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German Research Center forArtificial Intelligence

Network SecurityNetwork Security


Malware - SummaryMalware - Summary

• Virus:– program which is included in other

programs and can reproduce itself• Worm:

– program that distributes itself via the network

• Trojan horse:– program that hides additional

functionality useful for an adversary• Rootkit:

– faked OS providing additional functionality (for an attacker) but simulating original OS (almost) perfectly: e.g. faked versions of ls, ps, nstat, etc.


Vulnerabilities all over the timeVulnerabilities all over the time

• see http://nvd.nist.govRecent CVE VulnerabilitiesCVE-2006-3349 Publish Date: 7/3/2006 Multiple SQL injection vulnerabilities in SmS Script allow remote attackers to execute arbitrary SQL commands via the CatID parameter in (1) cat.php and (2) add.php. CVE-2006-3348 Publish Date: 7/3/2006 Multiple SQL injection vulnerabilities in HSPcomplete 3.2.2 and 3.3 Beta and earlier allow remote attackers to execute arbitrary SQL commands via the (1) type parameter in report.php and (2) level parameter in custom_buttons.php. CVE-2006-3347 Publish Date: 7/3/2006 SQL injection vulnerability in index.php in deV!Lz Clanportal DZCP 1.3.4 allows remote attackers to execute arbitrary SQL commands via the id parameter. CVE-2006-3346 Publish Date: 7/3/2006 SQL injection vulnerability in tree.php in MyNewsGroups 0.6 allows remote attackers to execute arbitrary SQL commands via the grp_id parameter. CVE-2006-3345 Publish Date: 7/3/2006 Cross-site scripting (XSS) vulnerability in AliPAGER, possibly 1.5 and earlier, allows remote attackers to inject arbitrary web script or HTML via a chat line. CVE-2006-3344 Publish Date: 7/3/2006 Siemens Speedstream Wireless Router 2624 allows local users to bypass authentication and access protected files by using the UPnP (Universal Plug and Play)/1.0 component. CVE-2006-3343 Publish Date: 7/3/2006 PHP remote file inclusion vulnerability in recipe/cookbook.php in CrisoftRicette 1.0pre15b allows remote attackers to execute arbitrary PHP code via a URL in the crisoftricette^parameter. CVE-2006-3342 Publish Date: 7/3/2006 Cross-site scripting (XSS) vulnerability in index.php in Arctic 1.0.2 and earlier allows remote attackers to inject arbitrary web script or HTML via the query parameter in a search cmd. CVE-2006-3341 Publish Date: 7/3/2006 SQL injection vulnerability in annonces-p-f.php in MyAds module 2.04jp for Xoops allows remote attackers to execute arbitrary SQL commands via the lid parameter. CVE-2006-3340 Publish Date: 7/3/2006 Multiple PHP remote file inclusion vulnerabilities in Pearl For Mambo module 1.6 for Mambo, when register_globals is enabled, allow remote attackers to execute arbitrary PHP code via the (1) phpbb_root_path parameter in (a) includes/functions_cms.php and the (2) GlobalSettings[templatesDirectory] parameter in multiple files in the "includes" directory including (b) adminSensored.php, (c) adminBoards.php, (d) adminAttachments.php, (e) adminAvatars.php, (f) adminBackupdatabase.php, (g) adminBanned.php, (h) adminForums.php, (i) adminPolls.php, (j) adminSmileys.php, (k) poll.php, and (l) move.php. CVE-2006-3339 Publish Date: 7/3/2006 secure/ConfigureReleaseNote.jspa in Atlassian JIRA 3.6.2-#156 allows remote attackers to obtain sensitive information via unspecified manipulations of the projectId parameter, which displays the installation path and other system information in an error message. CVE-2006-3338 Publish Date: 7/3/2006 Cross-site scripting (XSS) vulnerability in Atlassian JIRA 3.6.2-#156 allows remote attackers to inject arbitrary web script or HTML via unspecified vectors in a direct request to secure/ConfigureReleaseNote.jspa, which are not sanitized before being returned in an error page. CVE-2006-3337 (cPanel)Publish Date: 7/3/2006 CVSS Severity: 4.7 (Medium) Cross-site scripting (XSS) vulnerability in frontend/x/files/select.html in cPanel 10.8.2-CURRENT 118 and earlier allows remote attackers to inject arbitrary web script or HTML via the file parameter.

