublic Key?What is System B’sPublic Key?Here it isHere it is

Quick DoSOn System AMessage sent using New

System B’s public key

Hi, I’m System B,Here is my new Public key

Quick DoSOn System BMessage sent using New

System A’s public keyMessage sent using

System B’s public keyMessage sent using

System A’s public key

Hi, I’m System A,Here is my new Public key

What is System A’sPublic Key?

Here it is

SummarySummary

What is the Importance and Significance of this material?

How does this topic fit into the subject of “Voice and Data Security”?