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A Closer Look – CVE-2006-3344A Closer Look – CVE-2006-3344

• Digital Armaments advisory is 05.02.2006

• http://www.digitalarmaments.com/2006290674551938.html

• I. Background

• The SpeedStream Wireless DSL/Cable Router is usually adopted for home and small business solutions. Together with an existing DSL or cable modem connection, this affordable, easy to use connection sharing solution brings the freedom of high-speed, wireless broadband connectivity to home and SOHO networks. Its comprehensive functionality provides vital firewall protection, IP sharing capabilities, and fundamental routing features that support popular protocols like NetMeeting and VPN.

• For further information or detail about the software you can refer to the vendor's homepage:

• http://subscriber.communications.siemens.com/

• II. Problem Description

• Speedstream routers have UPnP/1.0 support. An attacker can access protected files and bypass the password protection without login using the UPnP part of the tree.

• III. Detection

• This problem has been detected on latest version of Siemens Speedstrem Router. It has been tested on the Speedstream 2624.

• IV. Impact analysis

• Successful exploitation allow an attacker to bypass the password protection. It also allow an attacker to access protected files without login.

• V. Solution

• First notification 05.02.2006.

• Second notification 05.20.2006.

• No answer from the vendor.

• VI. Credit

• Jaime Blasco - jaime.blasco (at) eazel (dot) es [email concealed] is credited with this discovery.


InternetInternet

• Internet as „the“ network• Based on the early 70th ARPA-network

(Advanced Research Projects Agency)

• Internet protocols– IP: internet protocol– ICMP: internet control message

protocol– TCP: transmission control protocol– ARP: address resolution protocols


TCP/IP - Model (a la ISO/OSI)TCP/IP - Model (a la ISO/OSI)

FTP, SMTP, HTTP

TCP, UDP

IP

Application-layer

Transport-layer

Network-layer

Data link-layer

Physical-layer

FTP, SMTP, HTTP

TCP, UDP

IP

bitstreams

frames

Packages, routing

Reliable protocol


IP – SecurityIP – SecurityPrivacyPrivacy

By 2010, driven by the improving capabilities of data analysis, privacy will become a meaningless concept in Western societies

Gartner group

If privacy is outlawed, only outlaws will have privacy

Phil Zimmermann


PhishingPhishing

• Social engineering (bank customers)• Faking web pages of bank

– mismatch of real and visible URLs• Requesting PIN/TAN from customers


Network Services - DNSNetwork Services - DNS

• Domain Network Service provides translation of host names (www.uni-sb.de) to IP-addresses (e.g.134.96.7.73)

• DNS-server provide two data bases:– IP-addresses -> host names (reverse lookup)– Host names -> IP-addresses (lookup)

• No mechanisms to secure consistency of tables!

• DNS-server are distributed


Pharmining - DNS-SpoofingPharmining - DNS-Spoofing

• Faking of the reverse -lookup table– Reverse lookup (e.g. for rlogin) provides Bobs host

name instead of Eve‘s for Eve‘s IP-address– Access to Alice‘s host if Bob is member of

/etc/hosts.equiv or in .rhosts– Countermeasure: forward and reverse lookup

• Sending faked update messages to the cache of DNS-server

• Manipulating C:\windows\system32\drivers\etc\hosts


Observations of Users in NetworksObservations of Users in Networks

X

eavesdropper

Switch

staff

XSwitch

staff

Link-to-link encryption:


Observation of Users in Observation of Users in Switched NetworksSwitched Networks

XSwitch

staff

Link-to-link encryptionEnd-to-end encryption of content

Problem of traffic data: who communicates with whom, how long, where?


Abilities of a Potential AttackerAbilities of a Potential Attacker

Worst case analysis:• Observation of all communication channels• Generation of new messages• Operating some network services (e.g. as an

anonymity service, as a web server, etc)

• No break of cryptographical systems• No attack on user‘s personal machine• Limited time and computing power


Anonymity and UnobservabilityAnonymity and Unobservability

Anonymity:• Sender and/or receiver stay anonymous to each

other

Unobservability:• All parties cannot trace communication relations• Sending and receiving of messages is

unobservable

Pseudonym:• identity can only be revealed in special cases


Anonymity and UnobservabilityAnonymity and Unobservability

Need for a group of users where all users behave similarily

Events

Anonymity group

Everybody can be the originator of an event with equal possibility


Simple ProxiesSimple Proxies

• Proxy gets an URL on behalf of the user• Server has no information about the real originator of

the request

• Examples: – Anonymizer.com (Lance Cottrel)– Aixs.net– ProxyMate.com (Lucent, Bell Labs)

User ServerProxy


Problems with Simple ProxiesProblems with Simple Proxies

• No protection against the operator • No protection against traffic analysis

– Timing correlation of incoming and outgoing requests

– Correlation by message length and coding

User 1

User 2

User n

...

httpproxy

GET page.html

GET page.html


Possible AttacksPossible Attacks

• Timing attacks:– Observe duration by linking possible endpoints of

communication, wait for a correlation between events at endpoints

• Message volume attacks:– Observe the amount of transmitted data

• Flooding attacks:– Almost all messages except the message to be

observed are created by the attacker• Linking attacks:

– Observe intersections of anonymity groups due to on/off-line periods (profiles)


BroadcastBroadcast

Message is sent to all participants

But only one person is able to read it


Mixes (David Chaum, 1981)Mixes (David Chaum, 1981)

• Collect messages in batches, change their coding and forward them at the same time but in different order

• Use of various mixes• If one mix is not corrupt then perfect

unlinkability of sender and receiver


Internals of MixesInternals of Mixes

Discard message repeats

Store incoming messages

Changecoding

Reordermessages

Wait for aSufficientNumber

Mix

Avoid replay attacks


Encryption of MessagesEncryption of Messages

• ci encryption with public key of Mixi

• Ai address of Mixi

• M message to be sent• ri : random numbers (to ensure indeterminism)

A1, c1(A2, c2(M, r2), r1)

A2, c2(M, r2),

M


Real Time AspectsReal Time Aspects

• Mixes are good for non-real time communication: E-mail

• Problems with real-time applications like net-phone, ftp, www– Sampling messages yields high delay– Message length vary in a very large interval

or no support of connection oriented services


Traffic padding and Time SlicesTraffic padding and Time Slices

Waiting time

Traffic padding

Sending of random data to cover last message

Waiting time

Traffic padding


Dummy TrafficDummy Traffic

• Users (not Mixes) send messages all the time• Nobody can distinguish between encrypted

messages and faked ones (random numbers)• Increases amount of traffic if necessary• Avoiding high delay of messages


Flooding and AttacksFlooding and Attacks

• Flooding Attacks:– Introduction of tickets to be processed by a

Mix– Only one message of a user in one branch– Attacker needs help of other users

• Long-time observation:– Intersection of anonymity groups– No good solution known for this attack


IP – SecurityIP – SecurityAvailability, IntegrityAvailability, Integrity


Internet Control Message ProtocolInternet Control Message Protocol

• Transfer of error- and status- messages– destination unreachable: unreachable port (host)

• Forged message may cause abortion of all traffic to this hosts

– fragmentation needed• Continuing generation of faked message causes denial of

service

– Redirect : to change routing behaviour• Rerouting of all packets of a host via a malicous host

– Source quench : to reduce traffic caused by a host• faked message causes denial of service


Address Resolution Protocols (ARP)Address Resolution Protocols (ARP)

• Translating IP-names (e.g. 134.96.88.122) to real physical addresses (eg. 00:A0:C9:44.BA.20) inbuilt in the firmware of physical device

• ARP address-table of the router– Updated via broadcast messages („Who is?“)

• Masquerading: faked answers to broadcast messages• Denial-of-service: request for non-existing host is

broadcasted through gateways. Malicious host may even redistribute requests coming back!


TCP - ConnectionsTCP - Connections

• Logical connections between ports

• TCP-packet contains:– 32bit-addresses of sender and receiver– 32bit sequence number

• Randomly generated

• 3-phased handshake:

– Client -> Server: Seqc

– Server -> Client: SeqS, Ack = Seqc + 1

– Client -> Server: Ack = SeqS + 1

– Client -> Server: Data


Security in TCP - Sequence numbersSecurity in TCP - Sequence numbers

• Masquerading using sequence number attacks:

– To incorporate a malicious packet into an ongoing communication the intruder has to know the sequent number

– Implementations use 32bit counter to generate sequence number (instead random numbers)(counter is incremented every second by 1, new connections will increment counter by 64)

– Sequence numbers can be guessed


Security in TCP - Sequence numbersSecurity in TCP - Sequence numbers

• Eve -> Alice: Port 25, SeqEve

• Alice -> Eve: Ack: SeqEve + 1, SeqAlice

Guessing seqAlice‘ :

• Eve as Bob -> Alice: Port 513, SeqEve‘

• Alice -> Bob: Ack: SeqEve‘ + 1, SeqAlice‘

• Eve as Bob -> Alice: Ack: SeqAlice‘ + 1

Problem: answers of Bob are sent to Alice:Additional attack neccessary to flood Alice with requests to prevent Alice from sending reset- packets


Security Problems in IP: Denial of ServiceSecurity Problems in IP: Denial of Service

Address spoofing – Examples of denial of service:

– UDP-flood attack:• Eve sends UDP-packet with faked return-address• Target machine sends echo-packets to machine

of return address which echos etc...

– SYN-flood attack:• Eve sends SYN-packets with faked return

addresses of non-available machines• Target sends SYN-Ack packets• Overflow of SYN-stack


Distributed Denial of ServiceDistributed Denial of Service

Attack Attack

Attack

Attacker

Agent

Handler

Stepping stones


Intrusion Detection SystemsIntrusion Detection Systems

Intrusion Detection is the process of identifying and responding to malicious activity targeted at computing and network resources

Edward Amoroso


Intrusion Detection SystemsIntrusion Detection Systems

• Monitoring:– Examine and process information about

activities on the target system• Reporting:

– Report information about monitored system into a system security infrastructure

• Responding:– Respond to detected intrusion


Dimensions of IDSDimensions of IDS

• Analysis approach:– Attack signature detection identifies

patterns corresponding to known attack– Types of attacks have to be known in

advance

• Anomaly detection:– Identifies unacceptable deviation form

expected behaviour using profiles– Can respond to previously unknown types of

attacks


Methods of IDS Methods of IDS

• Audit trail processing:– Existing log-files are examined by IDS – Off-line– Auditable events, auditable information, audit basis– Example: Unix Syslog Audit Processing

• On-the-fly processing („network intrusion detection“)– Monitoring of traffic in real-time– Suspicious string patterns „/etc/passwd“– Signatures of abnormal behaviours – Warnings before damage can occur


Methods of IDS (II)Methods of IDS (II)

Anomality Detection

• Profiles of normal behaviourCapturing expectations about user and

system computing and networking activities– Estimation of initial profile– Fine-tuning of profiles– Profiling using all-source information


Architecture of an IDSArchitecture of an IDS

• Sensor: Provides necessary information about target• System management: maintain control over internal

components, communication with over IDS• Processing engine: reduction of irrelevant data, identification

of key intrusion evidence, decision-making of type of response• Knowledge base: profiles of user and data, attack signatures• Audit archive: storage of target system activities• Alarms• GUI


Intrusion ResponseIntrusion Response

• Identification of the attacker– DNS ???– Identification of intermediate hosts

• Preventing damages– Closing ports and network connections– Counter attack by denial of service attack ???

• Repair of existing damages– Loss of integrity, accessability,

authentication, privacy?


FirewallsFirewalls

• All traffic between intranet and open network is controlled by the firewall

• Security strategy, access control, protocols, authentication

Firewall Open network(Internet)

Intranet

e.g. router


Types of Firewalls Types of Firewalls

• Packet filter– Controlling IP (TCP) packets

• Circuit-level gateway– Operates on transport layer

• Application-level gateway (proxy server)– Operates on application layer– Can analyse application data


Packet FiltersPacket Filters

• Filters packets (TCP / IP) according to a security policy based on header information

• No internal state• Accessable information:

– Sender/receiver addresses, ports, options, ack-bit, type of protocol, ...

sender receiv. port proto. action reason* * 53 UDP ok DNS-queriesExtern intern 123 UDP ok NTP-access* * 69 UDP no no TFTPExtern * 513 TCP no no rlogin from outside

Rules:


Packet Filters - Pros and ConsPacket Filters - Pros and Cons

• Easy and cheap to implement• Transparent for upper layers• Prevents some IP-spoofing and router attacks

But:• Uses possibly faked IP-addresses and ports• No detailed filtering (e.g. according to users)• Error-pruned specification of filter table

– Large, unreadable tables– Need for tools


Circuit-level GatewayCircuit-level Gateway

• Controls the transport layer• Operates as client for the server and as server

for the client (proxy - server)• Provides generic proxy services• Has internal state and protocols activities• Example: SOCKS - gateway (Hummingbird)

– Provides socket access via rconnect, rlisten and rbind through gateway with authentication


Circuit-Layer Gateway - Circuit-Layer Gateway - Pros and Cons Pros and Cons

• Independent of applications• Allows for filtering of existing connections• Authorization and logging• Filtering of UDP services possible

But:• Do not consider application specific information

– Cannot distinguish http-content• Modification of application necessary


Application FilterApplication Filter

• Operating on application layer• Proxies for telnet, ftp, smtp, http, ...• Provides application specific knowledge

– E.g. ftp-proxy knows about ftp-commands– http-proxy about activeX, Javascript, JAVA...

• Internal state and logging


Application Filter - Pros and ConsApplication Filter - Pros and Cons

• Allows for sophisticated authentication and controlling (e.g. generating profiles)

• Accounting and logging of accesses– Intrusion Detection Systems

• Fine granular rules possible

But:• Individual fiter for each service - Automation ?• Based on unreliable lower layers


Architecture of FirewallsArchitecture of Firewalls

Intranet

Packet filter

Application filter

Dual-Home Firewall

Dua

l-Hom

e B

astio

n

InternetPacket filter

Intranet

NTP-server

Application filter

Internet

Screened-Host Firewall


Architecture of Firewalls (II)Architecture of Firewalls (II)

Internalhost

Application filterInternetPacket filter

Screened-Subnet Firewall

Internalwww-server

InternalDNS-server DNS

server

WWWserver

Packet filter


Firewalls - SummaryFirewalls - Summary

• Security mechanisms concentrated at one point• Fine-granular policies can be implemented• Logging features to create profiles

But:• Difficult to come up with consistent configuration• Continuous maintenance necessary• Problems with tunneling• Mobile devices: Laptops, Palms etc


IP – SecurityIP – SecurityAuthenticationAuthentication


Security Problems in IP - AuthenticationSecurity Problems in IP - Authentication

• Address - Spoofing:

– Faking the sender address in IP-packets

Alice.uni-sb.de(134.96.12.102)

Eve.evil.org(188.88.88.88)

Bob.uni-sb.de(134.96.12.104)

/etc/hosts.equiv :

Bob.uni-sb.de

From: 134.96.12.104To: 134.96.12.102

IP


Secure Socket Layer (SSL)Secure Socket Layer (SSL)

• SSL operates on top of the transportation layer• Developed by Netscape according the

recommendations of the OSI - security architecture • Authentication of communication partners

– Assymmetric encryption• Private communication

– Symmetric session keys• Integrity of messages

– Message Authentication Codes (MAC)• Encryption- and hashing algorithms are negotiated

between communication partners


SSL - OverviewSSL - Overview

TCP IP

SSL-Record

SSL-Handshake

Telnet, Ftp, http, Smtp,

TCP IP

SSL-Record

SSL-Handshake

Telnet, Ftp, http, Smtp,

Fragmentation of data,Compression,Computation of MACsand session-keys,Encryption of records

Authentication of partnersExchange of secrets


SSL - Handshake ProtocolSSL - Handshake Protocol

• Agree in SSL-communication by using specific ports:443 (https), 456 (ssmtp), 990 (ftps), 992 (telnets)

Client Hallo

ServerHelloCertificate (optional)ServerKeyExchange (optional)Certificate Request (optional)ServerHelloDone

Certificate (optional)Client Key ExchangeCertificate Validate (optional)ChangeCipherSpecFinished

ChangeCipherSpecFinished

Use Data


SSL - Handshake ProtocolSSL - Handshake Protocol

• ClientHello: timestamp (32bit), Nonce RC (28bit), SessionID, list of prefered encryption algorithms

• ServerHello: timestamp(32bit), Nonce RS, list of prefered encryption algorithms of client

• Certificates according X.509• ServerKeyExchange: temporary public key PKS (RSA) • ClientKeyExchange: 48bit secret „pre“ encrypted with PKS

(or public key of client in case of DiffieHellman)• Computing the master secret

MD5(pre, SHA(„A“ . pre . RC . RS)) | MD5(pre, SHA(„BB“ . pre . RC . RS)) | MD5(pre, SHA(„CCC“ . pre . RC . RS)) to compute secret keys

• Finished messages incorporate MAC/SHA of all previous message parts


Security of SSLSecurity of SSL

• SSL allows for an authenticated and private communication without manipulations

• Finished messages prevent man-in-the-middle attack

• Depends on used cryptographical algorithms (MD5? HMAC!)

• No use with application filter • TLS (transport level security) as „internet

standard“ based on SSL 3.1


IPSecIPSec

„Suite“ of protocols to secure network connections

• Allows for different encryption and authentication methods

• Integrity (authentication) and secrecy (encryption)

• Operates on the IP – level• IKE : Internet Key Exchange


IPSec - AlternativesIPSec - Alternatives

• AH („Authentication Header“): authentication vs.ESP (Encapsulating Security Payload): encryption + authentication

• Tunnel mode (total IP-packet) vs. transport mode (payload only)

• Different cryptographical choicesMD5, SHA-1…3DES, AES, Blowfish, …

• IKE (Internet Key Exchange) protocol vs. manual setup


Authentication Header – Transport ModeAuthentication Header – Transport Mode

Version Hdr.len TOSVersionIdentification

Length (max. 64k)Flags Fragment-Offset

TCPTime to Live Header checksum

Padding

Address of receiverAddress of sender

IP-options

DATA



IHTime to Live Header checksum

Padding


IP-options

DATA

Version AH-lenTCP ReservedSecurity Parameter Index

Sequence NumberAuthentication Data

Original IP-packet

IPSec-packet

Protected by Authentication Data

Changed entries


Authentication Header – Tunnel ModeAuthentication Header – Tunnel Mode




Padding


IP-options

DATA

Version AH-lenIP ReservedSecurity Parameter Index

Sequence NumberAuthentication Data

IPSec-packet

Protected by Authentication Data



AHTime to Live Header checksum

Padding


IP-options


ESP – Transport ModeESP – Transport Mode




Padding


IP-options

DATA



ESPTime to Live Header checksum

Padding


IP-options

Data

Security Parameter IndexSequence Number

Authentication Data

Original IP-packet

IPSec-packet

Encrypted Data

Changed entries

TCPpad-len


ESP – Tunnel Mode: VPNESP – Tunnel Mode: VPN




Padding


IP-options

DATA + Padding

Security Parameter IndexSequence Number

Authentication Data

IPSec-packet

Encrypted data



ESPTime to Live Header checksum

Padding


IP-options

Authenticated data

Changed entries

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